Article

Growth, feed utilization and growth heterogeneity in juvenile turbot Scophthalmus maximus (Rafinesque) under different photoperiod regimes

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Abstract

Juvenile turbot (45 g, SE = 1.3) were reared under three photoperiods, 08L:16D, 12L:12D and 20L:04D at slightly elevated ambient temperature for Ireland. Over the 297-day experimental period, the overall growth rate of the 12L:12D (0.82% d−1) treatment was higher than for both 08L:16D (0.80% d−1) and 20L:04D (0.77% d−1). Overall relative feed intake (FI = % consumption*day−1) was higher for the 20L:04D (FI = 0.81% d−1, SE = 0.06) treatment than for the 08L:16D (0.63% d−1, 0.04) and 12L:12D (0.64% d−1 0.04) treatments, whereas feed conversion efficiency (FCE = weight gain* consumption−1) was lower in the 20L:04D (FCE = 0.67, SE = 0.08) group when compared with the 08L:16D (0.88, 0.06) and 12L:12D (0.88, 0.06) treatments. Present results show that the long-term extended fixed photoperiod may act as an irritant, inducing stress, suppressing growth and reducing feed utilization. It is hypothesized that the progression of size-dependent hierarchies over time can be divided into two distinct phases herein referred to as ‘hierarchy resolution’ and ‘hierarchy stabilization’ phases (or phases 1 and 2) characterized by increasing and decreasing growth heterogeneity respectively. Growth heterogeneity is measured as coefficient of variation of weight and rank correlation of initial weight of a phase and corresponding growth rate.

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... Pichavant et al. (1998) found no growth promoting effects of an extended photoperiod on the growth of juvenile turbot over a 60-day period, nor did Hallaraker et al. (1995) for halibut over a 56day period. A long-term fixed extended photoperiod had no growth promoting effects and may have suppressed growth performance, while short-term variations in the photoperiod did not significantly affect growth in juvenile turbot (Stefansson et al., 2002). Pichavant et al. (1998) found no difference in food utilization over a 60-day photoperiod experiment. ...
... Daily protein intake, energy intake, FCR, PER, and apparent net protein retention (ANPR) were better for the extended photoperiod than for the other regimes, demonstrating that this group utilized feed more efficiently and, thus, FCR was lower. Similar results were obtained by Stefansson et al. (2002) who explained this result by possible growth-suppressing effects of a long-term, extended, fixed photoperiod on fish. In our case, fish in the 18L:6D photoperiod were less affected by extensive light intensity and, as a result, may have consumed more food. ...
... In our case, fish in the 18L:6D photoperiod were less affected by extensive light intensity and, as a result, may have consumed more food. The growth rate shared a peak with relative feed intake and conversion efficiency whereas the lowest points of these three parameters also occurred at the same times (Stefansson et al., 2002). ...
Article
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A study was conducted to determine the effect of different photoperiods on the growth and survival of juveniles of the Black Sea turbot (Psetta maeotica). Juvenile turbot (32.17±0.1 g) were reared under one of three experimental photoperiod regimes: natural, continuous light, or extended light (118 h light:6 h dark). The turbot were held in sea water (18 ppt) at 15-24°C from May 27 to July 29, 2004. The maximum growth rate, feed efficiency, and specific growth rate were recorded in the fish exposed to the extended light period (p<0.05). Continuous light may have acted as an irritant, inducing stress, suppressing growth, and reducing feed intake.
... Biswas and Takeuchi (2003) divided one cycle of 24 hours in two short periods of 12:00 h and used 6 hours of light and six hours of darkness (06:06); in this photoperiod major growth in Oreochromis niloticus was reported, due to a major consumption of feed and major efficiency of feed conversion. According to Stefansson et al., (2002), long periods of light in the turbot (Scophthalmus maximus) act as an irritant, induce stress, reduce efficiency in feed conversion and growth. In contrast, S. maximus specimens cultivated in photoperiods of 12:12 and 08:16 shown major efficiency in feed conversion, which generated an increase in the somatic growth (Stefansson et al., 2002). ...
... According to Stefansson et al., (2002), long periods of light in the turbot (Scophthalmus maximus) act as an irritant, induce stress, reduce efficiency in feed conversion and growth. In contrast, S. maximus specimens cultivated in photoperiods of 12:12 and 08:16 shown major efficiency in feed conversion, which generated an increase in the somatic growth (Stefansson et al., 2002). S. maximus was cultivated in tanks of 500 L with water recirculation system and aerobic biofilters. ...
... horas de oscuridad (06:06); en este fotoperiodo se reportó mayor crecimiento en ejemplares de Oreochromis niloticus, debido a un mayor consumo de alimento y mayor eficiencia de conversión alimenticia. SegúnStefansson et al., (2002), en el rodaballo (Scophthalmus maximus) los periodos largos de luz actúan como un irritante, inducen el estrés, reducen la eficiencia de conversión de alimento y el crecimiento. En contraste, los ejemplares de S. maximus cultivados en fotoperiodos de 12:12 y 08:16, presentaron mayor eficiencia de conversión de alimento, lo que generó un aumento en el crecimiento somático(Stefansson et al., 2002). ...
Article
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La influencia de los factores abióticos ha sido investigada extensamente en la acuacultura para controlar variables en cultivo. Se han realizado estudios para determinar la influencia (ya sea positiva o negativa) del fotoperiodo sobre diferentes etapas del ciclo de vida de algunas especies. El fotoperiodo puede condicionar la capacidad de visualización del alimento, el uso de la energía derivada de la alimentación e incluso el comportamiento social de los peces en cultivo, lo cual influye tanto en el crecimiento como en la supervivencia. El fotoperiodo también juega un papel importante en la liberación de hormonas reproductivas y la expresión de genes que estimulan el desarrollo sexual, lo cual influye directamente en la reproducción de los peces. El objetivo de la presente revisión fue investigar la influencia del fotoperiodo en distintas especies de peces cultivados comercialmente en diferentes sistemas de cultivo experimentales.
... In other flatfish species, there are indications that exposure to continuous light during the juvenile stage may significantly affect subsequent growth and age at maturity (Imsland and Jonassen, 2003, 2005; Imsland et al., 2009). However, in some cases prolonged exposure to continuous or extended light regimes may reduce growth and food conversion efficiency (e.g. Stefánsson et al., 2002), so the period of extended or continuous light must be synchronised with the internal rhythms of the fish in order to achieve increased growth and/or lower maturity. Interpretation of environmental cues and control of reproductive timing are mediated by the brain–pituitary–gonad (BPG) axis (Nagahama, 1994; Bromage et al., 2001; Weltzien et al., 2003). ...
... Following transfer between LD16:8 to LD24:0 feed conversion efficiency was up to 16% higher in the LD16:8 group compared to the " transfer " groups where FCE was measured (Groups 2A and 2B) during the laboratory trial. Stefánsson et al. (2002) exposed juvenile turbot to three photoperiods (LD20:4, LD12:12 and LD8:16) for a period of approximately 9 months. Fish exposed to LD20:4 displayed the lowest overall growth rate (0.77% day −1 ) and the lowest FCE (0.67), but the highest overall feed intake. Fish exposed to LD12:12 performed best, with SGR amounting to 0.82% day −1 , wh ...
Data
A group of juvenile turbot (mean (SE), initial weight 22 g (1.5)) were reared in indoor and covered outdoor tanks under ambient temperature conditions for 46 months until harvest (mean final weight, 2.7 kg). The photoperiod treatment was divided into 5 phases where the fish in each phase were exposed to either 16 h of light and 8 h of darkness (LD16:8, extended light, E) or continuous light (C). Thus, the following five photoperiod combinations were tested: a) LD16:8 (Control) group (EEEEE), b) Group 2A (ECEEE), c) Group 2B (EECEE), d) Group 2C (EEECE), and e) Continuous light (CCCCC). Long term rearing on continuous light reduced growth, whereas short term exposure to continuous light stimulated growth as the final mean weights of Groups 2C and 2B were 16 and 11% higher than those of the Control and the Continuous light groups. Significantly higher male plasma 11-ketotestosterone levels were seen in the Control group in July 2011 (5.67 ng mL −1) and June 2012 (2.56 ng mL −1) than in the other experimental groups, indicating delayed maturity in groups reared under continuous light. Estradiol 17-β levels were low in all groups throughout the experiment indicating low or no female maturation. Photoperiod regime had only minor effect on flesh quality traits of the fish. Based on current results, we recommend that turbot is farmed at extended light (i.e. LD16:8) in combination with continuous light during spring and summer (i.e. Group 2C in this study) during the second production year.
