Marine Behaviour and Physiology

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Zoeae of Paralithodes camtschatica were positively phototactic to white light intensities above 1 x 10(13) q cm-2 s-1. Negative phototaxis occurred at low (1 x 10(12) q cm-2 s-1), but not high intensities (2.2 x 10(16) q cm-2 s-1). Phototactic response was directly related to light intensity. Zoeae also responded to red, green and blue light. Zoeae were negatively geotactic, but geotaxis was dominated by phototaxis. Horizontal swimming speed of stage 1 zoeae < 4 d old was 2.4 +/- 0.1 (SE) cm s-1 and decreased to 1.7 +/- 0.1 cm s-1 in older zoeae (P < 0.01). Horizontal swimming speed of stage 2 zoeae was not significantly different from > or = 4 d old stage 1 zoeae. Vertical swimming speed, 1.6 +/- 0.1 cm s-1, and sinking rate, 0.7 +/- 0.1 cm s-1, did not change with ontogeny. King crab zoeae were positively rheotactic and maintained position in horizontal currents less than 1.4 cm s-1. Starvation reduced swimming and sinking rates and phototactic response.
 
Many planktivorous fishes forage in currents, where they actively maintain position and visually strike at current-entrained zooplankton. In general, the zooplankton are wafted by the foraging fish at a rate equivalent to the current velocity. From a fish's viewpoint the plankton approach either head-on or offset at varied distances from the fish's position. We present a model that describes the relative motion of particles as they approach and pass a foraging fish at different offset distances, and the rate of change in apparent size as they close on a fish. In addition, a series of experiments of fish feeding on plankton in a flume at increasing current velocities revealed that two basic tactics are utilized. At low current velocities (<10-14 cm s-1), the fish swims toward the prey, whereas at higher current velocities the fish tends to fall back with the current to capture a prey item. The model and experimental results are discussed in terms of the visual problems associated with the detection and tracking of items in motion.
 
Schematic of 200 L bubble curtain tank for maintaining krill in captivity. 
Euphausia superba. Measurements of krill maintained in captivity and freshly caught krill (AE 1 SE). (A) Mean wet weight of krill maintained in the laboratory (no data for field sample). (B) Mean total body length. (C) Antennae length expressed as percentage body size. (D) Antennule length expressed as percentage body size. 
superba. Displays the coefficient of variation of the percentage length data for antennae and antennules for krill maintained in captivity (2002) and freshly caught krill from the field (1988)
Krill in captivity endure spatial restrictions, regardless of the size or shape of tank used. Visual inspection of freshly caught and captive animals suggests that their appendages, particularly the antennae and antennules, are often subject to injury. We have developed a novel method for reducing physical damage to captive krill based on their reported reaction to feeding whales. This method involves creating a bubble curtain that keeps the krill in the centre of the tank and away from potentially damaging hard surfaces. There was no difference in the length of the antennae between any of the captive animals. Trends in the data suggest that the antennules of krill maintained in a 200 L bubble curtain tank and a1000 L holding tank, were longer and less variable in length, than for krill in a 200 L tank with no bubble curtain. Freshly caught krill from the field were found to have damage to both antennae and antennules. The implications of these findings for husbandry of krill and for behavioural studies in the laboratory are discussed.
 
Southern catfish juvenile (37.6–65.9?g) were fasted for two weeks and fed with cutlets of freshly killed loach species at 2% body mass per meal twice daily (06:00 and 18:00) for four days at 27.5°C. Metabolic rates were measured during the fasting and feeding periods and all metabolic rates were adjusted to a standard body mass of 1?kg using an exponent of 0.75. The aim of this study was to investigate the effect of fasting and repeat feeding on the resting metabolic rate and the feeding metabolic rate. The results demonstrated that the standardized value of the resting metabolic rate gradually decreased from 69.6?±?2.7 (means?±?S.E.) to 42.8?±?2.3?mgO2?h -1 during the two weeks of fasting. The peak feeding metabolic rate and average metabolic rate of each feeding (12?h) gradually increased with repeat feeding before leveling off. The results of this study suggest that southern catfish can regulate digestive function and gradually alter the characteristics of metabolism according to the availability of a food resource.
 
