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Short-term Effects of First-prey Type and Number on Survival and Growth of Intensively Cultured Spotted Seatrout, Cynoscion nebulosus (Sciaenidae), Larvae
Journal of the World Aquaculture Society
Abstract
Five test diets – 20, 10 rotifers/mL/d, 5 rotifers/mL/d + 3 nauplii/mL/d, 5 and 8 nauplii/mL/d – were used to examine the effect of Acartia tonsa nauplii and a small strain of rotifers on survival, myotome height, notochord length, and condition (myotome height/notochord length) of spotted seatrout, Cynoscion nebulosus, larvae through 6-d posthatch (PH). Diet did not affect survival. Larvae fed 5 and 8 nauplii/mL or 5 rotifers + 3 nauplii were longer, taller, and in better condition than larvae fed either 10 or 20 rotifers/mL. The condition of larvae fed diets with nauplii declined after Day 5 which suggests a shortage of prey in those diets after Day 4 or 5. Although copepod nauplii offer substantial short-term benefits in the culture of spotted seatrout, further study is required to determine the number of nauplii and/or rotifers necessary in the diet beyond Day 4 and to assess the long-term impact of the different diets.
... Nauplii of calanoid copepods, which are considered superior to rotifers and brine shrimp, were offered during early feeding (through day 6) of seatrout larvae by Lemus, Blaylock, Apeitos, and Lotz (2010). The inclusion of copepod nauplii did not increase survival, but larvae fed either copepods alone or in combination with rotifers were larger and in better condition than those fed rotifers alone, perhaps because copepods provided a nutritional supplement. ...
... Larvae fed copepods also tended to be more uniform in size than those fed rotifers. Despite the positive effects of copepods on early growth, Lemus et al. (2010) concluded that the benefits of copepods are currently outweighed by the cost and difficulty in providing a sufficient number of copepod nauplii to support largescale culture. ...
Culture models and facilities for large-scale, commercial production of popular Gulf of Mexico species are unavailable. The spotted seatrout (Cynoscion nebulosus) is one of the most popular recreational fishes in the Gulf of Mexico. Seatrout culture techniques were adapted from red drum (Sciaenops ocellatus) protocols developed in the 1970s. Broodstock husbandry, spawning, and extensive pond rearing techniques using fertilized and bloomed brackish ponds were well-established by the 1980s. By 2018, approximately 80 million 25–30-day old seatrout had been produced, mainly for stock enhancement. Cannibalism and poor nutrition hindered intensive tank culture. Between 2005 and 2015, an intensive tank-rearing protocol that reduced cannibalism and intracohort variability and increased average survival to almost 50% was developed using algal concentrate, rotifers, brine shrimp (Artemia sp.), and microencapsulated feeds. Preliminary results suggested that a 500 g fish could be produced in approximately 10 months. Nevertheless, interest in commercialization has remained low. Zootechnical performance throughout the latter stages of culture, the economics of production, consumer preferences/perceptions, and market capacity must be documented to complete the assessment of the spotted seatrout as a species for commercial aquaculture. The optimization of aquafeeds specific for seatrout and a domestication program is warranted to further facilitate industry growth.
... Chaetognatha is rarely a dominant prey item in larval fish diets but has been reported in Scombridae from Northwest Australia (Sampey et al., 2007), which are known for their voracious piscivory during their larval stages (Shoji and Tanaka, 2001;Uriarte et al., 2017). Here, we propose that the consumption of Chaetognatha in C. nothus may be linked to an early onset of piscivory, which is known for its sister species C. nebulosus (Lemus et al., 2010;Manley et al., 2014;Manley et al., 2015) and supported by our finding of a fish in the gut of one C. nothus at PFlex.2. Targeting Chaetognaths that exhibit a similar swimming behavior and undulation pattern as some fish larvae (Batty, 1984;Jordan, 1992;Vlymen, 1974) may help C. nothus to transition to piscivory once their morphology (gape width, swimming speed) allows. ...
The ability of larval fish to find prey items in sufficient quantities plays an important role in determining survivorship. To understand trophic niche partitioning and the potential for competition, we analyzed morphology and digestive tract content in larvae of three co-occurring, sciaenid fish species: Cynoscion nothus, Larimus fasciatus and Micropogonias undulatus. Larvae were collected in the north-western Gulf of Mexico off Galveston, TX, at seven stations in October/November 2017. Intra- and interspecific diet composition was analyzed between three ontogenetic development stages and two sampling zones (nearshore vs mid-shelf). M. undulatus had a significantly smaller mouth size than the other two species and consumed smaller prey items compared with C. nothus. Copepoda dominated all larval diets. The highly abundant M. undulatus primarily ate Calanoida following typical Sciaenidae feeding preferences. The less abundant C. nothus and L. fasciatus shared Cyclopoida as a primary diet item but differed in the consumption of less important prey taxa (i.e. Ostracoda, Chaetognatha). Ontogenetic dietary shifts (ODSs) were observed for all species, with the timing and number of ODS differing for C. nothus between sampling zones. The inclusion of alternative food sources such as Cyclopoida and non-copepod prey taxa likely alleviated potential interspecific competition allowing for larval co-occurrence.
... Although these live feeds have proven successful with numerous fish species currently grown, their acceptance by many desirable marine fish species has provided insufficient survival (Hamre, Srivastava, Ronnestad, Mangor-Jensen & Stoss 2008). The successful utilization of copepods as live prey for marine fish larvae is well documented (Evjemo, Reitan & Olsen 2003;Hernandez Molejon & Alvarez-Lajonchere 2003;Lee, O'Bryen & Marcus 2005;Olivotto, Holt, Carnevalli & Holt 2006;Wilcox, Tracy & Marcus 2006;Lemus, Blaylock, Apeitos & Lotz 2010;Cassiano, Ohs, Weirich, Breen & Rhyne 2011;Leu, Meng, Siong, Kuo & Hung 2012). Using copepods not only improves growth, survival and other characteristics in species currently grown using traditional live feeds (i.e. ...
Feeding copepods during early larval culture stages of marine fish has proven to be advantageous for growth and survival of marine finfish larvae. However, commercial availability of most copepods is limited; thus, there is an impetus to evaluate promising copepod species to meet the diverse dietary demands of various marine fish. The marine cyclopoid copepod, Oithona colcarva, was isolated out of zooplankton samples taken from waters within Tampa Bay, Florida. Once isolated, trials were conducted to determine the appropriate culture parameters for producing nauplii to feed marine fish larvae. The effects of temperature (22°C, 26°C and 30°C), salinity (15, 20, 25, 30 and 35 g L−1), stocking density (0.5, 1.0, 2.0, 4.0 and 8.0 individuals mL−1) and diet (Nanno 3600 microalgae paste, Colurella adriatica, Rhodomonas lens, Tisochrysis lutea, Chaetoceros gracilis and/or Tetraselmis chuii) on nauplii production during a single life cycle of reproducing individuals were examined. Results of those trials indicated that a culture temperature of 30°C and a salinity of 30 g L−1 were advantageous for maximum nauplii production. Furthermore, a diet containing a 1:1:1 mixture of T. lutea, C. gracilis and T. chuii and a stocking density of at least 8 individuals mL−1 were identified as beneficial. The results of these trials, the potential for large-scale culture and observations on the performance of marine fish larvae fed Oithona colcarva nauplii are discussed.
... También se ha demostrado que el uso de análogos de la hormona liberadora de gonadotropina (LHRHa), administrada por vía oral en dosis de 1 mg kg -1 de pez, induce efectivamente al desove (Thomas & Boyd 1989), así como también se han obtenido desoves naturales con control de temperatura y fotoperiodo (Wisner et al. 1996). Por otro lado, la cría de larvas de esta especie ha recibido gran atención y ha sido estudiada con enfoques fisiológicos (Banks et al. 1991), metabólicos (Wuenschel & Werner 2004, Wuenschel et al. 2004, alimentarios, como la determinación de la densidad del alimento óptima en los primeros días del cultivo larvario (Lemus et al. 2010) y el efecto de la densidad sobre el comportamiento agresivo (canibalismo) (Manley et al. 2014). ...