... An intense and prolonged light can be annoying and harmful to fishes, indirectly affecting physiological parameters regarding to energy expenditure, then acting as a stressor (Boeuf & Le Bail, 1999;Stefánsson et al., 2002;Almazán-Rueda et al., 2005). If increased light can reduce fish"s aggressive behavior, it would be a strategy to reduce energy expenditure caused by metabolic changes resulting from potentially stressful environmental changes (Carvalho et al., 2012). ...
... According to Boeuf & Le Bail (1999) and Stefánsson et al. (2002), the prolonged and very intense light can be annoying and harmful to the fishes. Although the light intensity can be considered a stressor for these animals, this response was not observed with the analysis of catalase activity. ...
Chapter
The demand for attributes beyond quality, such as food safety, respect for the environment and production with social responsibility is increasing in world food trade. In parallel, the fish production chain has been confronted by problems with the lack of quality of their products, many of them related to the quality of the cultivation or capture waters. Nowadays, the water where these organisms are created, presents itself as a critical control point, as well as influencing the quality / safety of the product, the cultivation should be done in an environmentally sustainable manner. In this sense, the fish has been shown to be responsible for public health problems, such as scromboid poisoning, toxicity by mollusks, ciguatera and microbial contamination or through toxic metals such as mercury. Besides the aspects of security and environmental sustainability, the relationship between water quality and the occurrence of compounds capable of negatively alter the taste and smell of fish (off flavoUr) has been evidenced in many studies. For crop species there is the possibility of controlling the quality of the fish through the proper management, which primarily begins with the quality of the cultivation water. However, questions regarding the best handling practices, processing, storage and marketing also have troubled the consumer, who is more attentive to issues of food safety and quality programs, being, in some cases, willing to pay more for a product of best quality, convenience and posing no danger to their health, the environment or society. It is noted that the tilapia is a species that can guarantee the availability of fish in many regions, since its cultivation has been successful. The advantages of tilapia farming, in relation to other species, are in the easy feeding, hardiness, prolificacy and good adaptation. Based on the chain of production of fish, although the meaning of quality is broad, standing out in this concept features that the consumer believes that the product should have, or should approach its intrinsic composition, nutritional value, likely to change during the preparation, storage, distribution, sale and presentation to the consumer. Specific actions of environmental and ecological nature should be proposed, with the aim of contributing to the sustainable and rational exploitation of resources, and minimizing the adverse impact that the waste generated by this activity produces on the environment; seeking responsible and sustainable management of fish agribusiness.
... An intense and prolonged light can be annoying and harmful to fishes, indirectly affecting physiological parameters regarding to energy expenditure, then acting as a stressor (Boeuf & Le Bail, 1999;Stefánsson et al., 2002;Almazán-Rueda et al., 2005). If increased light can reduce fish"s aggressive behavior, it would be a strategy to reduce energy expenditure caused by metabolic changes resulting from potentially stressful environmental changes (Carvalho et al., 2012). ...
... According to Boeuf & Le Bail (1999) and Stefánsson et al. (2002), the prolonged and very intense light can be annoying and harmful to the fishes. Although the light intensity can be considered a stressor for these animals, this response was not observed with the analysis of catalase activity. ...
... The feed intake of fish exposed to the continuous light (LD24:0) regime was significantly higher (P < 0.05) than that of fish in the other 3 groups. The LD0:24 group consistently had the lowest feed intake (P < 0.05), as also mentioned by Boeuf and Le Bail (12) and Stefansson et al. (6). A decreased growth rate has been observed when the photoperiod regime was kept shorter than the natural (19,20). ...
... SGR and FCR were significantly lower in fish exposed to the LD0:24 photoperiod regime. This was also observed in the studies by Imsland et al. (4) and Stefansson et al. (6). ...
Data
Full-text available
The effects of 4 different experimental photoperiod regimes, LDN (natural photoperiod), LD24:0 (24 h light:0 h dark), LD12:12 (12 h light:12 h dark) and LD0:24 (0 h light:24 h dark), on feed intake and growth parameters of juvenile turbot (21 ± 2.3 g) in the Black Sea were determined. Growth was highest in the group exposed to the continuous photoperiod (LD24:0), followed by the LD12:12, LDN and LD0:24 groups in descending order. The lowest growth rate was recorded in the LD0:24 group. According to the results obtained, LD24:0 and LD12:12 photoperiod exposures are best for better growth and food conversion in juvenile turbot.
... The growth-enhancing effect of extended photoperiod in these studies is subtle compared to that observed in salmonids (Stefansson et al. 1989; 1991; Solbakken et al. 1994). Moreover other studies have concluded that there are no or only limited effects of extended photoperiod on growth in halibut (Hallaråker et al. 1995) and turbot (Pichavant et al. 1998; Stefánsson et al. 2002). Pichavant et al. (op cit.) exposed juvenile turbot to four constant and two changing photoperiod regimes in a 60-day experiment and found no difference in either growth performance or food utilization. ...
... Pichavant et al. (op cit.) exposed juvenile turbot to four constant and two changing photoperiod regimes in a 60-day experiment and found no difference in either growth performance or food utilization. Similar finding were reported by Stefánsson et al. (2002) in 297-day experiment where juvenile turbot were reared at three constant photoperiods (8 h light:16 h darkness, LD8:16; LD12:12 and LD20:4). The group reared at LD12:12 displayed higher growth and better food conversion efficiency and the authors hypothesize that long-term extended fixed photoperiod may suppress growth and feed utilization by acting as a stressor. ...
Article
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The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut Hippoglossus hippoglossus and in 114 (50 females and 64 males) individually tagged turbot Scophthalmus maximus. The halibut were reared at 11 °C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light 4 May 1996 (LD8:16–24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16–24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. The turbot were reared at 16 °C on three different light regimes: constant light (LD24:0), 16 h light:8 h darkness (LD16:8), or simulated natural photoperiod (LDN). After 6 months on the different photoperiods, the turbot was reared together on LDN for approximately 12 months until first maturation. Juveniles subjected to continuous light (halibut) or extended photoperiods (halibut and turbot) exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, when the photoperiod increased naturally with day-length or when fish were abruptly switched from being reared on short-day conditions to continuous light, a subsequent increase in growth rate was observed. This growth enhancing effect of extended photoperiods was more apparent on a short time scale in Atlantic halibut than in turbot, but both species show significant long-term effects of extended photoperiods in the form of enhanced growth. In both species lower maturation of males was seen in groups exposed to extended or continuous light compared to LDN and this could be used to reduce precocious maturation in males leading to overall increase in somatic growth.
... However, in some cases prolonged exposure to continuous or extended light regimes may reduce growth and food conversion efficiency (e.g. Stefánsson et al., 2002), so the period of extended or continuous light must be synchronized with the internal rhythms of the fish in order to achieve increased growth and/or lower maturity. Studies on Atlantic cod Gadus morhua L. have shown that constant light in indoor systems throughout the juvenile stage has a growth-promoting effect and reduces the incidence of maturation in indoor tanks (Hansen et al., 2001). ...
Article
From an aquaculture point of view, control of the sexual maturation cycle is critical for a sustainable production of the species. For year-round reliable production of juvenile lumpfish of the appropriate size for stocking salmon cages, there is a need for basic and applied knowledge on the control of sexual maturation in cultured lumpfish broodstock. Lumpfish (initial size 219 g and 16.9 cm) were reared under advanced simulated natural photoperiod (SLDN, control group) for Tromsø (70°N). In addition there were two groups exposed to continuous light from April 2014 to January 2015 (PP3) and from April 2014 to April 2015 (PP6) followed by 8 week decline in hours of light from 24 to 4 h (autumn signal) and subsequent 8 week rise from 4 to 24 h (spring signal). Exposure of lumpfish to continuous light followed by an autumn-spring signal stimulated somatic growth and affected age at first maturity in females. The growth enhancing effect of continuous light lasting for approximately six months in females compared to one month in the males. Spawning colouration and running milt was seen in males in all three photoperiod groups from September 2014 onwards indicating that maturation started prior to the experimental treatment. In the females spawning time, egg volume and hatching success varied between the photoperiod groups. No spawning occurred in the SLND group, whereas spawning was seen in both PP female groups 3–6 months after the onset of short autumn-short spring photoperiodic signal. Hatching success was higher in the PP3 group (83.4%) compared to the PP6 group (72.3%). The current findings are the first step in the development of photoperiod regimes which may provide simple and effective off-season maturation in lumpfish.