The effect of salinity and ionic composition of ambient water on the mortality of the Ponto-Caspian gammarid amphipod Dikerogammarus haemobaphes (Eichwald, 1841) was measured in the laboratory and an osmoregulatory curve plotted. A three-day experiment showed that salinities both higher (15, 20 PSU) and lower (0.1, 3.5 PSU) than 7 PSU reduced survival. Salinity levels of 0.1 and 20 PSU were lethal after 20 and 55 h of exposure, respectively. Among the ions analysed (Cl−, [Inline formula], Na+, K+, Ca2+, Mg2+), Cl− and K+, and the ratios of Na+/K+ and Na+/Cl− had the greatest influence on the mortality of D. haemobaphes. Mortality was zero in waters where the concentrations and ratios of these ions most closely resembled those prevailing in the Caspian Sea. The osmoregulatory curve shows that D. haemobaphes is a eurytopic species i.e. osmoregulation is hyperosmotic within the salinity range of 0.1–20 PSU. The results of this study indicate ways in which inherent physiological capabilities affect the ability of an organism to tolerate environmental conditions outside its historical range. The results suggest some ways in which anthropogenic changes may have affected the spread of this species beyond its original range.
 
M. chilensis. Clearance rate during the intoxication-detoxification periods of specimens of collected from populations with different histories of PSP exposure. (A) Corral, Valdivia (without PSP exposure) and (B) Melinka, Aysén (frequent PSP exposure). The values represent the average ± the standard error. 
M. chilensis. Intoxication-detoxification dynamics in two populations with different histories of PSP exposure. Corral, Valdivia (without PSP exposure) and Melinka, Aysén (frequent PSP exposure). The values represent the average ± the standard error. 
Individuals of Mytilus chilensis with different histories of exposure to paralytic shellfish poisoning (PSP) were exposed to a diet containing the dinoflagellate Alexandrium catenella. Feeding and intoxication–detoxification dynamics were evaluated over a period of 12–16 days. Feeding activity was reduced during the first days of exposure, followed by a period of recovery from day 5 to the end of the experiment. Mussels from Corral population (no history of PSP exposure) exceeded the concentration of 80 μg STX eq. 100 g−1 tissue, although filtration activity was significantly lower compared with individuals from Melinka (frequent PSP exposure). The higher feeding activity and the lower degree of toxin accumulation in the Melinka population appear be associated with frequent exposure to PSP in the natural environment. The use of A. catenella as food resource and the capacity of a rapid intoxication of both populations showed that M. chilensis is an adequate indicator for early detection of PSP.
 
Map of Cananeia region, collection site of juveniles of F. paulensis used in the experiments. 
Survival (%) of juvenile shrimp F. paulensis (class 49.4 ± 4.3 mm) submitted to different salinity levels in water. 
Specific oxygen consumption of F. paulensis at different salinity levels. 
Mortality (%) of juvenile shrimp F. paulensis (class 49.4 ± 4.3 mm) in the first 12 h sub- jected to different salinity levels in water.
It is of paramount importance to study salinity tolerance of commercially important crustaceans, such as the pink shrimp Farfantepenaeus paulensis to determine possible mortality causes in the wild and in aquaculture in oligohaline waters. The aim of this study was to determine the lethal salinity concentration (LC50) for juvenile pink shrimp F. paulensis and measure its oxygen consumption and ammonia excretion at different salinity levels. Shrimp of two length classes (49.4 ± 4.3 and 78.5 ± 5.5 mm) were placed in 10-L containers and exposed to salinity levels of 35, 30, 25, 20, 15, 10 and 5. The experiments were tripled, with seven shrimp in each container. The average lethal concentration (LC50s) for an exposure of 24 h was 13.33 (11.26–15.78) and 10.26 (8.60–12.64), respectively, for the two classes of juveniles. For an exposure of 48 h, LC50s were 12.71 (10.68–15.12) for the larger animals and 9.20 (7.34–11.52) for the smaller ones. There was an inverse relationship between salinity and rates of oxygen consumption and ammonia excretion. The average reduction in specific oxygen consumption in salinities 20, 25 and 30 showed a decrease in metabolic rate of 63, 80 and 82%, respectively, in relation to salinity level 0. The same occurred for the averages of ammonia excretion at salinity levels of 15, 20, 25, 30 and 35, which represented low metabolic rates of 57, 61, 70, 71 and 74% respectably in relation to salinity level 0.
 
Sexually mature male and female spiny damselfish, Acanthochromis polyacanthus (Pomacentridae) were introduced to resident fish of both sexes in paired encounter trials and the effect on activity, agonistic behaviour and plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) in males, and T and 17β-estradiol (E2) in females, and cortisol in both sexes was determined. Introduced males showed suppressed levels of T in the presence of both resident males and females, whereas resident males showed elevated T in response to introduced males but not females. Plasma 11-KT levels were unchanged in either resident or introduced males. Resident males showed increased activity in the presence of males but not females. Resident females showed an increase in activity when paired with introduced females and greater aggressive behaviour towards females than males. There were no differences in plasma hormone levels in either resident or introduced female fish. Plasma cortisol levels were low in all fish and stress effects did not appear to account for differences in T levels in males. The results of the present study show that elevations in plasma T levels in resident male spiny damselfish are associated only with male presence but that suppression of T in introduced fish occurs irrespective of the sex of the resident. In contrast resident females, which show stronger evidence of aggressive behaviour do not show changes in plasma androgen levels. This suggests that aggressive behaviour in male and female fishes may be mediated by different endocrine pathways. Yes Yes
 