The first experiments in maturation, spawning and larval rearing of spotted seatrout Cynoscion nebulosus in Sisal, Mexico were conducted. Sexual maturation and spontaneous spawning in wild captured fish after 20 months in captivity were obtained. In a spawning period of 88 days, 28 spawns were observed, of which 17 were viable. In total 28 x 10(6) eggs were collected, 70% of viability and 91% of fertilization was observed. The spawned eggs had mean diameter of 710 ± 8 µm with an oil droplet of 199 ± 9 µm. The percentage hatching of viable eggs was 96% and larval survival at 48 h after hatching was 79%. At 48 h post-hatch (PH), no traces of yolk and only traces of the oil droplet were observed. The most appropriate period for first feeding period is between 30 and 42 h PH, after which the mean survival decreases sharply to 9.3 ± 4.4% and 11.3 ± 4.8% at 54 h PH and 66 h PH, respectively. The larval rearing was done in 2 tanks, 4-m³ with an initial density of 75 viable eggs L-1 (95.6% fertilization, hatching 97.7% and 88.8% survival at 48 h). Survivals were 0.4 and 1.2% at 26 days, with 1011 and 2903 juveniles harvested, with wet weights of 0.13 ± 0.04 g and 0.16 ± 0.03 g and total lengths of 25.3 ± 2.6 mm and 27.4 ± 1.9 mm respectively. Final densities and biomasses were 0.25 and 0.50 juveniles L-1 and 0.03 and 0.08 kg m-3, respectively.
... También se ha demostrado que el uso de análogos de la hormona liberadora de gonadotropina (LHRHa), administrada por vía oral en dosis de 1 mg kg -1 de pez, induce efectivamente al desove (Thomas & Boyd 1989), así como también se han obtenido desoves naturales con control de temperatura y fotoperiodo (Wisner et al. 1996). Por otro lado, la cría de larvas de esta especie ha recibido gran atención y ha sido estudiada con enfoques fisiológicos (Banks et al. 1991), metabólicos (Wuenschel & Werner 2004, Wuenschel et al. 2004, alimentarios, como la determinación de la densidad del alimento óptima en los primeros días del cultivo larvario (Lemus et al. 2010) y el efecto de la densidad sobre el comportamiento agresivo (canibalismo) (Manley et al. 2014). ...
The first experiments in maturation, spawning and larval rearing of spotted seatrout Cynoscion nebulosus in Sisal, Mexico were conducted. Sexual maturation and spontaneous spawning in wild captured fish after 20 months in captivity were obtained. In a spawning period of 88 days, 28 spawns were observed, of which 17 were viable. In total 28 × 106 eggs were collected, 70% of viability and 91% of fertilization was observed. The spawned eggs had mean diameter of 710 ± 8 μm with an oil droplet of 199 ± 9 μm. The percentage hatching of viable eggs was 96% and larval survival at 48 h after hatching was 79%. At 48 h post-hatch (PH), no traces of yolk and only traces of the oil droplet were observed. The most appropriate period for first feeding period is between 30 and 42 h PH, after which the mean survival decreases sharply to 9.3 ± 4.4% and 11.3 ± 4.8% at 54 h PH and 66 h PH, respectively. The larval rearing was done in 2 tanks, 4-m3 with an initial density of 75 viable eggs L-1(95.6% fertilization, hatching 97.7% and 88.8% survival at 48 h). Survivals were 0.4 and 1.2% at 26 days, with 1011 and 2903 juveniles harvested, with wet weights of 0.13 ± 0.04 g and 0.16 ± 0.03 g and total lengths of 25.3 ± 2.6 mm and 27.4 ± 1.9 mm respectively. Final densities and biomasses were 0.25 and 0.50 juveniles L-1 and 0.03 and 0.08 kg m-3, respectively.
The availability of Spotted Seatrout Cynoscion nebulosus to anglers along the Texas coast is supported by a stock enhancement program that is managed by the Texas Parks and Wildlife Department. A study was conducted to improve production protocols during frequent hypersaline conditions in rearing ponds. The objectives of the study were to (1) develop a feeding protocol for use during extended indoor larval rearing and (2) determine whether gradual hypersaline acclimation during extended indoor larval rearing leads to increased growth and survival of Spotted Seatrout larvae when they are subjected to hypersaline conditions. Two feeding trials were conducted to evaluate four rotifer enrichments (Algamac‐3050, Easy Dry Selco, Ori‐One, and Rotigrow Plus) that are used in a standard larval Spotted Seatrout diet. The feeding trials were necessary to ensure larvae health and survival for the salinity acclimation trial. The larvae in both trials that were fed with Algamac‐3050‐enriched rotifers exhibited significantly greater (P < 0.05) survival and growth (i.e., length, weight, specific growth rate, and percent weight gain). Based on these results, Algamac‐3050 was used in a subsequent salinity acclimation trial. In the salinity acclimation trial, 3‐d‐posthatch (dph) larvae at 35‰ were subjected to increased salinity at a rate of 1‰/d; then at 3, 6, 9, and 12 dph, they were subjected to a hypersaline (50‰) condition to simulate pond stocking. The percentage of survival was highest when the larvae were acclimated until 6 or 9 dph (52.5 ± 7.0% and 65.0 ± 7.7% [mean ± SD], respectively) with no improvement in acclimation to 12 dph (65.2 ± 7.1%). The results for growth and percentage survival displayed similar trends. This study indicates that rearing larval Spotted Seatrout in hypersaline conditions is improved by increasing the indoor rearing time beyond 3 dph and gradually acclimating the larvae to a higher salinity during an extended rearing time.
Th e us e o f liv e pre y i s stil l necessar y fo r a larg e numbe r o f raise d fi s h species . Smal l size d rotifer s ar e usuall y use d a s liv e prey s durin g th e ¢rs t day s o f feedin g i n smal l mout h fi sh . A n alternativ e t o thi s i s th e us e o f copepod s a s pre y fo r ¢rs t feeding . I n thi s study , th e sizes , weigh t an d biochemica l content s o f tw o copepod s an d on e rotife r specie s raise d o n simila r alga l foo d condition s wer e compared . Rotifer s containe d a highe r proportio n o f essentia l amin o acid s i n th e fre e amin o aci d (FAA ) fractio n (43% ) tha n copepod s (30-32%) . However , rotifer s ha d lowe r level s o f importan t fatt y acid s lik e DH A (7 % compare d wit h 23-32 % i n copepods ) an d thei r DHA/EP A rati o wa s lowe r tha n tha t i n copepod s (0.54 compare d wit h 1.35-1.6 3 i n copepods) . Th e FA A patter n o f th e prey s tende d t o b e species-speci¢ c an d it s implication s fro m a n aquacultur e poin t o f vie w i s discussed . I n contrast , the-protei n boun d amin o acid s tende d t o b e ver y conservativ e amon g th e studie d organisms . Th e secon d par t o f th e wor k i s focuse d o n 'th e price ' o f hatchin g i n Acarti a tons a egg s befor e o r afte r col d storag e a t 3 1 C . Th e fatt y aci d content s i n A . tons a tende d t o decreas e wit h th e storag e time . I t als o decrease d wit h hatchin g o f th e nauplii , bu t it s proportio n compare d wit h th e dr y weigh t remaine d constant . Vol. 37, issue 8, p756-772
The application of large marine enclosures for early life history studies has revealed important information for cultivation methods of fish larvae. During the 1970s and 1980s extensive and semiintensive methods were developed for cultivation of Atlantic cod, turbot, Atlantic halibut, seabass, and sea bream. In Norway, the lagoon enclosure technique was the predominant method in the late 1980s. The extensive method, applied mostly for cod, is defined as larval rearing in lagoons or ponds, where larval feeding is based entirely on natural plankton production in the system. In contrast, the semiintensive method is defined as larval rearing in large tanks or plastic bags, where food organisms are collected and concentrated from extensive lagoon or pond systems before being feel to the fish larvae. Copepods are the predominant food item produced with these techniques, but variability of copepod productivity in relation to the food demands of the larval population has been a major problem. At present in Norway only halibut juveniles are commercially reared using such systems. In Denmark, extensive rearing techniques for turbot in concrete tanks were developed in the early 1980s and are still commercially applied in a more semiintensive manner. This article reviews the development of the extensive and semiintensive rearing methods for marine fish larvae and gives a short outline of the different adaptations of the methods. Commercialization of the methods is discussed in relation to their constraints.
A 28-day feeding trial was conducted for comparing the effect of different dietary phospholipid (PL) classes on the growth of post-larval turbot and on the incorporation of dietary neutral lipid fatty acids into their body lipids. Prior to the experiment the turbot were weaned for one week on a PL-free diet. The nine experimental diets were isolipidic and contained an equal amount of highly unsaturated fatty acids in the form of ethyl esters. They differed by their PL content (0, 1 or 2%) and by the PL class composition of the added soybean PL fractions.