... On the other hand, the absence of significant correlations in fish reared without substrate coupled with the increased aggressive behaviour observed may indicate an unstable social environment where fish are fighting for a high position in the hierarchy, despite the rather long rearing period (98 days). Although it has been previously reported that a specific social hierarchy, within a newly composed fish group, is established within a few days (Winberg and Nilsson, 1993b;Goldan et al., 2003), longer than 90 days hierarchical resolution phase has also been observed for flatfish species (Stefánsson et al., 2002;Overton et al., 2010). Table 1 Pearson correlation coefficients (r) between brain neurotransmitters and final body mass for gilthead seabream reared with blue (BS), red-brown (RBS) substrate or no-substrate (C) under two different densities (D, 2D) for 98 days. ...
Article
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The presence of blue or red-brown substrate on tank bottom has been previously reported as an efficient means of environmental enrichment for gilthead seabream. The present study aimed to investigate whether this enrichment is still beneficial when gilthead seabream is reared under different social conditions (i.e. a lower 4.9kgm(-3) and a higher 9.7kgm(-3) density). Water exchange was adjusted according to fish biomass to exclude density effects on water quality. In the enriched tanks single-colour glass gravel was used as substrate (Blue and Red-Brown substrate, or BS and RBS respectively), while control tanks had no gravel. Growth, aggressive behaviour and size distribution results indicated that the lower density created a less favourable social environment. In both densities studied, BS enhanced growth, suppressed aggression and reduced brain serotonergic activity. In the condition of intense social interactions (i.e. the lower density) BS also reduced brain dopaminergic activity. These results along with the negative correlations observed between brain monoamines and fish body mass, indicated that substrate and density effects are socially-induced. However, there may be several biotic and/or abiotic factors interfering with substrate effects that should be investigated before the practical use of a substrate in land-based intensive aquaculture.
... However, in some cases prolonged exposure to continuous or extended light regimes may reduce growth and food conversion efficiency (e.g. Stefánsson et al., 2002), so the period of extended or continuous light must be synchronized with the internal rhythms of the fish and the season in order to achieve increased growth and/or lower maturity. Based on findings from other marine species and the recent study of Imsland et al. (2018) we hypothesize that rearing juvenile lumpfish at continuous light will enhance growth during the late juvenile phase. ...
... 1.00), but this might be purely contextual. Other tests should be undertaken in other rearing contexts and factors that have been demonstrated to affect growth heterogeneity, such as temperature, photoperiod, water velocity, daily food ration and stocking density Jobling and Baardvik, 1994;Ryer and Olla, 1996;Fontaine et al., 1997;Stefansson et al., 2002). ...
Article
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This study aimed at modeling the relative importance of food intake on growth heterogeneity among cultured sea bass (Dicentrarchus labrax). First, we designed an individual growth model comprising five compartments (Energy intake, Losses, Net Energy, Recovered Energy and Maintenance). This model was calibrated with a first experiment carried out in eight tanks; A total of 130 juveniles (11 g) per tank were fed by a self-feeder (84 days, 20°C, 16L : 8D, 30 g NaCl/l). A second experiment was performed to better understand the relation between individual food intake, individual growth and growth heterogeneity, using the model as a tool for a hypothetico-deductive approach on growth heterogeneity (135 passive integrated transponder-tagged fish, same rearing conditions as above and individual food intake measured by X-ray every 14 days). The tested hypotheses were that food intake was (a) homogeneous, (b) proportional to the fish weight (i.e. to W1.00) X-ray (c) proportional to W0.66 and (d) reflected by the X-ray measurements of food intake. For each hypothesis, a simple linear regression between experimental and simulated results was produced. The Fitness indicators of these analyses, together with their confidence intervals (calculated by bootstrapping), allowed testing the relevance of these hypotheses. The analysis indicated that growth heterogeneity was largely accounted for by individual variations of food intake, as revealed by the X-ray analysis, and that food intake was proportional to W1.00, which suggests a dominance hierarchy where small fish are incapable of feeding maximally.
... In juvenile turbot Scophthalmus maximus, an extended photoperiod was found to enhance growth in some experiments (Imsland et al. 1995, 1997), while others found that it induced chronic stress, which inhibited fish growth (Stefànsson et al. 2002). In juvenile Atlantic halibut Hippoglossus hippoglossus, growth enhancement was obtained after fish were transferred from a natural photoperiod to continuous light (Simensen et al. 2000; Imsland et al. 2006). ...
Article
In age-0 winter flounder Pseudopleuronectes americanus, a fixed long photoperiod (14.5 h light : 9.5 h dark) applied during the first 45 d postsettlement did not improve growth compared with fish held under natural photoperiod conditions. After being reared under these two regimes until 29 October, juveniles exposed to the long photoperiod after settlement were maintained under the same conditions during the winter, but temperature was not allowed to decrease below 4◦C. Juveniles previously exposed to the natural photoperiod were maintained under one of the following conditions: (1) natural photoperiod and natural temperature (1–9◦C), (2) natural photoperiod and a minimum winter temperature of 4◦C, or (3) long photoperiod and a minimum temperature of 4◦C. Most mortality (80%) occurred within the first 2 months of the experiment. Juveniles that experienced the transition from natural to long photoperiod conditions displayed higher growth through the winter than did juveniles exposed to natural conditions; at the end of winter, fish that were transitioned to the long photoperiod were 25% longer (19 mm), were twice as heavy (125 mg), and contained twice as much total lipids (803 μg/mg) and five times more triacylglycerols (24% of total lipids) than juveniles subjected to the natural photoperiod. These results indicate that we may be able to eliminate the winter fasting that occurs under natural conditions and to elicit winter growth in this species by using photoperiod manipulation. In addition, it appears that a decrease in photoperiod is needed for fish to respond to a subsequent increase in photoperiod.
... Quest'ultimo è stato regolato in modo da ottenere un fotoperiodo di 12 ore di luce e 12 di buio in quanto numerosi studi hanno dimostrato che in tali condizioni l' accrescimento e l' utilizzazione di cibo da parte dei soggetti risulta maggiore rispetto ai risultati ottenuti con altri fotoperiodi (Stefanson et al., 2002). ...
... Duston, Astakie, and MacIsaac (2003) found a significant increase in the proportion of higher value immature Arctic charr by applying a long photoperiod (18L:6D) for 42 days in winter followed by a short or natural photoperiod compared with fish reared on constant long day or natural photoperiod. In contrast, long-term exposure to continuous or extended light regimes has, in some cases, resulted in reduced growth and food conversion efficiency (Stefánsson, FitzGerald, & Cross, 2002), implying that the period of extended or continuous light must be harmonized with the internal rhythms of the fish in order to achieve optimal results. The present study was set up to investigate the effect of periodic exposure to continuous light at different phases during the winter on growth and subsequent maturation in Arctic charr. ...
Article
Full-text available
The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming.
Article
The aim of the present study was to investigate possible stressful effects on European sea bass Dicentrarchus labrax reared under constant darkness (0L-24D) and to examine the possible anti-stressful effect of dietary tryptophan (TRP) supplementation. Juvenile European sea bass (initial body weight 4.23 ± 0.032 g) were reared for 10 weeks under 0L-24D and 12L-12D and fed either a commercial diet (0.47% TRP) or the same diet supplemented with L-TRP (2.47% TRP). Results showed that lighting conditions had no significant effect on fish growth, while a depressive effect by the TRP supplementation was obvious. All fish populations reared under 0L-24D exhibited reduced body protein, lipid and ash content and increased food consumption. Reduced body lipids, food consumption and nutrient utilization were observed in TRP-supplemented fed fish, along with lower liver lipids. Dietary TRP enrichment significantly lowered liver saturated and monounsaturated acids and increased poly- and highly-unsaturated fatty acids, especially in combination with 0L-24D. These changes were also considerably reflected in carcass fatty acid composition.