This study reports the 96-h LC50 value and tissue copper (Cu) levels and biochemical changes in juvenile fish (Acipenser persicus) exposed to 0.026 mg/l ambient Cu for 1, 7 and 14 days. It then examined the recovery of the same parameters after placing the juvenile fish in clean water for a further period of 28 days. The intestine, kidney and gill Cu levels, plasma glucose, total protein, triglyceride, cortisol, triiodothyronine and thyroxine concentrations, liver protein contents, liver catalase, superoxide dismutase (SOD) and glutathione S-transferase activities were studied. The 96-h LC50 value of Cu was 0.502 mg/l for juvenile A. persicus. The results indicate that Cu exposure produced significant accumulations of Cu in gills and kidney over the treatment time. Sublethal dose of Cu resulted in a short-term increase in plasma glucose, total protein and cortisol levels that decreased with time. After the 28-day recovery phase, there were significant differences in kidney Cu levels and triglyceride concentrations as well as SOD activities between recovery fish treatments and their control groups on day 42. The 28-day recovery phase caused significant decreases in total protein levels and SOD activities of Cu-exposed fish on day 42 compared to day 14. The results suggest that 28 days are insufficient for complete recovery to Cu exposure by juveniles and a longer period would be required for full recovery. Moreover, the study showed that the recovery phase following Cu exposure could change biochemical parameters to levels that are not close to those seen during exposure or control levels.
 
Empirical studies suggest that individuals with a high resting metabolic rate (RMR) are at an advantage under favourable conditions because they digest food rapidly and exhibit a greater growth potential. However, we hypothesised that high-RMR individuals have less energy available for digestion under hypoxia than they do under normoxia due to their relatively high maintenance cost. To test this hypothesis, we measured the RMR and postprandial metabolic responses of juvenile southern catfish, Silurus meridionalis, under normoxia and moderate hypoxia. The results provided the first evidence that (1) both the RMR and postprandial metabolic rate showed repeatability across different water [O2] conditions and (2) the correlation between the RMR and postprandial metabolic traits differs with changes in environmental factors (water [O2]). These findings suggested that the digestive advantage of individual southern catfish with a high RMR is impaired under hypoxia.
 
Experimental set-up for presenting computer-generated visual stimuli to crabs. The visual stimuli were generated by two computers (550 MHz Pentium III PCs), connected by a hardware link that ensured programs ran in synchrony. Programs were loaded on both computers, but were initiated by a key stroke from the master computer alone. Each computer drove a LCD data projector (Panasonic PT-L291) whose images were back-projected onto a translucent screen that surrounded the crab. The crab was clamped in the centre of the cylinder, prepared either for intracellular recording (this diagram) or for eye movement recording. In this way, images could be projected over an angular range relative to the crab's eye of 240 in azimuth (120 for the image from each projector) and 100 in elevation. In some experiments, the cylindrical screen was replaced by two flat screens, which formed two sides of an equilateral triangle with the crab at its centre. Neural responses (V m), monitors of intracellular current injection (I mon) and the screen coordinates of the visual stimuli (X pos) were stored on a PC (266 MHz Pentium II) using a computer interface (CED 1401plus).
Gains (AE95% confidence intervals) of optokinetic responses to movements of patterns of computer-generated stripes simulating a combination of rotation and translation. As shown in the diagram above the histogram, the rotational stimulus was a continuous sinusoidal movement (10 peak-to-peak, 0.1 Hz). To this was added a translational stimulus consisting of alternate backward and forward movements of constant velocity (0.04 s À1 when measured at 90 to the direction of simulated motion) but variable amplitude, with interposed periods where there was no added translation. The amplitude of the translational components of the stimuli were 12.5 cm, 6.5 cm and 2.5 cm, which corresponded to translations of 19.8 , 10.3 and 4.0 , respectively, when measured at right angles to the direction of simulated motion. The left and right hand blocks of the histogram (labelled 'Backward' and 'Forward') show gains of the responses when forward and backward translational movements were superimposed on the rotation, while the central block (labelled 'Stationary') shows gains of the responses when the stimulus was pure rotation. For each amplitude of superimposed translation, responses to motion where the translational movement was in phase with the rotation (R þ T) were separated from those where they were in antiphase (R–T). The pattern had a mean intensity of 54 cd m À2 , and contrast ratio of 15 : 1. Data based on responses of 16 crabs (Cardisoma). n ranged from 192 cycles (when the amplitude of the translational component was lowest) to 640 cycles (when the amplitude of the translational component was highest). Since response gains showed no significant variation under any of the experimental conditions, it can be concluded that, under these conditions of high light intensity and contrast, the crabs successfully separated the translational and rotational components of the simulated optic flow by showing compensatory eye movements to only the latter.  
Distortion of patterns of stripes so that they create realistic simulations of rotation and translation at the eye of the crab. A, Correction required to produce patterns of constant stripe width on the curved screen. B, Use of 4-bit grey scale to give the illusion of smooth movement. See text for details.  
A system for the back projection of computer-generated visual images onto a screen or screens that cover 240° of the horizontal visual field is described. Its applicability for the study of crab vision is tested by comparing the frequency response of the optokinetic response of the land crab, Cardisoma guanhumi, to sinusoidal oscillation of computer-generated striped patterns and a real striped drum. Significant differences were observed only at the low end of the frequency spectrum. The flexibility of computer-generated visual stimulation and its advantages for the study of optic flow are illustrated by experiments that: (a) demonstrate how well crabs separate the translational and rotational components of optic flow by showing compensatory eye movements to only the latter; (b) show that the ability to compensate for rotation is not impaired by combinations of rotation and translation; (c) show that motion parallax cues are used in addition to previously-described global cues for making the distinction between rotation and translation. Finally, the use of these methods in a successful search for visual interneurones sensitive to optic flow stimuli is demonstrated for the shore crab, Carcinus maenas.
 