Compared to the PL-free diet, diets enriched with phosphatidylcholine (PC) resulted in a better growth, a higher triglyceride content (% body dry matter) and increased levels of docosahexaenoic acid (% total fatty acids) in each of the examined body lipid classes (neutral lipid, phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol). The effects of the other soybean PL fractions were less explicit than those noted for soybean PC.
The results support the idea that dietary PC plays a role in the intestinal absorption of neutral lipid fatty acids. This might, at least partially, explain the superiority of PC for enhancing growth. Abbreviations: DHA – docosahexaenoic acid (22:6n-3); EPA – eicosapentaenoic acid (20:5n-3); HUFA – highly unsaturated fatty acid; PA – phosphatidic acid; PC – phosphatidylcholine; PE – phosphatidylethanolamine; PI – phosphatidylinositol; PL – phospholipid; PS – phosphatidylserine; PUFA – polyunsaturated fatty acid.
Although global production of flatfish has increased in recent years, both in terms of numbers of fish and diversification into new species, problems still remain with low survival rates and difficulties with metamorphosis. This short review highlights some advances made in optimising lipid nutrition in an attempt to overcome some of these problems. Copepod nauplii are the best live prey for first-feeding flatfish larvae. Rotifers can provide a useful method of essential fatty acid delivery but Artemia are poorer in this regard, especially at first feeding. Copepods are nutritionally beneficial due to their naturally high levels of the essential highly unsaturated fatty acids (HUFA), 20:5n-3 (eicosapentaenoic acid; EPA) and 22:6n-3 (docosahexaenoic acid; DHA), which are predominantly in the form of phospholipids. Rotifers can be enriched with fish oil emulsions to provide compositions similar to copepods, while enriched Artemia are difficult to enrich with high levels of DHA and the HUFA tend to be located in triglycerides rather than phospholipids. There is considerable evidence that the superior efficacy of copepods and rotifers is largely due to the digestibility and availability of HUFA supplied as pre-formed phospholipids. In addition to the essentiality of EPA and DHA, the requirement for 20:4n-6 (arachidonic acid; ARA) should also be considered. Improvements in dorsal pigmentation in turbot and halibut can be achieved by providing ratios of DHA/EPA of >2:1 but, perhaps more importantly, an EPA/ARA ratio of >5:1. This suggests that eicosanoids are involved in the control of pigmentation and this is further supported by the use of enrichments containing 18:3n-6, the elongation product of which (20:3n-6), is a potent inhibitor of ARA-derived eicosanoid formation, as is EPA.
Research on the dietary requirements of marine fish larvae has evolved from considerations of optimal dietary levels of n−3 HUFA to considerations of optimal dietary ratios of the two principal HUFAs, 22:6n−3 and 20:5n−3, and more recently to considerations of optimal dietary levels and ratios of all three dietary essential fatty acids, 22:6n−3, 20:5n−3 and 20:4n−6. Our present understanding of the requirements and optimal dietary balance of 22:6n−3, 20:5n−3 and 20:4n−6 is reviewed. Limitations of enriching live feed are considered, particularly from the point of view of achieving an optimal balance between levels of phospholipids and triacylglycerols in enriched live feeds that generate an optimal blend of essential fatty acids and energy-yielding fatty acids. It is concluded that the ideal marine fish larval diet is one containing circa 10% of the dry weight as n−3 HUFA-rich, marine phospholipids with less than 5% triacylglycerols, as exemplified by the lipid compositions of marine fish egg yolk, marine fish larvae themselves and their natural zooplankton prey. Such diets provide 22:6n−3, 20:5n−3 and 20:4n−6 in the desired levels and ratios and simultaneously satisfy known requirements for phospholipids, inositol and choline. Approaches to developing marine fish larval diets more closely resembling this “gold standard” diet are considered.
Though artificial propagation of Asian seabass Lates calcarifer (Bloch) in captivity through induced breeding techniques is standardized under Indian conditions, larval and nursery rearing techniques including suitable nursery feeds have to be standardized to obtain better survival and growth. Feeding experiments in triplicate were conducted to evaluate the suitability of the marine copepod Acartia clausi as live prey for fourteen day-old seabass larvae (6.53 ± 0.06 mm; 8.58 ± 0.33 mg) and compared with the traditional live prey, rotifers and Artemia nauplii. While A. clausi and rotifers were mass produced using algae Isochrysis galbana, Chaetoceros affinis and Chlorella marina, Artemia nauplii were produced using cysts. Nutritional quality of cultured copepods was evaluated based on the proximate composition, amino acid and fatty acid composition, and compared with that of rotifers and Artemia nauplii. Proximate composition varied significantly (P < 0.05) among the different live feeds. A. clausi showed higher protein (63.12%) and lipid (16.65%) content than Artemia nauplii and rotifers. Total essential amino acids content was 2% lower in A. clausi compared to that in Artemia nauplii. Fatty acid profiles of the live feed organisms showed that A. clausi is a rich source of n − 3 fatty acids. The total n − 3 fatty acid content of A. clausi was 33.94%. Length, weight overall weight gain and survivorship were significantly (P < 0.05) different among the dietary treatments, and weight gain was comparatively higher in A. clausi fed larvae. Survival of seabass larvae fed A. clausi was obtained highest as 58.13% against the lower values of 39.93% and 41.62% in larvae fed rotifer and Artemia nauplii respectively. Final carcass composition of the larvae of L. calcarifer fed different live-food organisms showed significant differences (P < 0.05) among the dietary treatments. The fatty acid composition of the dietary treatments was reflected to a certain extent in the fatty acid composition of the seabass larvae. The present investigation revealed the nutritional value of calanoid copepod and thus underlining its usefulness as a suitable live-food organism for rearing larvae of the commercially valuable Asian seabass.
To increase current knowledge on the nutritional value of natural prey organisms, the biochemical components of mainly three copepods (Acartia grani, Centropages hamatus, and Eurytemora affinis) from a marine pond system were analysed once a week from spring until late fall, over two years. The analysed components were total lipid, lipid class composition, total lipid fatty acid composition, free amino acids, total protein, protein-bound amino acids, pigment (astaxanthin and ß-carotene), and vitamins (A, thiamine, riboflavin, C, D3, and E). Copepod dry weight (DW), dry matter (% of wet weight), and ash content (% of DW) were also determined. The data are unique due to the homogenous content of copepods in the samples and the long time span of sampling. The copepods were characterised by moderate levels of lipids (6.9–22.5% of DW), with polar lipids accounting for 37.9 to70.2% of the total lipid. The most abundant fatty acids in total lipid (as % of total lipid) were 16:0 (palmitic acid, 10.8–17.1%), 20:5n-3 (EPA, 8.3–24.6%), and 22:6n-3 (DHA, 13.9–42.3%). The amount of 20:4n-6 (ARA) was generally low (0–2.6%), giving an EPA/ARA range between 7.5 and 49.5. The DHA/EPA ratio was between 1.0 and 4.9. Free amino acids (FAA) constituted between 4.3 and 8.9% of copepod DW, and varied with salinity. Glycine, taurine, and arginine dominated FAA, and the fraction of indispensable amino acids varied between 15.5 and 26.8%. Protein, as back-calculated from the protein-bound amino acids (PAA), amounted to 32.7–53.6% of copepod DW, and contained a stable fraction of indispensable amino acids (37.3–43.2% of PAA). Glutamine/glutamic acid, asparagine/aspartic acid, leucine, alanine, and glycine were the most abundant PAA. Astaxanthin was abundant in the copepods (413–1422 μg/g DW), while ß-carotene was not found. High but variable concentrations of vitamin C (38–1232 μg/g DW) and vitamin E (23–209 μg/g DW) were found, while vitamin A and D3 occurred in trace amounts or were not detected. Detectable levels were found for both thiamine (3.5–46.0 μg/g DW) and riboflavin (23.2–35.7 μg/g DW). The data may generate an important base for improvement of live feed enrichment emulsions or formulated feeds used during larval and early juvenile stages in marine fish culture.