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A 3-month study was carried out to investigate the effects of grading on the overall production, growth performance and survival of juvenile Dover sole (Solea solea L.). Juvenile fish (4.0–40.4 g) were sorted into three size groups: small (4.0–15.5 g), medium (16.0–21.5 g) and large (22.0–40.5 g). In addition, a group of unsorted fish was followed for comparison. The fish from each sorted group and the unsorted group were divided between triplicate tanks at a stocking density of 1.5 kg m−2. The fish were weighed and counted 21, 42, 63 and 92 days after stocking. In addition, 30 randomly chosen fish in each tank (=90 from each group) were individually tagged. The survival, size distribution, growth and productivity were calculated for small, medium, large and unsorted groups. In addition, comparisons were made between combined sorted and unsorted fish. There was no significant difference between the mean weight and distribution of sorted and unsorted fish by the end of the trial. An increased overall productivity in combined sorted fish was observed. Regular grading could therefore still be beneficial for sole farming as long as the grading interval supports maximum growth (in this case over 90 days). Survival was not significantly affected by the grading process.
Article
Juvenile Atlantic halibut, Hippoglossus hippoglossus (initial weight (SD) 191.3 (±44.7)) g, were reared for 99 days at a constant temperature of 11°C and subjected to three different light regimes from 13 September to 21 December: continuous light (LD24:0), simulated natural photoperiod of Bergen (60°25′N, LDN) and constant 20 h light:4 h dark (LD20:4). The fish reared on the different photoperiod regimes differed in their growth patterns as juveniles exposed to long days, i.e. LD20:4 and LD24:0, exhibited faster growth than those experiencing a natural photoperiod. The LD20:4 group showed the highest average specific growth rate (0.72% body weight day−1), whereas fish on LDN displayed the lowest average specific growth rate (0.60% body weight day−1). The final mean weights of the LD20:4 and the LD24:0 groups were 15% and 12% higher than those of the LDN group. Dividing the duration of the experiment into three time periods shows that the LD20:4 and LD24:0 had a higher feed conversion efficiency (FCE) as compared with the LDN group during the first and the last period, while a reversed situation was observed in the second period. Our data indicate a larger variation in growth rates among individuals in the best-performing groups (here LD20:4 and LD24:0). This may indicate that formation of size hierarchies is more pronounced in groups with more homogenous growth (here LDN). Overall, our findings indicate that extended light regimes result in faster growth and better feed conversion in juvenile Atlantic halibut. In line with findings on other flatfish species, this supports the concept that constant long day:short night or continuous light regimes should be used by the farmer in order to maximize growth and improve feed conversion in Atlantic halibut.
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The aim of this study was to investigate the effect of continuous light at different stages during the production cycle of Atlantic halibut Hippoglossus hippoglossus L. on growth, age at first maturity, endocrine parameters and flesh quality. A group of juvenile halibut [mean (SD), initial weight 191.3 g (44.7)] was reared in indoor tanks under ambient temperature conditions for 38 months until harvesting (mean final weight, 4.6 kg). The entire photoperiod experiment was divided into four phases, where the fish in each phase were exposed to either natural photoperiod (62°33′N) or continuous light (L). Thus, the following five photoperiod combinations were tested: (a) Control group (NNNN), (b) Group 2A (NLNN), (c) Group 2B (NNLN), (d) Group 2C (NNNL) and (e) Production group (LNNN). Exposure to continuous light stimulated growth, and the final mean weights of Groups 2A and 2B were 23% and 11% higher than those of the Control group (NNNN). The final plasma 11-ketotestosteron levels were lower in Groups 2A (2.94 ng mL−1) and 2B (2.46 ng mL−1) compared with the Control (5.29 ng mL−1), Group 2C (5.09 ng mL−1) and the Production group (4.78 ng mL−1) during spring 2007 (age 4 years), indicating higher age at first maturity in Groups 2A and 2B. Photoperiod regime had only a minor, and transient, effect on flesh-quality traits of the fish, whereas a significant seasonal effect was seen with a tendency towards increased gaping, lower pH, lower hardness and lower shear force in July compared with December and March.
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The effects of 4 different experimental photoperiod regimes, LDN (natural photoperiod), LD24:0 (24 h light:0 h dark), LD12:12 (12 h light:12 h dark) and LD0:24 (0 h light:24 h dark), on feed intake and growth parameters of juvenile turbot (21 ± 2.3 g) in the Black Sea were determined. Growth was highest in the group exposed to the continuous photoperiod (LD24:0), followed by the LD12:12, LDN and LD0:24 groups in descending order. The lowest growth rate was recorded in the LD0:24 group. According to the results obtained, LD24:0 and LD12:12 photoperiod exposures are best for better growth and food conversion in juvenile turbot.
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The effect of stocking density and photoperiod on Hippocampus abdominalis was examined in this study. Stocking densities of 45, 30, 15 and 5 seahorses 3 L−1 were tested on newborns. Growth and survival were independent of stocking density. A second stocking-density experiment aimed to remove the effect of an early mortality experienced in experiment 1 using older juveniles at 25, 15 and 5 seahorses 3 L−1. There were no differences in the parameters measured. Also, the effect of photoperiod was investigated on seahorses cultured under 24:00, 16:08 and 08:16 (L:D) photoperiods. A single Artemia meal was delivered at 10:00 hours. Survival and body growth in 16:08 and 08:16 hours were higher than in 24:00 hours. In a second experiment, seahorses were cultured in the photoperiods and conditions described for experiment 1, except they were fed twice the amount in two meals delivered at 10:00 and 16:30 hours. The seahorses in 16:08 hours showed better growth than the other treatments, but there were no differences in survival. These results suggest that early juvenile H. abdominalis can be cultured at higher stocking densities than previously reported, without compromising growth and survival, and when feeding was not limiting, grew better in an extended photoperiod (16:08) but not in 24:00 hours.
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The effect of four different light regimes on growth was studied in lenok, Brachymystax lenok. Fish with average weights of 5.5 g were subjected to four different photoperiods (0L:24D, 6L:18D, 12L:12D and 24L:0D) for 35 days. The specific growth rate (SGR) of lenok in 24-h darkness had a significantly higher SGR than those in the continuous light regime (P < 0.05); however, there was no significant difference among fish exposed to 6L:18D, 12L:12D and 24L:0D photoperiods. There was a tendency for higher food intake over the light period extension from 0L to 24L, and feed intake was significantly higher in the continuous light group than in 24-h darkness (P < 0.05). No significant difference in feed conversion efficiency (FCE) was observed between fish exposed to 0L:24D and 6L:18D photoperiods, however, the FCE in both photoperiods was significantly higher than that in the other two groups. The final survival rate of juveniles varied from 79.67 to 95.33%, with significant differences among experimental groups. Fish tested in continuous illumination spent much more energy on respiration and excretion while depositing less energy for growth than in the other photoperiods. In contrast, fish in 24-h darkness deposited more energy for growth and spent less energy on respiration and excretion. Results show that photoperiod manipulation can affect growth, and that a continuous dark regime could improve growth in lenok at this stage of development.
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Juvenile blunt snout bream Megalobrama amblycephala were reared under three photoperiods, 8 L: 16D, 12 L: 12D and 16 L: 8D (L: light; D: dark) for over 8 weeks. The results showed that growth performance was significantly enhanced by long photoperiod. Contrary to feed conversion ratio, final length, final weight, weight gain and feed intake increased significantly as illumination time increased from 8 h daily to 16 h daily. Low size heterogeneity and whole-body lipid content in fish exposed to long photoperiod were also observed. Both relative mRNA expression level of GH and IGF-I increased as illumination time increased from 8 h to 16 h daily. The lowest value of plasma cortisol was observed at the middle the photophase while the highest value was observed at the transition between the day and night span. Hepatic MDA content significantly increased as illumination time increased from 8 h daily to 16 h daily. The activities of hepatic catalase and glutathione peroxidase were lowest in fish exposed to 16 L: 8D photoperiod and significantly lower than that in fish exposed to 8 L: 16D. These results indicate that photoperiod manipulation may not only improve growth performance but also reduce size heterogeneity. However, prolonged photoperiod could cause chronic stress since plasma cortisol level was higher in the long photoperiod group, leading to an increasing oxidative stress.