The ability to regenerate lost tissues, organs or whole body parts is widespread across animal taxa; in some animals, regeneration includes transforming a remaining structure to replace the one that was lost. The transformation of one limb into another involves considerable plasticity in morphology, physiology and behavior, and snapping shrimp offer excellent opportunities for studying this process. We examined the changes required for the transformation of the small pincer to a mature snapping claw in Alpheus angulosus. First molt claws differ from mature claws in overall shape as well as in morphology related to snapping function; nonetheless, shrimp with first molt claws do produce snaps. While most shape variables of second molt claws do not differ significantly from mature claws, the plunger (structure required for snap production) does not reach mature size until the third molt for females, or later for males. Thus, the pincer claw can be transformed into a functional snapping claw in one molt, although both the underlying morphology and superficial shape are not fully regenerated at this stage. The rapid production of a functional snapping claw that we observe in this study suggests that this particular function is of significant importance to snapping shrimp behavior and survival.
 
Mass-specific oxygen consumption rates (μg O 2 dw −1 h −1 ) in males, non-ovigerous females and ovigerous females of the prawn M. amazonicum. Medians with different letters are significantly different.
Mass-specific ammonia excretion consumption rates (μg mg dw −1 h −1 ) in males, nonovigerous-female and ovigerous females of the prawn M. amazonicum. Medians with different letters are significantly different.
Energy content of the entire body and feces of the prawn M. amazonicum.
The aim of this study was to evaluate differences in various physiological measures (growth, fecal production, feed intake, nitrogenous excretion, oxygen consumption, energy substrate used, and energy budget) among males, ovigerous females and non-ovigerous females of the freshwater prawn Macrobrachium amazonicum. This species exhibits pronounced sexual dimorphism and different male morphotypes and has the potential for use in aquaculture. Males and non-ovigerous females were studied for 30 days. Ovigerous females were studied for 10 days. Prawns were fed commercial prawn food, and all males were of the Translucent Claw (TC) morphotype. The results demonstrate physiological differences both between males and females and between females of different reproductive stages. Males had higher rates of ingestion, growth and oxygen consumption and less fecal loss than females. We postulate that in the absence of other morphotypes, TC males may exhibit increased growth rates. Males and females used protein as an energy substrate. Males channeled approximately 9% of their energy budget into growth, whereas non-ovigerous and ovigerous females channeled only 1.4 ± 0.4 and 0.07 ± 0.07%, respectively. Whereas males and non-ovigerous females channeled 9.0 ± 9.74 and 61.8 ± 3.0%, respectively, of the energy ingested into metabolism, ovigerous females channeled 97.7 ± 4.7% into metabolism, likely due to the frequent beating of their pleopods, which oxygenates and cleans the eggs. As reported for marine prawns, males and non-ovigerous females of M. amazonicum lost approximately 5% of their ingested energy in exuviae. The physiological differences observed between the sexes and between females of different reproductive stages might reflect corresponding differences in patterns of activity, growth, and reproduction.
 