Replicate groups of halibut larvae were fed to d 71 post-first feeding (PFF) either the marine copepod, Eurytemora velox, or Artemia nauplii doubly enriched with the marine chromist or golden algae, Schizochytrium sp., (Algamac 2000) and a commercial oil emulsion (SuperSelco). The fatty acid compositions of eyes, brains and livers from larvae fed the two diets were measured, and indices of growth, eye migration and skin pigmentation were recorded along with histological examinations of eye and liver. The docosahexaenoic acid [22:6(n-3); DHA]/eicosapentaenoic acid [20:5(n-3); EPA] ratios in Artemia nauplii enriched with the SuperSelco and Algamac 2000 were 0.4 and 1.0, respectively. The E. velox copepods were divided into two size ranges (125-250 and 250-400 microm) with the smaller size range containing the highest level of (n-3) highly unsaturated fatty acids (HUFA). The DHA/EPA ratios for the two size ranges of copepods were 2.0 and 0.9, respectively. The total lipids of eyes, brains and livers of larvae fed copepods had higher levels of DHA and lower levels of EPA than those of larvae fed enriched Artemia. The percentage of survival of the halibut larvae was significantly higher when copepods rather than enriched Artemia nauplii were fed, but larval specific growth rates did not differ. The indices of eye migration were high and not significantly different in larvae fed the two diets, but the percentage of larvae undergoing successful metamorphosis (complete eye migration and dorsal pigmentation) was higher in larvae fed copepods (40%) than in larvae fed enriched Artemia (4%). The rod/cone ratios in histological sections of the retina were 2.5 +/- 0.7 in larvae fed copepods and 1.3 +/- 0.6 in larvae fed enriched Artemia (P < 0.01). Histological examination of the livers and intestines of the larvae were consistent with better assimilation of lipid from copepods than lipid from Artemia nauplii up to 46 d post-first feeding. Thus, marine copepods are superior to enriched Artemia as food for halibut larvae in terms of survival, eye development and pigmentation, and this superiority can be related to the level of DHA in the feed.
The time to evacuate the gut was 40 minutes-3 hr, in contrast to gut evacuation times of 7-9 hr reported by other authors for herring larvae feeding on Artemia nauplii. The evacuation process was divided into 4 distinct phases with copepod prey. In non-feeding larvae the last 1-2 copepods were retained in the gut for several hours. -from Sport Fishery Abstracts
Copepods;Seed Production;larvae;fertilization techniques;zooplankton
Aquaculture in Taiwan annually produces billions of finfish fry. This is achieved mostly in outdoor pond systems where larvae feed on bloomed zooplankton. The zooplankton is dominated by copepods, mainly Apocyclops royi and Pseudodiaptomus annandalei (formally Schmackeria dubia). Zooplankton is produced in dedicated earthen ponds or as a by-product of finfish or shrimp culture. Such zooplankton, however, can contain pathogens such as viral nervous necrosis (VNN), parasitic Amyloodinium sp., and gill flukes such as Pseudorhabdosynochus sp. These pathogens have caused mass mortality of fish larvae, especially among larval groupers. A pathogen-free system to mass produce copepods is urgently needed. The copepods A. royi and P. annandalei have potential to be mass cultured in pathogenfree systems. The effects of food type, temperature, salinity, and density on the development and reproduction of these copepods were investigated. This chapter briefly describes the mass production of copepods and their application to finfish larval rearing on farms in Taiwan and reviews the status of copepod use for grouper larval culture.
Atlantic cod (Gadus morhua) show great potential for aquaculture, but much is unknown about their digestive capacity and efficiency. An integrated experiment
was performed on cod larvae to investigate the variability in digestive development in response to the quantity of lipid in
the rotifer enrichment. Survival, growth, behaviour, and digestive enzyme data from hatching to metamorphosis [0–450 dd (degree-days)]
were measured. Four treatments were used in triplicate: high lipid rotifer enrichment (HLRE), low lipid rotifer enrichment
(LLRE), green water, and unfed. Swimming activity and attacks (captures + misses) on prey were higher in the HLRE group at
100 dd than in other treatments, and this difference increased thereafter. There was no difference in digestive enzyme activity
between the unfed and greened treatments, while the LLRE larvae had lower activity levels than larvae fed HLRE by 100–150
dd for all enzymes assayed. The larvae in the unfed and green water treatments did not survive past 100 dd. All the LLRE cod
had died by 250 dd. Results suggest that a higher quantity of lipid in the rotifer enrichment will not only promote better
growth and survival in Atlantic cod larvae but appears to provide more energy, allowing larvae to capture more live prey.
The marine calanoid copepod Acartia tonsa has been continuously cultivated in the laboratory at the Danish Institute for Fisheries and Marine Research for over 70 generations. A description of the cultivation procedures is presented in this paper. Adult copepods are maintained in 200–450-l tanks and are fed the cryptophyte Rhodomonas baltica. The concentration of adult copepods is held between 50 and 100/l. Eggs are harvested daily and, on average, ca. 25 eggs are collected per female per day.
Newly-hatched Epinephelus coioides larvae were stocked in five 5-ton tanks at an initial density of 25,000 ind/tank. Copepod nauplii were propagated in four of these tanks by inoculating various densities (20 to 80 ind/l) of mixed copepodids of Acartia tsuensis, Pseudodiaptomus spp., and Oithona sp. three days before stocking larvae. Rotifers were added in these tanks on Day 7 at an initial density of 5,000 ind/l. Larvae in the remaining tank were fed rotifers (only) starting Day 2 at 5,000 ind/l. The feeding incidence, gut content, growth, and survival of larvae were better in tanks with higher density of copepodids (60-80 ind/l). These indices were lowest in larvae given rotifers only. Total n-3 HUFA of copepods was 2 to 3 times higher than rotifers. High percentages of 22:6n-3 (DHA) were detected in the fatty acid composition of Pseudodiaptomus (13%) and Acartia (24%) with DHA/EPA (20:5n-3) values of 1.4 and 2.6, respectively. By providing nauplii of copepods at the early feeding stage, an average survival of 3.4% at harvest (Day 36) was obtained in a pilot scale grouper seed production trial in three 10-ton tanks.
Over the past few years, great progress has been made in culturing cod larvae in indoor hatcheries using rotifers and Artemia or formulated feed as start-feed (intensive systems). However, when compared with natural systems based on copepods grown in seawater lagoons, the growth potential has not been fulfilled, and deformities of larvae and juveniles increase production costs. The deformities, which are seldom seen in natural systems, also constitute an ethical problem. The differences in growth and development of deformities in intensive and natural systems may be dependent, in part, on nutrition, but are caused by environmental conditions and early husbandry practises as well. To identify nutrients that may be deficient or in excess in live feed, we are in the process of screening the nutrient compositions of rotifers and Artemia grown or enriched on different feeds and comparing them with the composition of copepods and published requirements for larger fish. Replacing live food with formulated diets as early as possible is a goal of marine larval aquaculture. It is important that these diets contain protein which is available for the larvae and phospholipids that promote the absorption and transport of fat. The optimum macronutrient composition in diets for cod juveniles has been determined and can be extrapolated, with caution. to the larval stage. A problem in using formulated diets is the extensive leakage of nutrients as a result of the large surface area to volume and the short diffusion distance in the microparticles. Leakage leads to rapid loss of small, water-soluble molecules such as free amino acids, vitamins, and minerals, but extensive leakage of water-soluble protein has also been shown. The demand for protein available to the larvae, which probably will make the protein more water soluble, is therefore in conflict with the need to reduce protein leakage from the feeds. Development of feed production technology to prevent nutrient leakage is essential in order to make formulated diets a good alternative to live feed. (c) 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.
Copepods have often improved larviculture of marine fish species that are not easily reared using rotifers. One such species is Glaucosoma hebraicum. G. hebraicum larvae were reared on a combined diet consisting of equal numbers of cultured copepod nauplii and rotifers and a diet of rotifers only. Growth was significantly greater in larvae fed with the combined diet. Survival was 37% in the copepod/rotifer-fed larvae compared to 5% in the rotifer-fed larvae. Two separate methods of presenting copepod nauplii to Pagrus auratus larvae were also examined. Firstly, copepods nauplii were provided as the sole diet during the first feeding phase followed by rotifers. Secondly, rotifers were supplemented with copepod nauplii for an extended period. P. auratus larvae grew faster than rotifer fed controls in both trials. Larvae fed with the supplemented diet for an extended period grew fastest. There was no significant difference in survival and swim bladder inflation in P. auratus larvae, although those treatments with copepods in their diet were consistently higher. Improved larval growth and survival in both fish species were attributed to preferential selection of copepod nauplii and their high nutritional content.