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Evaluation of anchovy as a feed for turbot (Psetta maeotica). In this study, the effects of feeding young turbot (Psetta maeotica) with either dry pellet (50% crude protein and 18% crude oil), fresh anchovy (Engraulis encrasicholus; 20.8% crude protein and 9.2% crude oil) or combination of both on growth and feed efficiency rate (FCR) were investigated. A total of 90 turbot fry (15 fish per tank) with a mean of initially weight of 41 g were used. At the end of 45 day, the mean weights of fish with dry pellet (PL), fresh anchovy (HS) or combination of both (HP) were 62,30 ± 2,22 g, 63,54 ± 1,89 g and 62,90±0,89 g, respectively. No significant differences were observed among treatments (P>0.05). Daily food consumption (g dry feed/ g fish weight) and FCR (g dry feed/g weight gain) values for as follows: 0,77±0,01 ve 0,86±0,07for PL, 0,78±0,01 ve 0,82±0,09 for HP, and 0,75±0,02 and 0,79±0,06 for HS. There were no differences between any treatments (P>0.05). Our findings indiciated that of feedings turbot with HP, PL and HP had similar effects on growth and FCR. Turbot can be fed either dry pellet or fresh anchovy or combinating of both. Özet: Bu araşt ırmada, pelet yem (%50 ham protein ve % 18 ham yağ), taze hamsi (Engraulis encrasicholus; %20,8 ham protein ve %9,2 ham yağ) veya her iki yemle beraber beslemenin, kalkan bal ığ ı (Psetta maeotica) yavruların ın büyüme ve yem değerlendirme üzerine etkisi incelenmiştir. Üç farkl ı diyetin iki tekerrürlü olarak incelendiği bu çal ışmada, ortalama ağ ırl ığ ı 41 g olan toplam 90 adet kalkan bal ığ ı yavrusu (15 adet/tank) kullan ılm ışt ır. 45 gün süren deneme sonunda, gruplardaki ortalama bal ık ağ ırl ıkları sadece peletle beslenen grupta (PL) 62,30±2,22 g, hamsi ve peletle yemlenen grupta (HP) 63,54±1,89 g ve sadece hamsi ile beslenen grupta (HS) 62,90±0,89 g olarak tespit edilmiştir. Gruplar aras ındaki fark istatistiki olarak önemsiz bulunmuştur (P>0,05). Günlük yem tüketimi (%, g kuru yem/ g bal ık ağ ırl ığ ı) ve yem değerlendirme değerleri (g tüketilen kuru yem/g ağ ırl ık art ış ı) PL grubunda 0,77±0,01 ve 0,86±0,07, HP grubunda 0,78±0,01 ve 0,82±0,09 ve HS grubunda 0,75±0,02 ve 0,79±0,06 olarak tespit edilmiş ve gruplar aras ında fark bulunmam ışt ır (P>0,05). Araşt ırma sonuçlarına göre, kalkan bal ığ ı yetiştiriciliğinde farkl ı besleme uygulamaların ın büyüme ve yem değerlendirme üzerinde benzer etki gösterdiği görülmüş ve bal ıkların beslenmesinde sadece pelet yem, sadece hamsi veya pelet yemle birlikte taze hamsi verilebileceği sonucuna varılmıştır.
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Juvenile turbot Psetta maxima(Linnaeus, 1758) (15.23 ± 2.99 g) were fed to satiation with a commercial extruded feed over a 60-day period. Feeding regimens were twice a day (TD), every other day (EOD), and 2-day intervals (TDI). Fish were kept in seawater (18 ppt) at 5-7.5°C from January 21 to March 23, 2004. Feed conversion rate (FCR) and the protein efficiency ratios (PER) were within the ranges of 1.12-1.14 and 2.26-2.29, respectively. While the maximum relative growth rate (RGR), weight gain, and specific growth rate (SGR) were recorded in the TD group, they were lower in the EOD and TDI groups. Both the SGR and RGR increased as feeding frequency increased. The feeding frequency influenced the chemical composition of the fish. Lipid and protein content of the fish increased in the TD group. In terms of SGR and RGR, it can be concluded that the best growth rates of Black Sea turbot cultured at 5-7.5°C were obtained from the fish in the TD and EOD groups.
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In this study, the effects of feeding young turbot (Psetta maeotica) with either dry pellet (50% crude protein and 18% crude oil), fresh anchovy (Engraulis encrasicholus; 20.8% crude protein and 9.2% crude oil) or combination of both on growth and feed efficiency rate (FCR) were investigated. A total of 90 turbot fry (15 fish per tank) with a mean of initially weight of 41 g were used. At the end of 45 day, the mean weights of fish with dry pellet (PL), fresh anchovy (HS) or combination of both (HP) were 62,30 ± 2,22 g, 63,54 ± 1,89 g and 62,90±0,89 g, respectively. No significant differences were observed among treatments (P>0.05). Daily food consumption (g dry feed/ g fish weight) and FCR (g dry feed/g weight gain) values for as follows: 0,77±0,01 ve 0,86±0,07for PL, 0,78±0,01 ve 0,82±0,09 for HP, and 0,75±0,02 ve 0,79±0,06 for HS. There were no differences between any treatments (P>0.05). Our findings indiciated that of feedings turbot with HP, PL and HP had similar effects on growth and FCR. Turbot can be fed either dry pellet or fresh anchovy or combinating of both.
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Wild populations of the green mojarra Cichlasoma beani, are being pressured by anthropogenic activities. It is possible to mitigate the deterioration of native species populations by developing culture techniques. Environmental factors such as light intensity and photoperiod may affect the development of fish under culture conditions. Therefore, the aim of the present study was to examine the effect of these factors on growth, survival, and condition of C. beani cultured in different light intensities and photoperiods. Light intensities of 1000, 1500 and 2000 lux and photoperiod 24:00, 16:08 and 08:16 Light:Dark (L:D) were tested in 40 L tanks (10 fish per tank, three replicates per treatment) during eight weeks. There were no significant differences in light intensity or photoperiod, which was associated with the natural adaptation of the species to these factors. The results also suggested the favorable overall growing conditions during the trial and he response of the life cycle stage of the specimens used in this study. The results of the present study indicate that the natural adaptations of C. beani, allow the favorable culture in various light conditions in juveniles, which can be advantageous for commercial culture as may imply low energy costs.
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Dominance relationships between pairs of Atlantic salmon parr of known size were assessed at various times during their first year of life. In tests conducted between first feeding and early July, the larger of two fish was dominant in only 54% of pairs, regardless of the magnitude of the size difference between the fish. In September, there was a stronger association between size and status, especially in pairs with a large size differential, where the dominant was larger in 72% of cases. In groups of parr tested in April of the following year, there was no relationship between size and status, the larger of two fish being dominant in 48% of cases, regardless of the magnitude of the size differential. This result suggests that status in early social interactions may depend on behavioural properties rather than size and that the larger size of dominant fish reported in a number of salmonids might be a consequence and not a cause of high status.
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The majority of fish farmers and aquaculture researchers are aware that aggressive behaviour and high levels of competition within a group of fish can have serious consequences for growth. Nevertheless, only rarely have attempts been made to assess the influences of social interactions upon the growth of farmed fish. The collection of detailed information about social behaviour is time consuming, and the techniques used (e.g. direct observation or video recording) are best suited for obtaining information about individuals held in small groups, and so the study of the social environment of fish has largely remained the domain of the behavioural ecologist (Thorpe and Huntingford,
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Although high stocking densities of turbot have been achieved in culture using supplementary oxygenation, this rearing strategy ignores the possibility that high densities may interfere with behavioural interactions between individuals and thereby affect biomass gain. This study describes the effect of stocking density on the growth of juvenile turbot populations. Groups of juvenile turbot were reared at four different densities (initial densities: 0.7, 1.1, 1.5 and 1.8 kg/m2) for 45 days. Treatment density had a significant effect on turbot growth rates over the experimental period. Fish held at the highest density showed lower growth rates and mean weights at the conclusion of the study than fish held at lower densities. The dispersion in fish weights was also affected by stocking density. The variation in fish weights was greatest in the highest density group and as stocking densities increased the growth of some individuals was suppressed. It is concluded that growth of juvenile turbot can be significantly increased and more homogeneous weights achieved by stocking the fish at lower densities than previously reported.