(Colour online) Time-dependent changes in oxygen concentration in chambers in which copepods and Euphausia crystallorophias were respiring.
(Continued).
Surface seawater temperature (Temp), salinity (Sal), chlorophyll a concentration (Chl a), sea ice extent and species collected at each sampling sites in the Amundsen Sea.
The individual respiration rates of five biomass-dominant copepods (Calanoides acutus, Rhincalanus gigas, Metridia gerlachei, Calanus propinquus and Paraeuchaeta antarctica), and Euphausia crystallorophias furcilia, from the Amundsen Sea, West Antarctica, were determined using a Clark-type oxygen microsensor affording high temporal resolution. Measurements were conducted on specimens collected from waters exhibiting a very narrow temperature range (−1.68 to −1.32 °C), at sites located between 71 and 75°S, during the summer (31 January–20 March 2012). A short incubation time (3 h) was sufficient to reveal significant declines in dissolved oxygen concentrations by 12–45%. The respiration rates of the copepods and E. crystallorophias furcilia were within the ranges of previously reported values. The respiration rates of relatively large-bodied species were rather low, whereas the smaller species generally exhibited higher respiration rates. The data show that this simple microsensor technique is a useful high-resolution non-invasive means of investigating the metabolism of zooplankton in the Southern Ocean. The method could be used in other situations when such information is required.
 
(Colour online) Video frame captures of the Avocettina eel observed from the Shinkai 6500 submersible (JAMSTEC) on 17 July 2012 at a depth of 799 m showing ((a)–(c)) its vertical body position at three distances and ((d) and (e)) close-up views of the anterior body and head showing the elongated jaws.  
Drawings of specimens of the three genera of eels of the family Nemichthyidae showing (a) a 400 mm female A. infans, (b) a 580 mm female L. yanoi with a shrimp in its stomach and (c) a 680 mm female N. scolopaceus. Scale bars show 2 mm. Arrows show the position of the anal n origin and the anus. Adapted from Nielsen and Smith (1978).  
A nemichthyid eel apparently of the genus Avocettina was observed and video recorded during the day from a submersible operating above the deep western slope of the West Mariana Ridge at a depth of about 800 m. The eel was oriented vertically, head-upward, with its long-thin body held rigidly straight. It remained motionless for more than 1 min except for small constant oscillations of the tip of the tail. It showed no reaction to the presence of the approaching submersible until contacting it. This body position has been seen in nemichthyid eels previously by submersibles in the Atlantic, Pacific and Indian oceans. It is postulated to be a prey or predator detection tactic that optimizes the use of the visual or lateral line senses. It may also be an efficient way to maintain a position or to move slowly through the water column without disrupting sensory function.
 
Fig  
Escape behaviour was investigated in Queen scallops (Aequipecten opercularis) acclimated to 5, 10 or 15 degrees C and tested at their acclimation temperature. Scallops are active molluscs, able to escape from predators by jet-propelled swimming using a striated muscle working in opposition to an elastic hinge ligament. The first cycle of the escape response was recorded using high-speed video ( 250 Hz) and whole-animal velocity and acceleration determined. Muscle shortening velocity, force and power output were calculated using measurements of valve movement and jet area, and a simple biomechanical model. The average shortening speed of the adductor muscle had a Q(10) of 2.04, significantly reducing the duration of the jetting phase of the cycle with increased temperature. Muscle lengthening velocity and the overall duration of the clap cycle were changed little over the range 5 - 15 degrees C, as these parameters were controlled by the relatively temperature-insensitive, hinge ligament. Improvements in the average power output of the adductor muscle over the first clap cycle ( 222 vs. 139 W kg(-1) wet mass at 15 and 5 degrees C respectively) were not translated into proportional increases in overall swimming velocity, which was only 32% higher at 15 degrees C ( 0.37m s(-1)) than 5 degrees C (0.28 m s(-1)).
 
We studied the effect of the common ascidian Styela clava on the growth of small holothurians of the species Apostichopus japonicus (Selenka, 1867). In a traditional aquaculture system, the oxygen consumption rates, ammonia excretion rates, and ingestion rates of small A. japonicus were reduced significantly, which suggested that this group was stressed by the presence of large A. japonicus, and that this stress grew stronger with time. Oxygen consumption rates, ammonia excretion rates, and ingestion rates of small A. japonicus in an integrated aquaculture (IA) system with S. clava, microalgae, and A. japonicus were higher than those observed in the traditional culture system. Metabolic and digestive enzymes were more active in small A. japonicus in the IA system than in those in the traditional aquaculture system. These results suggest that the IA model did not affect the growth of large A. japonicas, but produced a marked positive impact on the growth of small individuals.
 