Laboratory studies have shown that suboptimal prey concentrations during the first feeding usually result in slower growth and higher mortality. We investigated the growth, survival and foraging behaviour of Atlantic cod (Gadus morhua) larvae in different prey concentrations under laboratory conditions. Larvae were reared from hatching to metamorphosis (6 weeks post-hatch) on rotifers and/or Artemia nauplii at 250, 500, 1000, 2000, 4000, 8000 and 16,000 prey l−1. Once a week, standard length and myotome height were recorded and mortalities were monitored from day 15. Observations on feeding behaviour were recorded twice a week. Larvae reared at 4000–16,000 prey l−1 were significantly larger and had significantly higher condition indices than larvae from lower prey concentration (≤2000). Initially, specific growth rates (SGR) were significantly higher in larvae reared at higher prey concentrations (≥4000), but from 3 weeks post-hatch, no difference was found among treatments in SGR. Instantaneous mortality rates (Z) decreased in all treatments as the larvae grew. Survival was significantly lower for larvae reared at lower prey concentrations until week 3. Larvae reared at 250 and 500 prey l−1 did not survive beyond days 11 and 24, respectively. Survival of larvae was significantly higher at higher prey concentrations at weeks 2 and 6 post-hatch. Although survival of cod larvae at week 2 was similar among the three highest prey concentrations; survival at the end of the experiment (week 6) was higher, but not significantly, in the 4000 prey l−1 treatment than the other two treatments (8000 and 16,000 prey l−1). Swimming duration was significantly higher among larvae reared at lower prey concentrations. Larvae reared at higher prey concentrations (≥4000) showed higher orientation and captured success rates but lower attack rates than larvae reared at lower prey concentrations. Our results indicate that for intensive rearing of cod larvae, higher prey concentrations are required to sustain reasonable growth and survival than that have been reported for mesocosm studies.
Calanoid copepods of the genus Acartia have proven to be important in the diet of first feeding larvae of golden snapper, Lutjanus johnii, and mangrove jack, Lutjanus argentimaculatus, but it is difficult to reliably harvest these copepods from the wild. To overcome this problem, we present a simple method for the mass culture of Acartia spp. in the hatchery. This reduces the reliance on wild copepod populations and improves the coordination of larval rearing operations.Cultures of copepods were maintained in 100 and 1000 l tanks and fed daily with a mixed ration of algae, Rhodomonas sp., Tetraselmis sp. and Isochrysis sp., at a total algal cell density of 20,000 cells/ml. The cultures were lightly aerated and the salinity and temperature were maintained between 30–34 ppt and 28–32°C, respectively. The cultures were screened every 8 days to harvest adults and late-stage copepodids and to reduce contamination by rotifers and other undesirable zooplankton. The harvested copepods were used to restart the cultures. Using this method, more than 1000 adult copepods and late-stage copepodids per litre were produced from the 8-day culture cycle. This method has maintained productive cultures for more than 6 months and has been used to produce several batches of L. johnii fingerlings with survival rates of up to 40% at 21 days post-hatch. Adult copepods harvested from the cultures were stocked directly into larval rearing tanks. The copepods continued to breed in the larval rearing tanks and the resulting blooms of nauplii (up to 1.0/ml) were fed on directly by the larvae, eliminating the need to handle the easily damaged copepod nauplii.
Turbot larvae (Scophthalmus maximus L.) were fed with mass-cultured rotifers (Brachionus plicatilis) and copepods (Eurytemora affinis and Acartia tonsa). The fish preferred copepod nauplii to rotifers. Larvae reached metamophosis between days 30 and 36 at a length of 22 mm at temperatures between 13.2°C and 17.8°C. Survival rate was about 50% from day 3 to the end of metamorphosis. Postmetamorphosis growth was examined for 38 days under comparative feeding programmes using herring meat, living mysids, pelleted trout feed and combinations of trout feed plus mysids and herring meat plus mysids. Mean growth rates varied from 4.7% ¢ d−1 (herring plus mysids) to 4.1% × d−1 (trout dry feed). The addition of living mysids to the diets positively influenced the growth increase and food conversion rates.
The calanoid copepod Acartia tonsa was sampled throughout one generation to examine the fate of lipids during development in culture. Effects of dietary input were examined by feeding A. tonsa for at least one generation with specific monoalgal cultures. Four different algae were tested: the cryptophyte Rhodomonas baltica, the haptophyte Isochrysis galbana clone T-iso, the diatom Thalassiosiraweissflogii and the dinoflagellate Heterocapsa triquetra. Further, the effect of cold storage of eggs on the lipid composition of the newly hatched nauplii was examined. During development, the fatty acid composition changes from a tendency towards high levels of long-chain polyunsaturated fatty acids in the early developmental stages towards a tendency to accumulate more saturated and monounsaturated fatty acids in the later developmental stages. However, the content and composition of polyunsaturated fatty acids can be influenced by the dietary input. The highest ratio of 22:6n−3/20:5n−3 was achieved using H. triquetra or I. galbana. Higher levels of 20:5n−3 were achieved by feeding with R. baltica or T. weissflogii. I. galbana and T. weissflogii were particularly suitable for increasing levels of arachidonic acid (20:4n−6; AA) in A. tonsa.
A small paracalanid copepod, Parvocalanus sp., was isolated from Hawaiian coastal waters and subjected to a series of laboratory experiments to ascertain the effects of different combinations of microalgae (Chaetoceros sp. and Isochrysis sp.) on copepod survival, growth, and fecundity. Adult copepods exhibited the highest survival when fed Chaetoceros sp., whereas fecundity was highest (up to 21 offspring per adult per day) when Chaetoceros sp. was offered in combination with Isochrysis sp. The viability of nauplii produced by adult copepods fed Chaetoceros sp. was lower than from adults fed Isochrysis sp., in terms of survival and growth. Chaetoceros sp. was also an inferior diet for nauplii. Copepodid stages of Parvocalanus sp. exhibited similar survival on all diet combinations but had the greatest growth when fed Isochrysis sp. Large quantities of Parvocalanus sp. were also cultured routinely in 400-L tanks using a mixed diet of Chaetoceros sp. and Isochrysis sp. Copepod population densities fluctuated cyclically in these cultures, with nauplius densities ranging from approximately 1 to 30/mL. Up to 49 million Parvocalanus sp. nauplii were harvested per 400- L tank during preliminary 30-day trials to assess nauplius harvesting techniques. Red snapper, Lutjanus campechanus, larvae offered Parvocalanus sp. nauplii exhibited significantly greater survival to day 7 after hatching (50.3%) compared with larvae fed ss-type rotifers, Brachionus plicatilis (2.6%), and were significantly larger in size, confirming the efficacy of Parvocalanus sp. nauplii as a first feed for small subtropical marine fish larvae.
Spotted seatrout (Cynoscion nebulosus) were raised on rotifers, Artemia sp. nauplii, and dry feeds. On this diet sequence, they can grow to at least 110 g in 5 months, with feed conversions (ratios of dry feed weight eaten to wet weight gained by fish) of 0.78 to 1.55.
Six groups of Atlantic halibut, Hippoglossus hippoglossus L., larvae were offered calanoid cope-pods at different periods from days 11 to 25 after first feeding (1.13-3.20 mm myotome height) in order to establish at which stage normal pigmentation was determined. Artemia nauplii enriched with an oil emulsion were used prior to and after the copepod period. Control groups were fed on copepods or Artemia only. The Artemia diet initiated an earlier intake of food and higher initial growth compared to the copepod diet. After 50 days of feeding, the average dry weights of the fish fed on Artemia and copepods were quite similar to the copepod-fed fish, while the Artemia-fed fish were the smallest in size. The lowest frequency of normally pigmented juveniles was found in the Artemia-fed group (66.4%), while the copepod group showed almost 100% normal pigmentation. A significantly higher frequency of pigmentation was found in juveniles given a copepod diet close to the initiation of metamorphosis than those provided with an earlier copepod period of equal duration. A high degree of eye migration was found in all groups, but was lowest in the Artemia-fed group. The initial stage of eye migration was found to occur at a larger body size in fish given Artemia and copepods, or a copepod diet than in fish fed on Artemia alone. There was no significant correlation between eye migration and growth rates prior to metamorphosis, although the largest individuals exhibited the most complete eye migration. High pigmentation frequencies were obtained in fish with a low 22:6n-3:20:.5n-3 (DHA:EPA) ratio (< 1.0).