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Light compares a complex of external and ecological factors, including colour spectrum, intensity and photoperiod. Light characteristics are very specific in an aquatic environment and light is extremely variable in nature. `Receptivity' of fish to light profoundly changes according to the species and the developmental status. Specific photoreceptor cells are present in both eye and pineal. If it is easy to change the light in experimentation and to observe the effects on fish growth, it is much more difficult in nature to make such determinations. In larvae, many studies have been dedicated to the influence of intensity and photoperiod on growth: generally, species need a minimal threshold intensity to be able to develop normally and grow. This is probably related to the aptitude to localize, catch and ingest prey. Light is also indispensable for body pigmentation, an important phenomenon involved in early development and growth. Too intense light can be stressful or even lethal. A few species are able to develop and grow at very low intensities or, sometimes, in the absence of light. Generally, long daylength improves larval rearing quality. The synergistic effect of `food availability-daylength' appears to be determining at this stage. In older fish, there is very little information about the influence of light `quality' but more about intensity and much more about photoperiod. Light intensity effects are not so clear and depend on the species and the experimental procedures: it is probably not an important factor for growth stimulation. Daylength appears much more important. Many species, including both marine species and salmonids, react to photoperiod treatments and long daylength stimulates growth. The most studied species is the Atlantic salmon, which is very sensitive, both during the freshwater stage, with the parr–smolt transformation very dependent on the photoperiod, and also in sea water. In this last condition, lighting also influences early maturation. An important point is to be certain that light affects fish growth through a better food conversion efficiency and not just through stimulated food intake. Also included in this review is a discussion about the endolymph–otolith system, which is very sensitive to daylight and seasonal cycles and a review of the present knowledge on the involvement of light influence on hormone levels (melatonin, somatotropin, thyroid hormones and other hormones).
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Growth rate of tagged juvenile turbot was significantly influenced by the interaction of temperature and fish size. The results suggest the optimum temperature for growth of juvenile turbot in the size range 25-75 g is between 16 and 19° C. Optimal temperature for growth decreased rapidly with increasing size, and is between 13 and 16° C for 100 g turbot. Although individual growth rates varied highly at all times within the temperature treatments, significant size rank correlations were maintained during the experimental period. The study confirms that turbot exhibit ontogenetic variation in temperature optimum, which might partly explain different spatial distribution of juvenile and adult turbot in ocean waters.
Article
Alternative formulations of Levene's test statistic for equality of variances are found to be robust under nonnormality. These statistics use more robust estimators of central location in place of the mean. They are compared with the unmodified Levene's statistic, a jackknife procedure, and a χ2 test suggested by Layard which are all found to be less robust under nonnormality.
Article
The growth rates and food conversion efficiencies of juvenile normally pigmented turbot, malpigmented turbot and turbot-brill hybrids were measured at 10°C and 14°C. The survival rate over the 120-day experimental period was 96%. Results showed no evidence of hybrid vigour (heterosis), and in fact significantly higher growth rates were observed in turbot. All three types of fish grew faster at the higher environmental temperature due mainly to a much improved appetite, but also perhaps due to an increase in the food conversion efficiency. Malpigmented turbot appeared particularly well suited to the conditions associated with intensive culture and exhibited the highest growth rates at both 10 and 14°C. For malpigmented turbot at 14°C the mean growth rate was 2.17% per day.
Article
This chapter discusses the analysis of repeated measurements from a multivariate analysis of variance point of view. The generalization of the analysis of variance procedure to analyze repeated measurement designs utilizing the multivariate analysis of variance approach employs the multivariate general linear model and the testing of linear hypotheses using p-dimensional vector observations. In many applications of repeated measurement designs, subjects receive treatments in low-order factorial combinations, where the sequence of administration is randomized independently for each subject. Designs with multivariate observations on p variates over q conditions are called “multivariate” or “multi-response repeated measurement designs” because the multivariate observations are not commensurable at each treatment condition, but are commensurable over conditions a variable at a time. The chapter discusses the one-sample repeated measurement design, I-sample repeated measurement design, crossover/changeover design, and growth curve analysis. In the analysis of the one-group repeated measurements design from a multivariate analysis of variance point of view, no restrictions are placed on the structure of the variance-covariance matrix Σ. While the standard multivariate analysis of variance (MANOVA) model (SMM) is applicable in many experimental situations, the model has several limitations if an experimenter wants to analyze and fit growth curves to the average growth of a population over time.
Article
Experimental studies with farmed juvenile halibut, Hippoglossus hippoglossus, were undertaken to optimize rearing procedures. Extended feeding period and/or day length did not significantly increase growth rates of juvenile halibut of 5 to 20 g wet weight. Growth was strongly affected by temperature, and highest growth rates were obtained at 13°C followed by 10, 16 and 7°C for juveniles of 20 to 90 g. Growth rate declined with size in one of two experiments in this size interval. Q10 of daily growth rate between 7 and 10°C varied from 2.5 to 3.0. Individual growth always varied highly within the temperature treatments (overall range −0.3 – 3.5%·d−1), but significant size rank correlations were maintained during the 12-week experiment. Juvenile halibut grew approximately isometrically from 20 to 90 g. Weight-specific oxygen consumptions of 80 g juveniles averaged 140 and 200 mg O2 (kg·h)−1 at 10 and 16°C, respectively, and this is comparable to rates measured for other flatfish species.
The time courses of extracellular ionic and acid-base adjustments were studied in juvenile turbot (Scophthalmus maximus) following a decrease of water salinity, either abruptly from 32 to 10%. or after a first step (4 weeks) in 19%. salinity followed by a direct transfer to 10%. brackish water (BW). Net exchanges of acid-base equivalents with the external water were also determined after transfer from 32%. SW to 10%. BW. Direct transfer from seawater (SW) to 10%. BW induced a transient decrease in plasma osmolarity, plasma sodium and chloride concentrations, associated with a marked and transient metabolic alkalosis in the blood. A significant net outflux of acidic equivalents was also measured only during the first day in BW. Four weeks preadaptation in 19%. BW reduced the intensity of the osmotic disturbances elicited by a subsequent abrupt transfer to 10%. BW. These ionic readjustments were also coupled with minimal acid-base changes, of lesser magnitude than those described after directly from SW to 10%. BW.
Article
The growth and growth dynamics of juvenile Atlantic salmon (Salmo salar) exposed from mid-August to mid-December to either a normal light:dark cycle (LDN) or a constant 16-h light:8-h dark (LD 16:8) photoperiod were compared. Exposure to the LD 16:8 resulted in 38.1% of the fish entering the upper modal group (UMG) of the length–frequency distribution, while only 15.4% entered the UMG under LDN. The length at which fish entered the UMG (critical fork length) did not differ between photoperiods. Fish in the small (5.8–6.7 cm) and middle (6.8–7.7 cm) size-ranges under LD 16:8 had greater growth rates than fish in the same size-ranges under LDN. Fish in the large (8.3–9.2 cm) size-range showed no significant variation in growth rates between photoperiods. At the end of the experiment, mean thyroxine (T4) levels were significantly (P < 0.05) lower in fish from the LD 16:8 photoperiod (1.69 ng/mL) in comparison with LDN fish (3.96 ng/mL). Triiodothyronine (T3) levels and the T3/T4 ratio were elevated under LD 16:8.
Article
The effect of dietary water content and feeding rate on the growth and food conversion efficiency of turbot was investigated using diets which contained identical amounts of dry nutrient material but different quantities of water, ranging from 0 to 74%. The dietary water content did not significantly influence the growth, composition, condition factor or food conversion efficiency of the turbot. It appeared that, as long as the basic nutrients were formulated so as to produce an adequate diet, the water content was immaterial. The over-riding factor governing growth was the rate of food intake. Comparisons at feeding rates which in energy equivalents ranged from 24 to 72 calories per gram of fish a day, showed that the higher the energy intake the more rapid the growth. At the highest feeding rate, fast growth was accompanied by a marked increase in the condition factor and an elevated lipid content of the fish. The percentage protein content, however, was relatively stable in relation to the feeding rate. Food conversion efficiency was also relatively stable. On average, 40.3% of the dietary protein and 36.3% of the ingested energy was converted into turbot.
Article
Arctic charr, Salvelinus alpinus, were reared in either unsorted groups or in groups that had been sorted into ‘small’ and ‘large’ fish. At the start of the experiment the size-frequency distributions of unsorted and pooled ‘small’ and ‘large’ fish were similar, but after 5 months' rearing distributions were markedly different. There was evidence that growth of ‘small’ fish improved in the absence of larger conspecifics, but size-sorting also led to reduced growth of some large fish, with the consequence that size-sorting did not lead to overall increases in biomass gain and rates of production.