Variation in larval quality has been shown to strongly affect the post-metamorphic performance of a wide range of marine invertebrate species. Extending the larval period of non-feeding larvae strongly affects post-metamorphic survival and growth in a range of species. These 'carry-over' effects are assumed to be due to changes in larval energetic reserves but direct tests are surprisingly rare. Here, we examine the energetic costs ( relative to the costs of metamorphosis) of extending the larval period of the colonial ascidian Diplosoma listerianum. We also manipulated larval activity levels and compared the energy consumption rates of swimming larvae and inactive larvae. Larval swimming was, energetically, very costly relative to either metamorphosis or merely extending the larval period. At least 25% of the larval energetic reserves are available for larval swimming but metamorphosis was relatively inexpensive in this species and larval reserves can be used for post-metamorphic growth. The carry-over effects previously observed in this species appear to be nutritionally mediated and even short (< 3 h) periods of larval swimming can significantly deplete larval energy reserves.
 
Ambient sea noise and the noise generated by a small wooden trawler were recorded in Passamaquoddy Bay in summer and in winter. The recordings were analysed in “real‐time” in third‐octave bands. The measurements were combined with published data on masking effects on hearing of cod to calculate a minimum range at which cod can first detect trawling noise. The range is 10,500 ft (3.2 km) in summer, and 8,200 ft (2.5 km) in winter.
 
Frequency of food items ingested, rejected and disregarded for a) small and b) large gilthead sea bream.
The mean total handling time (seconds) ±SE taken to consume the food items for large and small gilthead sea bream.
Descriptions for food items fed to small and large sea bream with mean dimensions (mm) ±SE (N=48 for small sea bream food items and N=30 for large sea bream food items). L = length, D = diameter, W = width, H = height.
Many fish species have evolved feeding mechanisms and behaviours enabling them to feed on specific prey. However, such mechanisms may not be optimal for feeding on commercial-pelleted diets in aquaculture. Gilthead sea bream chew and occasionally eject pellets or parts of pellets from the mouth when feeding on commercial diets. This may result in an increase in nutritional waste from the intensive culture of this species. In this study we examined the prevalence of this food processing behaviour in two sizes of sea bream, feeding on three types of natural prey items in comparison to a commercial pellet, to give an insight into the circumstances in which excess chewing and ejection of food items from the mouth occurred. These included two hard-textured food items (commercial pellet and hard-shelled prey) and two soft-textured food items (larvae and small crustacean). Both sizes of sea bream frequently consumed the soft-textured food types, however large sea bream also frequently consumed hard-textured pellets. Hard-textured food required longer handling times and elicited more chewing and the ejection of food items from the mouth. These results suggest that future investigations on the food processing behaviour and consequent waste when fed commercial diets differing in texture could give an insight into improving diets and feeding efficiency for intensively cultivated gilthead sea bream.
 
Numbers of familiar and unfamiliar pellets eaten by individual control and experimental goldfish.
Numbers of familiar and unfamiliar pellets eaten by control and experimental goldfish in shoals of two.
Numbers of familiar and unfamiliar pellets eaten by control and experimental goldfish in shoals of three.
Numbers of familiar and unfamiliar pellets eaten by control and experimental goldfish in shoals of five.
To examine the effect of novelty in food selection by fishes, goldfish were trained by feeding them on red or green food pellets. Individual fish and fish in shoals of two, three, and five were then given a choice between equal numbers of familiar pellets and novel (yellow) pellets. In experimental groups, the yellow pellets were soaked in 15% quinine hydrochloride to make them unpalatable. Fish were next presented with equal numbers of familiar and a second novel pellet. It was expected that fish would generalize from their experience with the unpalatable pellets and demonstrate avoidance to sampling a second novel food item. However, as groups, neither controls nor experimentals were reluctant to sample the second novel pellets. Also, fish did not eat significantly more familiar than novel pellets when both were palatable. A third set of experiments examined food preference transitivity in which each pellet type was presented alone and in three pair-wise combinations to individual fish. Although red and yellow pellets were preferred over green, they were preferred equally, indicating an absence of transitivity in pellet choice and, perhaps, a “preference” for a mixture of red and yellow pellets.
 