Populations of Acartia tonsa (Dana) and Centropages hamatus (Lilljeborg) were monitored in outdoor enclosures imitating the natural estuarine environment in northern Denmark from August 2003 to February 2004. A. tonsa was predominant in summer while C. hamatus dominated from October and onwards. Mean egg production was normally higher in C. hamatus as compared to A. tonsa and continued until late December before a decrease was observed. Hatching success remained high even in February at temperatures below zero degree indicating that no diapause eggs were produced. Further, the egg quality evaluated from the fatty acids (AA, EPA and DHA) and amino acid contents did not change markedly during the study period. From this observation it is strongly suggested that nauplii originated from copepod eggs produced throughout the monitored sampling period constitute an adequate live feed for fish larvae probably even year round.
In aquaculture, inclusion of copepod nauplii in the diet of larval fish may increase the number of fish species that can be successfully reared. Pelagic nauplii of calanoid copepods are more available as food items for most marine fish larvae than the predominantly epibenthic nauplii of harpacticoid copepods. However, sustained and substantial production of calanoid copepod nauplii is difficult. Intensive copepod cultures allow reliable and sustained production while utilising less space than extensive culture systems. Three intensive culture techniques for the temperate water estuarine calanoid copepod Gladioferens imparipes are described. These techniques comprise 60- and 500-l batch cultures and 1000-l semi-continuous cultures. Five hundred-litre cultures are part of a recirculating system that features automated nauplius collection and water treatment. Standardised nauplius production, expressed as number of nauplii produced per litre of culture vessel per day, is given for each technique. 878±46 nauplii/l culture vessel/day was achieved over 420 days for G. imparipes cultured in 500-l vessels. Standardised nauplius production is compared with published data from other copepod culture systems.
Despite the fact that the suitability of copepods as live prey for marine fish larvae is now well established, their use in aquaculture remains sporadic. Although of lower nutritional value, the relative ease of production of rotifers (Brachionus spp.) and Artemia nauplii continues to ensure their predominance. Studies in the literature have highlighted differences in the levels and ratios of fatty acids, lipid classes and pigments between copepods and traditional live prey. Such differences may have important consequences for fish larval nutrition. The consequences of poor nutrition during fish larval development may be obvious, for example deformities or malpigmentation, but in many cases may be obscure, as in affects on temperature tolerance or growth during later life stages. In some aquaculture systems, copepods are cultured in large quantities in outdoor, extensive or semi-intensive units. Intensive-rearing systems for copepods require further development. However, it is now established that intensive rearing on monoalgal diets does not result in severe deterioration of the nutritional value of the copepods, at least in terms of their highly unsaturated fatty acid (HUFA) content. In some cases, the provision of copepods for a short period of time during the larval stage is sufficient to ensure normal development. However, it remains to be demonstrated that the extra costs involved result in increased profits as a result of higher percentages of normally pigmented juvenile fish, improved growth and survival and reduced incidence of disease. This paper reviews the advances in production systems for copepods, their nutritional value as live prey for fish and their present and potential use in aquaculture.
Growth, feed conversion efficiency and frequencies of skeletal deformities were studied in juvenile Atlantic cod (Gadus morhua) that had been startfed on either rotifers (rotifer group) or zooplankton (zooplankton group). After metamorphosis, the fish were reared at four constant temperatures (7, 10, 13, 16°C) or moved successively from 16 to 13 and 10°C (T-step, average 13.2°C). The zooplankton group had a consistently higher growth rate at all the temperatures studied. Further, the zooplankton group had higher food intake (20%) and higher feed conversion ratio (1.65 vs. 1.31). In addition, a significantly higher incidence of skeletal deformities was found in the rotifer group (14.2%) compared with the zooplankton group (4.1%). After termination of the laboratory study, the fish were reared in sea pens under ambient conditions for 17 months. Final weights of the zooplankton group were consistently larger (between 12% and 14% larger depending on original temperature groups). To verify the growth results, we conducted a follow-up study where a single egg group was divided into two parts and fed either on rotifers or zooplankton. This study indicated similar growth differences as found in the first study. Overall, our data suggest that different startfeeding diets may be important for long-term growth, incidence of deformities and quality of juvenile cod. The use of zooplankton can greatly improve long-term growth and quality of cod juveniles. The study also highlights the advantage of using elevated temperatures in the juvenile phase as this will lead to significantly higher final weights in the adult stage.
Larvae of red-spotted grouper, Epinephelus coioides, were reared inoutdoor tanks with nauplii of copepods (mainly Pseudodiaptomus annandaleiand Acartia tsuensis) and/or rotifers, Brachionus rotundiformis. Grouperlarvae successfully started feeding on early stage nauplii even though theirabundance was as low as approximately 100 individuals l–1 andshowed better survival and growth thereafter compared to those fed withrotifers only. Incidence of feeding reached 100% on day 4 whennauplii were available and only on day 9 when rotifers were given alone.Larvae seemed to be poor feeders at the onset of feeding, attempting tocapture any food organisms in the tank water. Selective feeding ability oflarvae started from day 4 and the larvae then preferred to feed on medium-and large-size nauplii rather than on rotifers as they grew. Larvae appearedto have a better chance at surviving in the presence of early stage nauplii,which were probably caught more easily than rotifers.
The present paper studied the influence of different food regimes on the free amino acid (FAA) pool, the rate of protein
turnover, the flux of amino acids, and their relation to growth of larval turbot (Scophthalmus maximus L.) from first feeding until metamorphosis. The amino acid profile of protein was stable during the larval period although
some small, but significant, differences were found. Turbot larvae had proteins which were rich in leucine and aspartate,
and poor in glutamate, suggesting a high leucine requirement. The profile of the FAA pool was highly variable and quite different
from the amino acid profile in protein. The proportion of essential FAA decreased with development. High contents of free
tyrosine and phenylalanine were found on Day 3, while free taurine was present at high levels throughout the experimental
period. Larval growth rates were positively correlated with taurine levels, suggesting a dietary dependency for taurine and/or
sulphur amino acids. Reduced growth rates in Artemia-fed larvae were associated with lower levels of free methionine, indicating that this diet is deficient in methionine for
turbot larvae. Leucine might also be limiting turbot growth as the different diet organisms had lower levels of this amino
acid in the free pool than was found in the larval protein. A previously presented model was used to describe the flux of
amino acids in growing turbot larvae. The FAA pool was found to be small and variable. It was estimated that the daily dietary
amino acid intake might be up to ten times the larval FAA pool. In addition, protein synthesis and protein degradation might
daily remove and return, respectively, the equivalent of up to 20 and 10 times the size of the FAA pool. In an early phase
(Day 11) high growth rates were associated with a relatively low protein turnover, while at a later stage (Day 17), a much
higher turnover was observed.
In our study of the condition of larval cod (Gadus morhua) collected off southwest Nova Scotia in winter-spring, 1983, we (1) examined relationships between larval condition and ambient environmental conditions, and (2) compared the use of simple morphometric indices of larval condition and of multivariate statistics to obtain information relevant to larval condition. Twelve indices of relative condition were obtained, based upon seven measurements made on each larva, and a principal component (PC) analysis was performed on these condition indices. Most condition indices and the first PC were significantly correlated with numbers of nauplii and of zooplankters per m3 in the water column, which are direct measures of food available to the larvae, but not to less direct measures of environmental quality for the larvae, such as plankton displacement volume or chlorophyll concentration. Conventional indices based upon relations of dry weight or body height at the anus to length were most sensitive to environmental conditions. There was no apparent advantage in performing a multivariate analysis based upon a larger series of measurements.
The total lipid content in Artemia franciscana (21–23% ofdry weight (DW)) when enriched with either Super Selco or DHA Selco wastwice as high as in the adult copepods Temora longicornis and Eurytemora sp.(9–11% of DW). In Brachionus plicatilis the total lipid contentwas 11 and 6.6% for cultures growing at high and low growth rate,0.12 d–1 and 0.38 d–1, respectively. In thecopepodid stages I, II and III of Calanus finmarchicus the total lipid levelwas 12–13%, increasing to 24% in copepodid stage IV, Vand the adults. In T. longicornis and Eurytemora sp. the predominant fattyacids were DHA (22:6n-3), EPA (20:5n-3) and the saturated fatty acid 16:0,which constituted 40–45%, 21–24% and8–12% of total fatty acids, respectively. C. finmarchicuscontained the same dominant fatty acids. In both the cultivated live feedorganisms DHA, EPA and 18:1 were the predominant fatty acids. In A.franciscana the content of these fatty acids varied according to theenrichment medium and in B. plicatilis according to the growth rate.