Article
Abstract Feed intake and growth were studied in groups of turbot fed daily rations of 0.25%, 0.38% and 1% of body weight day–1 for 41 days. Then, all groups were fed 1% of body weight day–1 for the next 34 days. The two restricted rations resulted in reduced growth rates (30% and 60% of fully fed controls), and there was a tendency for increased growth heterogeneity (coefficient of variation increased from about 100% to about 150%) compared with controls on full rations. Nevertheless, restricted rations did not result in any increase in size heterogeneity with the passage of time: the coefficient of variation for weight changed little irrespective of feeding treatment. The turbot became hyperphagic and displayed compensatory growth after the change from restricted to excess feeding, with compensatory growth being most marked among the fish that had been subject to the most severe feed restriction. The results provided some evidence of increased variability in feeding and growth within groups of turbot fed restricted rations, possibly as a result of the establishment of weak feeding hierarchies. When feeding restrictions were lifted, the turbot that had reduced growth under feed restriction were able to completely compensate for lost growth.
Article
Routine oxygen consumption of turbot, Scophthalmus maximus, was determined in relation to temperature, salinity, body wet weight, and time of day. The highest routine oxygen consumption rates measured roughly followed a arabolic curve over the temperature range tested (8 to 24°C). The lowest rates showed a more linear refationship over the same temperature range. It is argued that lowest rates correspond to the standard oxygen consumption. Between 16 and 19°C, routine oxygen consumption reached a maximum. It is suggested that these temperatures correspond to the preferred ternerature of the species and are within the range of optimum temperature for growth of specimens weigkng about 100 g. Salinity effect on oxygen consumption rates was studied in five groups acclimated over 4 weeks to 8, 15, 22, 29, and 35%. salinity. Routine oxygen consumption rates were lowest at 8% salinity with no significant differences in higher acclimation salinities. Routine respiration of turbots showed conspicuous daily fluctuations. During spring, summer, and autumn, oxygen Consumption was higher during morning hours and at night. In winter, higher rates were measured only once (during morning and early afternoon). The relationship between routine oxygen consumption and body weight of turbots followed an exponential function with a slope of 0.7, which was lower compared to the slope of 0.8 usually given for roundfish-species.
Article
Causes of size variation in a population of juvenile turbot were studied using an individual based model (IBM). Each simulation started with 800 (divided into eight groups of 100 each) 120-day-old (posthatch) juveniles and was run for 140 days, and the data gained from model simulations compared directly with the result of a laboratory study with size-graded turbot. Stochastic growth with memory, which was included in the models as an individual genetical growth rate variation, is important in explaining size variation, and the combination between individual genetic growth rate and social interactions related to size-dependent hierarchies also contributes to size variation. The use of size-dependent growth rate alone fails to explain size variation, and is of little value in predicting size variation in turbot culture. Further, the results indicate formation of different types of size hierarchies for different sizes of juvenile turbot.
Article
The development of a recombinant turbot somatotropin (rtuGH) in Escherichia coli and an homologous antibody in rabbit has produced a sensitive and specific RIA allowing the measurement of blood levels and pituitary contents of tuGH and their responses to environmental change. Turbot IGF-1 (insulin growth factors) and IGF type 1 receptor (R) cDNA have also been cloned and sequenced. The deduced IGF-1 R primary sequence contains all the topological features characteristics of mammalian IGF-1 R and the turbot R appears highly conserved, compared to its mammalian counterpart, particularly within the catalytic domain. IGF-1 R mRNA polyadenylation status varies during development with polyadenylation occuring in oocytes and early stage larvae. It disappears in later stages and in adult somatic tissues, indicating that IGF-1 R mRNA undergoes complex post-transcriptional regulation. Thyroid hormones (TH, both T3 and T4), are also involved in growth control, but are less affected by environmental changes than GH, except in very extreme conditions. The thyroid stimulating hormone (TSH) β-subunit cDNA fragment has also been cloned and sequenced. mRNA expression levels have been quantified under conditions where blood circulating TH were modified by dietary treatments or hormone supplementation. Specific growth rate in turbot is related to food intake and is doubled with a temperature increase from 8 to 20° C. Lipid storage by contrast was higher at low temperatures. Over a long time course, growth rate in turbot can be improved in brackish water (8–20 psu) but it cannot adapt to very low salinities. Photoperiod appears to have little influence on growth when feeding is unrestricted. Under intensive farming conditions, ammonia, the major nitrogen waste product in teleosts, may increase to levels that can reduce growth. Safe ambient levels for growth are <2–3 mg l−1 TAN above which a 10–20% decrease in growth was recorded within 3 months. Over 20 mg l−1, feeding stops and no growth occurs. Turbot juveniles can cope efficiently with relatively large fluctuations in ambient oxygen, but major disruptions to physiological functions occur below 20% of air saturation. Under moderate hypoxia growth is reduced by 20% within 1.5 months. The primary response to hypoxia or ammonia accumulation is always a decrease of food intake.
Article
Compensatory growth responses of rainbow trout Oncorhynchus mykiss were studied by examining food intake and growth of individual fish held within groups that were switched between regimes that involved full and restricted feeding. Restricted feeding led to marked interindividual variability in food intake, probably as a result of the establishment of feeding hierarchies. This disparity in food acquisition was reflected in highly heterogeneous growth amongst the fish fed low rations. When fish were transferred from restricted to full rations, they became hyperphagic and displayed high rates of growth. Growth compensation was most marked amongst those fish which had shown the poorest growth during the period of feed restriction. These results suggest that the feeding hierarchies established under feed restriction did not persist, but were rapidly broken down when food became increasingly available, enabling the previously suppressed fish to gain access to food and to display rapid growth.
Article
The effects of salinity changes (27, 19 and 10‰) on seawater-adapted juvenile turbot were studied on their plasma osmolarity and ion concentrations, on oxygen consumption, on gill Na+,K+-ATPase activity after 3 months and on growth parameters. All plasma concentrations (except chloride) were unchanged, suggesting that fish were well adapted to their environment. Oxygen consumption was significantly decreased in the 19 and 10‰ groups, where fish weighed significantly more 105 days after transfer than fish maintained in sea water. These results, and the fact that apparent food conversion rates were lower in a diluted environment, suggest that on a long term schedule growth conditions could be improved by adaptation to brackish waters (salinities between 10 and 19‰). The effects of transfer from sea water to 27, 19, 10 and 5‰ were also followed during the first 3 weeks. With salinity 10‰ a steady state was reached on day 21 with all plasma values within the same range. The significant differences observed in osmolarity, plasma ion concentrations and Na+,K+-ATPase activity 3 weeks after transfer of juveniles to 5‰ salinity, compared with transfers in higher salinities, suggest that there is a threshold of acclimation of turbot to a hypotonic environment.
Article
Growth rate of individually tagged medium–sized (249±6·9 g) juvenile halibut was 18% lower when medium sized fish were reared alone (treatment Mm) as compared with rearing with either large/dominant (382±12·1 g) (Ml) or small/subordinate (158±3·1 g) (Ms) conspecifics. The coefficient of variation of weight of medium–sized fish increased with weight in both the Mm and the Ml group whereas it was stable in the Ms group. Size rank correlation between initial and final weight was highest in the Mm group and lowest in Ms. A negative rank correlation was found also between initial weight and overall growth rate for the Ms treatment groups but not the other groups. It is hypothesized that interactions between similar–sized individuals in the Mm treatment group had an inhibiting effect on growth as social hierarchies were being resolved.
Article
During their first 6 months sibling Atlantic salmon parr, Salmo salar L., grew larger under constant light than under natural photoperiod or simulated natural photoperiod (control). When rate of change of photoperiod was accelerated after midsummer, ×2, ×3 and ×4, there were no growth differences between the three groups, but all were smaller than the control population. Under constant autumn photoperiod of 8 h light: 16 h dark growth was less than under all other experimental photoperiod conditions. Mean length was directly correlated with total hours of daylight experienced, excluding those fish kept under constant light.
Article
Juvenile cichlids, Tilapia zillii, of equal initial standard length were randomly assigned to one of five treatments to assess the relative importance of individual physiological and activity differences, disproportional food consumption, and social interaction on growth depensation and mean growth. Results substantiate the hypothesis that disproportional food acquisition is the primary mechanism responsible for the size hierarchy effect. Individual physiological and activity differences played a negligible role in the phenomenon. Dominant-subordinate relationships, set up in the aquarium, appear responsible for the disproportional food acquisition and thus mediate the size hierarchy effect. Dominant fish ingest more food by either acquiring a limited ration first, preventing a subordinate''s food acquisition, or behaviorally inhibiting a subordinate''s feeding behavior.