To reference the 10 legs of a decapod, the animal's front right walking leg is leg number one; count clockwise and the animals front left walking leg is number 10. The chelipeds (or claws, used for food manipulation and competition) are legs 1 and 10 and the small hind legs (to aid in climbing) are legs 5 and 6. Legs 2-4 and 7-9 are the primary walking legs; grapsid crabs such as H. nudus walk with an alternating tripod gait (legs 2, 4, 8 followed by legs 3, 7, 9). Image by Masis Isikbay.
Patterns of regeneration for types of legs in a sample of 182 crabs. For males, there were a total of 145 regenerated legs (n claws = 11, n walking = 101, n back = 33). For females, there were a total of 181 regenerated legs (n claws = 11, n walking = 134, n back = 36). Values for both males and females are shown as a percentage out of the total legs regenerated. Dashed line represents expected values if rates of regeneration were 20% claws, 60% walking legs, and 20% back legs, and circles represent the expected rates of regeneration if animals regrow legs at a frequency relatively equal to their rate of autotomy.
Overall rates of individual leg injury (incidences of autotomy and regeneration combined) in a random sample of 272 crabs. For males, there were a total of 108 injured legs (n leg1 = 9, n leg2 = 5, n leg3 = 15, n leg4 = 10, n leg5 = 5, n leg6 = 11, n leg7 = 15, n leg8 = 19, n leg9 = 10, n leg10 = 9). For females, there were a total of 201 injured legs (n leg1 = 4, n leg2 = 19, n leg3 = 35, n leg4 = 29, n leg5 = 18, n leg6 = 19, n leg7 = 23, n leg8 = 24, n leg9 = 21, n leg10 = 9). If all 10 legs were injured at equal frequencies, we would expect each leg to equal 10% (dashed line). There were no significant differences between the observed and expected percentages for males, but females injured leg 1 less than expected and leg 3 more than expected.  
Leg autotomy and regeneration can have severe impacts on survival and reproduction, and these impacts may be even more pronounced in animals with multifarious legs, such as decapods. Thus, determining the patterns and frequency of autotomy and regeneration could reveal the effects of these processes on the individual and population level. We investigated whether some legs are lost more often than others and if all legs are equally likely to be regenerated. We sampled nearly 500 purple shore crabs (Hemigrapsus nudus) and showed that (1) most animals are found with at least one injured leg, (2) the patterns of autotomy differ between males and females, and (3) successful claw regeneration is unlikely in both males and females. Future work with H. nudus and other grapsid crabs will elucidate how patterns seen here relate to other developmental and ecological factors.
 
Denaturing gradient gel electrophoresis (DGGE) was used to study the bacterial community changes in the intestine of the sea urchin Strongylocentrotus intermedius during the digestion of Macrocystis pyrifera. The distinct bands in DGGE gels were sequenced, and the results indicated that the bacterial community in the large and small intestine varied at different periods of digestion. Samples from the large intestine included six specific bands belonging to the genus Psychromonas, whereas samples from the small intestine included eight specific bands representing Psychromonas, Shewanella, Saccharophagus degradans, and Nitrosomonas eutropha. The bacterial flora differed at different periods of digestion. The increase in the microbial community species in the large intestine was not obvious compared with that in the small intestinal microbial community. Several microbes involved in degradation of M. pyrifera were found in the intestine of sea urchin.
 
Survival rates of the rainbow trout (*) and brown trout (□) juveniles during a longterm starvation period. Notes: D22C: day 22 control, D22S: day 22 starved, D45C: day 45 control, D45S: day 45 starved.
Effects of starvation on growth parameters in rainbow trout and brown trout juveniles at low water temperature.
Hepatosomatic index values of the rainbow trout (□) and brown trout ( ) juveniles during a long-term starvation period. Notes: D22C: day 22 control, D22S: day 22 starved, D45C: day 45 control, D45S: day 45 starved.
MDA levels in the livers of rainbow trout (□) and brown trout ( ) juveniles after a 45-day starvation period. Notes: D0C: day 0 control, D22C: day 22 control, D22S: day 22 starved, D45C: day 45 control, D45S: day 45 starved. Different letters on the columns indicate statistically different groups (p < 0.05).
MDA levels in the muscle of rainbow trout (□) and brown trout ( ) juveniles after a 45-day starvation period. Notes: D0C: day 0 control, D22C: day 22 control, D22S: day 22 starved, D45C: day 45 control, D45S: day 45 starved. Different letters on the columns indicate statistically different groups (p < 0.05).
Biometric parameters and oxidative stress indicators were measured in liver and muscle samples from rainbow trout and brown trout juveniles exposed to a 45-day starvation period at low water temperature. As a general tendency, hepatic antioxidant enzyme activities in both species increased with fasting to eliminate the harmful effects of reactive oxygen species (ROS). However, the metabolic response to food deprivation in the muscle of each species was different. Lipid peroxidation levels in both species increased with starvation. We concluded that (1) low water temperature enhances ROS production in salmonids because of increased polyunsaturated fatty acid content in the cell membrane; (2) starvation significantly impaired the growth parameters of brown trout, yet the reverse was found for rainbow trout; and (3) despite this negative interaction, brown trout juveniles can physiologically tolerate oxidative stress caused by starvation and can therefore be cultivated under stressful conditions even in their early life stages.
 