Studies were carried out on the proteolytic activity of the fry of common carp, rainbow trout, grass carp, and whitefish,
as well as on the activity of digestive organs of adult common carp and rainbow trout. Activity of exogenous enzymes in relation
to endogenous ones was assessed on the basis of the proteolytic value of fish food and the activity of digestive organs. It
was found that the share of proteolytic enzymes of natural food in the digestion process in fish was high. Beginning from
a weight of 50–100 g for common carp and 10 g for rainbow trout, the relation between the daily enzymatic ration and the weight
of fish indicates the cooperation of an approximately constant amount of exogenous enzymes.
Sea bass (Dicentrarchus labrax) larvae were weaned at day 25 with microparticulated diets in which 10% of the nitrogen supply had different molecular forms: amino acid mixture (SLAA), casein hydrolysate (SLH) or fish meal (SLP). The control group (LP) was fed live prey. No difference was observed in larval growth between the weaned groups, but the survival was significantly higher in the SLH group. Trypsin secretion was stimulated in the SLAA group, whereas the SLH diet reduced the secretion from the exocrine pancreas. The activity of the leucine-alanine peptidase, located in the cytosol of enterocytes, remained high in all weaned groups. However, the activity of the peptidases of the brush border membrane increased during the development phase in the control group. These results suggest that weaning with a classic compound diet delays enterocyte differentiation by maintaining the larval features of digestion. A compound diet containing protein hydrolysate can attenuate the delay of intestinal maturation.
In the natural food web, zooplankton constitutes a major part of the diet for marine fish larvae and it is generally believed that copepods can meet the nutritional requirements of fish larvae. In this study, different copepod species were analysed for total lipid content, fatty acid and protein content and used in first feeding experiments with halibut larvae (Hippoglossus hippoglossus L.) together with enriched nauplii and juvenile stages of Artemia franciscana. Special attention was paid to the DHA content in both the live food organisms and the fish larvae.
A protein preparation labelled by incorporation of [U]14C-AA was hydrolysed to various degrees and administered to a teleost fish larva (Atlantic halibut, Hippoglossus hippoglossus L.) by tube-feeding, and its post-administration utilisation was studied. Three treatments were prepared: IntP—intact protein, PHP—pepsin-hydrolysed protein, and HHP—highly hydrolysed protein (using pepsin, trypsin, endoproteinase Glu-C, Asp-N, and Pro-C). At small doses (11.4±1.5 μg larvae−1), the intact protein (IntP) was digested and absorbed to 36±5.5%. However, the relative absorption efficiency of the intact protein was reduced as the dose increased. Absorption efficiency was higher when the protein was hydrolysed prior to feeding the larvae and was constant at 63% (R2=98) independent of degree of proteolysis and dose (ranging from 3.5 to 35 μg larvae−1). The initial absorption rate increased with the degree of hydrolysis. Calculations based on data collected during the first 30–120 min show that the absorption of PHP and HHP into extra-intestinal body tissues was 2.2 and 3 times as fast, respectively, as that of intact protein. However, the rates of absorption did not influence the distribution of absorbed AA into either catabolism or anabolism, as all larvae, independent of which protein solution they were given, catabolised 42±7% of the absorbed AA, and accumulated 49±6% into the body tissue, during the 20 h post-feeding incubation period.
Two separate studies investigated the effect of dietary phosphatidylcholine (PC) on the assimilation of ingested free fatty acid (FFA) into the tissues of 28-day-old gilthead seabream larvae. Two squid meal based microdiets (MD), labeled with free [1-14C] 18:1n−9, were prepared that were identical in their nonlipid fractions and total lipid levels but differed in their lipid compositions. The control MD contained, by dry weight (DW), 10% capelin oil while the treatment MD comprised of 7.5% capelin oil and 2.5% di-stearylphosphatidylcholine. In the first study, the MDs were fed to seabream larvae over 14 h followed by 10 h of food deprivation in the dark. Larval samples were taken after 1, 8, 14 and 24 h and the resultant distribution of radioactivity in whole body lipid fractions was determined. Starting at 8 h and reaching a maximum after 14 h of feeding, larvae fed the PC diet demonstrated higher (P<0.05) levels of radioactivity compared to the control larvae, in their polar (1179±72 and 595±70 dpm larva−1, respectively) and free fatty acid fractions (460±66 and 201±40 dpm larva−1, respectively). This suggested that both the assimilation and ingestion rate in the PC larvae increased over the control fish after 8 h of feeding. During the 10 h of food deprivation, radioactivity in the triacylglycerol (TAG) fraction of the PC larvae decreased by 37% while radioactivity in the control fish TAG decreased by only 16%. Apparently, a considerable amount of this 14C-label was mobilized for membrane lipid synthesis as evidenced by increases of 14C-label in the PL class of the PC and control larvae that reached 1447±62 and 737±49 dpm larva−1, respectively.
The present work reviews the significance of lipids at different early stages of marine fish larvae. Lipids in broodstock nutrition are considered to be important for the quality of the larvae. Lipids affect the spawning and the egg quality of many fish species and a deficiency in (n−3) highly unsaturated fatty acids (HUFA) in broodstock negatively affects fecundity, fertilization rate and hatching rate of the species studied. Lipids as a source of energy at the embryonic and larval stage (before first-feeding) are evaluated in relation to other sources of energy such as protein and carbohydrates. After hatching and prior to first-feeding, some marine species show a preference in catabolizing phosphatidylcholine, whereas phosphatidylethanolamine tends to be synthesized. The effect of long-term (LT) and short-term (ST) enrichment techniques on the lipid composition of rotifers has been documented using various marine oils/emulsions. The quantitative and qualitative lipid class and fatty acid composition of diets influenced the lipid and fatty acid composition of both LT- or ST-enriched rotifers. The nutritional improvement of Artemia is also important and may follow the general methods used for rotifers. The functions of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) during early stages of marine fish larvae are apparently different. High amounts of EPA in relation to DHA may create an imbalance in the structural composition of the phospholipids, which could affect the normal growth and the quality of the larvae. Turbot larvae tended to exhibit lower pigmentation success with lower DHA:EPA ratio in the total lipid fraction of the larvae, especially when the absolute amounts of EPA were high compared to those of DHA (in the total lipid and phospholipid fraction of the larvae). Considerable research is necessary to clarify many aspects regarding the function of these fatty acids, especially how their content at the egg stage can affect further requirements for normal growth and survival.
Despite the scientific and commercial interest that Atlantic halibut has received over the past decade, little is known of the ontogeny of its digestive tract during larval development. The provision of enriched Artemia as prey has been associated with incomplete metamorphosis while improved development has been achieved using wild plankton e.g., copepods. The aim of the present study was to investigate whether there was any variation during development in the ability of the larvae to digest and incorporate Artemia or copepods. Groups of larvae fed either Artemia enriched with an oil emulsion (Super Selco™) and with a dried protist Schizochytrium (Algamac 2000™) or with a marine calanoid copepod (Eurytemora velox) were sampled weekly from the end of yolksac resorption to the completion of metamorphosis. The sites of absorption were visualised by the presence of vacuoles in the epithelial cells of the digestive tract's mucosa. During the first 30 days of exogenous feeding, before the stomach had formed, there were small inclusions on the apical side of the rectal epithelial cells in both groups. Between 30 and 50 days post first-feeding, at the time when the stomach was differentiating with the appearance of gastric glands, and the four pyloric caecae were starting to elongate, numerous supranuclear vacuoles were observed in the mid- and hind-gut epithelial cells of the copepod-fed group. The rectal epithelial cells showed lipid vacuoles that filled their apical ends suggesting significant absorptive activity. By contrast, few vacuoles were present in the rectum of the Artemia-fed larvae. By the end of metamorphosis (up to 83 days post first-feeding), the copepod-fed larvae had an adult-like digestive tract with functional stomach and highly absorptive intestine. At the same age, the Artemia-fed larvae showed that the rectum was still the major site of absorption; this is a typical larval feature. Furthermore, observations of the gut's content confirmed the poor ability of the halibut larvae to digest Artemia in comparison to copepods. Indeed, while no individual copepod could be identified in the digestive chyme past the mid-gut of these larvae, partially digested Artemia could be seen as far as the anus in those fed on Artemia. Although the rate of development and of differentiation of the digestive tract of first-feeding halibut larvae appeared unaffected by the nature of their prey items, our results show a difference in the absorption sites of copepods vs. Artemia. These findings are of considerable significance to the rearing techniques used in the commercial production of halibut juveniles.