Article
Juvenile Atlantic salmon were reared under simulated natural photoperiod (LDN) from first feeding in May until late August. Three 16-h daylength regimes were started in August or September and continued until November or December (LD16:8 A-N; LD16:8 S-N; LD16:8 S-D). A control group remained on LDN. The fish reared under LD16:8 regimes became significantly larger soon after the start of photoperiod manipulation; these differences increased during autumn and persisted until completion of smolting in May. The LD16:8 A-N regime had a significantly higher proportion of fish in the upper-modal group than all other treatment groups. Based on length > 13.5 cm, all LD16:8 regimes produced significantly more smolt-sized fish than LDN. Thyroid hormone (T3, T4) levels rose in October-November in all treatment groups and declined in December-January. T3 and T4 levels rose slightly in February. T4, but not T3, continued to rise in March. Pituitary somatotrop and thyrotrop activity (mitotic figures and granulation) was observed in all groups in September-October, with most activity in LD16:8 groups. There was within-group variation in somatotrop activity, possibly in relation to faster and slower growing fish. All groups had transitory, high levels of salinity tolerance in early December. Although gill Na+K+-ATPase activity and salinity tolerance rose earlier and to a greater extent in LDN than in LD16:8 treatments, all groups appeared to reach smolt status in May as judged by high survival and growth rates during 6 months in seawater. The LD16:8 S-D group appeared to complete smolting later than the LD16:8 A-N and S-N groups and LDN. Thus, the application of LD16:8 daily light cycles to salmon during their first autumn increases the proportion of fish in the uppermodal group (presumptive smolts) and has only minor effects on the timing of completion of smolting the following spring.
Article
Juvenile turbot were fed diets containing various proportions of protein and lipid. The fastest growth occurred on a diet rich in protein and low in lipid. The addition of extra lipid to the diet gave poorer growth but improved protein conversion efficiency. The protein sparing action of the lipid was most pronounced when the turbot were fed to about three-quarters of satiation on a diet supplemented with 6% lipid. Under these conditions 42% of the dietary protein was converted into fish protein, compared with 32% conversion on the basic diet which contained 0.5% lipid. There was a general decline in food conversion efficiency and protein sparing was marginal at the satiation feeding rate. Not all the dietary lipid was used in a protein sparing role, much of it was deposited as lipid reserves. In contrast, there was very little increase in the lipid content of fish fed on a high protein-low lipid diet.
Article
Physiological studies of growth in animals predict that growth rates should decrease with increasing size, but when Arctic charr, Salvelinus alpinus, were reared together in large groups there was often a positive correlation between initial body size and the growth rate of an individual fish. This suggested that social interactions were important determinants of growth rates and, in the absence of the establishment of direct linear hierarchies, it is suggested that growth suppression is the result of short-term bouts of aggression associated with feeding periods leading to reduced food intake by certain fish. Evidence is presented to show that growth suppression can be reduced by increasing the frequency of feeding.
Article
Groups of Atlantic salmon (Salmo salar L.) postsmolts were reared in sea cages under natural light or continuous additional light from 20 February to 24 June. The two light regimes were combined with two feeding regimes in a 2 by 2 factorial design. No significant differences in growth rate were found between the feeding regimes. Growth rate and incidence of grilsing were highest in the groups subjected to continuous additional light.
Article
Juvenile turbot (5–125 g) were reared under two experimental temperatures: 10°C and 16°C, and three experimental photoperiods: LDN (natural photoperiod), LD 16:8 (16 h light: 8 h darkness), LD24:0 (continuous light), to study effects of temperature and photoperiod on growth, activity and oxygen consumption. Growth was strongly affected by temperature and was higher at 16°C than at 10°C. Continuous light had a growth-promoting effect at 10°C from mid-December to late March, while at 16°C this effect was restricted to December and January. A seasonal change in the condition index was found. The groups reared in continuous light had higher condition indices in winter. The experimental groups held at 16°C had higher O2 consumption than those at 10°C. The LD24:0 groups invariably had a higher overall O2 consumption than did the LDN and LD16:8 groups, the differences being caused by reduced O2 consumption in the latter groups during darkness. The LD24:0 groups displayed higher activity than the LDN groups, in which activity was very low at night.
Article
The effects of photoperiod on growth of juvenile turbot and the consequences of extended daylength on age at first maturation were investigated. Growth of individually tagged turbot (initial weight 34–44 g, n = 94) was monitored for 18 months. The fish were held under natural photoperiod from hatching (July) until the start of the experiment in December. From December 4, 1991 until May 26, 1992, the fish were reared under constant light (LD24:0, n = 27), 16-h light:8-h darkness (LD16:8, n = 35), or simulated natural photoperiod for 60 °25′N (LDN, n = 32). The fish were then reared together on LDN for 12 months until first maturation during summer 1993 (age 24 months). The fish were held at 16 °C from December 1991 onwards. A growth promoting effect of extended daylength was seen in the LD16:8 and LD24:0 groups, but the effect was not apparent in the LD24:0 group until 6 months after the fish had been transferred to LDN. The final mean weights of the female turbot were 1727 g and 1777 g in the LD16:8 and LD24:0 groups, respectively, whereas final mean weights of males in these groups were 1075 g and 1055 g. In the LDN group the final mean weights for females and males were 1290 g and 909 g, respectively. The results from the present study suggest that exposure to extended photoperiod alters the growth pattern of both maturing fish and immature fish resulting in increased overall growth. Fewer males matured in the LD16:8 (26%) and LD24:0 (17%) groups than in the LDN (56%) group, whereas there were no differences between the experimental groups in the proportion of females that matured (range = 60–63%). It is concluded that extended daylength
Article
The most important physiological and endocrinological changes occurring in rainbow trout subjected to common forms of aquacultural stress are described. It is demonstrated that plasma cortisol elevation, as a direct result of stress-induced activation of the hypothalamic-pituitary-interrenal axis, is a major factor responsible for the damaging effects of stress on survival, growth and reproduction. In the light of this knowledge, a series of practical guidelines is developed to enable fish farmers to minimize such damage. Future lines of research, to accelerate the rate of domestication of rainbow trout by means of selectively breeding fish with a reduced stress response, are discussed.
Article
The stress response in teleost fish shows many similarities to that of the terrestrial vertebrates. These concern the principal messengers of the brain-sympathetic-chromaffin cell axis (equivalent of the brain-sympathetic-adrenal medulla axis) and the brain-pituitary-interrenal axis (equivalent of the brain-pituitary-adrenal axis), as well as their functions, involving stimulation of oxygen uptake and transfer, mobilization of energy substrates, reallocation of energy away from growth and reproduction, and mainly suppressive effects on immune functions. There is also growing evidence for intensive interaction between the neuroendocrine system and the immune system in fish. Conspicuous differences, however, are present, and these are primarily related to the aquatic environment of fishes. For example, stressors increase the permeability of the surface epithelia, including the gills, to water and ions, and thus induce systemic hydromineral disturbances. High circulating catecholamine levels as well as structural damage to the gills and perhaps the skin are prime causal factors. This is associated with increased cellular turnover in these organs. In fish, cortisol combines glucocorticoid and mineralocorticoid actions, with the latter being essential for the restoration of hydromineral homeostasis, in concert with hormones such as prolactin (in freshwater) and growth hormone (in seawater). Toxic stressors are part of the stress literature in fish more so than in mammals. This is mainly related to the fact that fish are exposed to aquatic pollutants via the extensive and delicate respiratory surface of the gills and, in seawater, also via drinking. The high bioavailability of many chemicals in water is an additional factor. Together with the variety of highly sensitive perceptive mechanisms in the integument, this may explain why so many pollutants evoke an integrated stress response in fish in addition to their toxic effects at the cell and tissue levels. Exposure to chemicals may also directly compromise the stress response by interfering with specific neuroendocrine control mechanisms. Because hydromineral disturbance is inherent to stress in fish, external factors such as water pH, mineral composition, and ionic calcium levels have a significant impact on stressor intensity. Although the species studied comprise a small and nonrepresentative sample of the almost 20,000 known teleost species, there are many indications that the stress response is variable and flexible in fish, in line with the great diversity of adaptations that enable these animals to live in a large variety of aquatic habitats.
Does light have an influ-ence on fish growth? Aquaculture 177, Control of the somatic growth in turbot Environmental factors and growth Effect of dietary protein, lipid and energy content on the growth of turbot (Scophthalmus maximus L.)
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A preliminary study of comparative growth rates in O-group malpigmented and normally pigmented turbot, Scophthalmus maximus (L.), and turbot-brill hybrids
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