Turbot larvae were reared in an 8.5-m3 enclosure and offered the rotifer Brachionus plicatilis and natural zooplankton at densities between 150 and 1600 zooplankters per l. Young larvae were found to select for copepod nauplii, while in older larvae a selection for juvenile and adult stages of Paracalanus sp., Centropages sp. and harpacticoids was found. Size selection was also demonstrated. In spite of being the most numerous potential prey, both juveniles and adults of Acartia sp. were ingested in small quantities by the turbot larvae. Selection was prominent during periods of high prey densities, indicating that the larvae were optimizing energetic intake. Reasons for the observed selections are discussed. An insufficient zooplankton supply the first week posthatch resulted in negative specific growth rates (between −6.9% and −21.9%). Recovery of growth then occurred when prey concentrations increased. Survival was estimated to be 11% at day 27 posthatch, and mortality seemed to be size-specific. Ingestion by the larval population predicted by an energy model appeared to closely fit variations in prey availability. The calculated specific ration decreased from 244% in young larvae to 41% in larvae close to metamorphosis. Gross growth efficiency (K1) was estimated to increase from 5.6% initially to 34.0% in premetamorphosing larvae. Negative values of K1 were recorded in young larvae, but growth efficiency recovered when the feeding conditions improved. The energy model is considered to produce realistic estimates of larval prey consumption.
Histological observations were made in common carp larvae in order to understand the origin of the phospholipid (PL) requirement of fish during their young stages. Larvae were fed for 6 or 8 days after start-feeding on semi-purified diets containing peanut oil and supplemented with or without different PL fractions enriched in phosphatidylcholine (PC) or phosphatidylinositol (PI). A group of larvae was also fed Artemia nauplii. Dietary PL deficiency was associated with an accumulation of fat droplets in the enterocytes of the anterior intestine, an increase in height of mucosal epithelium, a reduced total liver volume and mean hepatocyte volume. In contrast, diet supplementation with PC from hen egg yolk or from soybean prevented the intestinal steatosis and resulted in larger liver volume and larger hepatocyte volume. Larvae fed Artemia showed the same features as larvae fed PC-enriched diets. Hydrogenated PC also prevented the intestinal steatosis but resulted in small liver and hepatocyte size. Larvae fed PI-enriched diets exhibited intestinal steatosis, although less systematically than larvae fed PL-deficient diets, and reduced liver and hepatocyte size. Results support previous opinions that PL are needed for the absorption of neutral lipids although their beneficial effect appears to be independent of their emulsifying properties. The limiting stage seems to be the synthesis and exportation of chylomicrons or very low density lipoprotein (VLDL) by the enterocytes and not the intraluminal formation of micelles. PC appears to have a specific role for chylomicrons and VLDL synthesis and secretion, as in mammals. The reduced liver and hepatocyte size in the absence of PC could result from a decreased energy supply due to poor lipid absorption.
Fatty acids, vitamin A and thyroid hormone have all been shown to affect development of flatfish larvae and they are ligands to nuclear receptors that participate in the control of development. Our hypothesis was that one of these factors or an interaction between them may be the cause of abnormal development of flatfish larvae. Atlantic halibut larvae were fed either DHA-selco-enriched Artemia or copepods from first feeding. In fish that had been fed Artemia, only 7% had normal pigmentation and 10% normal eye migration. The numbers for fish fed copepods were 68% and 88%, respectively. Malpigmented fish fed Artemia were depigmented, while those fed copepods had ambicoloration. The differences in development were probably nutrient dependent, since all other conditions were similar for the two groups. Larvae fed copepods had markedly higher body levels of docosahexanoic acid (DHA, 22:6n−3) and eicosapentaenoic acid (EPA, 20:5n−3) and lower levels of arachidonic acid (ARA, 20:4 n−6) than larvae fed Artemia. The DHA/EPA ratio was similar in the two groups, but the EPA/ARA ratio was more than four times higher in larvae fed copepods than in larvae fed Artemia. Larvae fed copepods had higher body levels of total retinol than larvae fed Artemia, but the difference was due to higher levels of the storage forms, retinyl esters, whereas the levels of free retinol and retinal were similar in the two groups. The level of iodine was 700 times higher in copepods than in Artemia and 3–4 times higher in larvae fed copepods than in larvae fed Artemia. There was a significantly higher level of T4 in larvae fed copepods during the “window of opportunity”, 15–30 days after first feeding. In an experiment where Atlantic halibut larvae were fed Artemia enriched in iodine up to the levels found in copepods, there was a significant effect on the body level of iodine and a non-significant tendency of higher levels of thyroid hormone, but no effect on pigmentation or eye migration. It is concluded that Artemia probably offers a sufficient access to vitamin A precursors to meet the larval requirement. More research should be done to elucidate possible effects of iodine on development of Atlantic halibut larvae. Fatty acid composition is still the most likely candidate for causing abnormal development in Atlantic halibut larvae.
Spotted seatrout (Cynoscion nebulosus) pond culture trials (52) were conducted on the central Texas coast from 1983 through 1988. All ponds were stocked with 2-day-old larvae at 45 000 to 2 075 000/ha, 9 to 28 days after initial filling and fertilization. Zooplankton, dissolved oxygen concentration, salinity, and temperature were routinely sampled throughout the culture period. Ponds were harvested 20 to 30 days after stocking. Stepwise multiple regression analyses were used to examine the effect of 38 independent variables associated with stocking density, the length of the culture period, fertilization, water quality, and zooplankton densities on percent harvest, number of fish harvested/ha, and kg of fish harvested/ha day−1 of culture. Mean temperature, mean polychaete larvae densities for the culture period, and minimum dissolved oxygen concentration observed explained 69% of the variance in percent harvest. Mean temperature, stocking density, and mean polychaete larvae densities in the second, third, and fourth week after stocking explained 79% of the variance associated with number of fish harvested/ha. Variation observed in kg of fish harvested/ha day−1 of culture was best explained (R2 = 0.76) by mean temperature, stocking density, and mean polychaete larvae densities in the first and fourth week after stocking. Polychaete larvae density, especially during the latter stages of culture, was statistically the most important factor associated with production of spotted seatrout from larvae to ≈ 30 mm TL fingerlings.
The small calanoid copepods Bestiolina similis and Parvocalanus crassirostris (Paracalanidae) are compared to Acartia sinjiensis, a species of the copepod genus most commonly cultured to provide larval diets for tropical snappers and groupers. All species are easily maintained in culture, though cultures of Acartia spp. are easier to establish because of the positive phototactic behaviour of this genus. B. similis and P. crassirostris are smaller than A. sinjiensis, and consequently, their developmental stages are more suited to larval fish requiring small prey items. In addition, siphon-avoidance experiments indicated that adults of these species were more vulnerable to predation, though this was not the case for juvenile copepods. Egg production was maximised with larger algal cells, especially Rhodomonas sp. and Heterocapsa niei: B. similis fed H. niei achieved the highest egg production rates (48 eggs female−1 day−1). Lipid composition of all species was low and variable (11–26 mg g−1) under our culture conditions, in contrast to results from temperate copepod species or from wild-caught copepods. All three species studied had DHA/EPA/ARA ratios that met or exceeded those recommended for marine larval fish feeds (DHA/EPA/ARA-14:3:1, 20:9:1 and 25:6:1 for A. sinjiensis, P. crassirostris and B. similis, respectively). On the basis of size of developmental stages, susceptibility to predation, growth rate and nutritional composition, B. similis was the best candidate for larval fish diets.
Comparison of copepods and enriched Artemia as feeds for larval mahimahi, Coryphaena hippurus
- S Krual
- H Ako
- K Brittain
- A Ogasawara
- R Cant
- T Nagao
Krual, S., H. Ako, K. Brittain, A. Ogasawara, R. Cant-rell, and T. Nagao. 1991. Comparison of copepods and enriched Artemia as feeds for larval mahimahi, Coryphaena hippurus. P. Lavens, P. Sorgeloos, E. Jaspers, and F. Ollevier, editors. European Aqua-culture Society, Special Publication No. 15. Larvi 1991 – Fish and Crustacean Larviculture Symposium. European Aquaculture Society.
Rearing of Puvanendran, V. and J. Brown. 1999. Foraging, growth and survival of Atlantic cod larvae reared in different prey concentrations
- D Kuhlmann
- G Quantz
- U Witt
Kuhlmann, D., G. Quantz, and U. Witt. 1981. Rearing of Puvanendran, V. and J. Brown. 1999. Foraging, growth and survival of Atlantic cod larvae reared in different prey concentrations. Aquaculture 175:77–92.
Survival and growth of larval spotted seatrout (Cynoscion nebulosus) in relation to temperature, prey abundance and stocking densities
- Taniguchi