The green shore crab, Carcinus maenas, undergoes on average 6 h periods of emersion during each low-tide cycle during the summer months. Under those conditions, the crab is cut off from its normal water environment and is exposed to potential stress from a suite of environmental and physiological changes: dehydration, compromised gas exchange and resultant internal hypoxia and hypercapnia, thermal stress, and ammonia toxicity. This study examined the comprehensive responses of the green crab in water and to a 6 h emersion period laboratory simulation of a tidal cycle followed by a 1 h re-immersion period, measuring indicators of dehydration, hemolymph osmolality, oxygen uptake, hemolymph acid–base status, heart and ventilatory rate, and hemolymph ammonia and ammonia excretion. Green crabs showed physiological responses of varying magnitude to 6 h of emersion. Individuals were found in the field exclusively under rocks and large clumps of seaweed where temperatures were approximately half those of exposed surfaces and relative humidity was about twice as high as ambient air. During emersion, crabs lost less than 5% of their wet weight, and hemolymph osmolality did not increase significantly. Oxygen uptake continued in air at about 50% of the control, aquatic values; and the gills continued to be ventilated by the scaphognathite, albeit at lower rates. Hemolymph lactate concentrations increased, indicating a shift to a greater reliance on anaerobic metabolism to support energetic needs. A slight acidosis developed in the hemolymph after 1 h of emersion, but it did not increase thereafter. Ammonia concentrations in the hemolymph were unchanged, as ammonia was volatilized by the gills and excreted into the air as NH3 gas. These results show that the green crab copes with emersion by seeking refuge in microhabitats that mitigate the changes in the physical parameters of intertidal emersion. Physiologically, desiccation is avoided, cardio-respiratory processes are maintained at reduced levels, and hemolymph acid–base balance is minimally affected. Ammonia toxicity appears to be avoided by a shift to excreting NH3 gas directly or indirectly to air.
 
This study evaluated the biological effects of high stocking density on mullet (Mugil cephalus). Fifty fish, caught from Faro lake, were divided into two groups, a low-density control group (n = 15), stocked at 3.4 kg/m3 in an 800 l tank and a high-density experimental group (n = 35), stocked at 8.4 kg/m3 an 800 l tank. The ammonia concentration in the control group tank reached 0.3 mg/l after 2 days while that in the experimental tank reached 5 mg/l. Haematological parameters and serum protein profiles were determined following blood sampling. An Unpaired T-test showed significant differences between the two groups on Red Blood Cell Count, Haematocrit, Haemoglobin, White Blood Cell Count, Mean Corpuscular Haemoglobin, Mean Corpuscular Haemoglobin Concentration, total proteins, albumin and α-globulins. In the experimental group, the disappearance of prealbumin and the γ-globulin fraction was particularly evident. Histopathological changes indicated that mucosal electrolytic failure was the main function compromised. This could eventually lead to death. The findings suggest that mullet is sensitive to stocking density linked to ammonia toxicosis.
 
Plasma cortisol concentrations in farmed rainbow trout (Oncorhynchus mykiss) were used to determine the stress caused by feeding, counting, grading and harvesting. The effect of carrying out these practices with the addition of an aerator was also determined. The cortisol concentration in trout plasma was assessed using enzyme immunoassay (EIA). Pre-feeding levels were found to be 3-4 ng/ml. Feeding, counting, grading and harvesting produced significant elevations in plasma cortisol. The presence of an aerator during these practices significantly reduced this cortisol response. The plasma cortisol response during winter grading was significantly less (p<0.0001) compared to Summer grading. Grading was also found to be a more stressful practice than feeding or counting. The cortisol response to grading was dependent on fish size (p=0.0027). Winter harvesting was more stressful than summer harvesting (p=0.0134), suggesting that lower temperatures may prolong the loss of consciousness. This study suggests that stress incurred by the trout during fish farming practices can be significantly reduced by oxygenating the water.
 
The effects of hypothermal (22–16 °C) and hyperthermal (22–28 °C) stress on the immune system responses of the shrimp Litopenaeus vannamei cultured in either freshwater or seawater were measured and compared. The following immune system indicators were measured for comparison: total hemocyte count (THC), activity of phenoloxidase (PO), nitric oxide synthase (NOS), superoxidase (SOD), and malondialdehyde (MDA) content. Thermal stress significantly decreased THC in both freshwater and seawater shrimp within 6–12 h (P 0.05). After hypothermal stress, all shrimp had a significantly lower THC level than their prechallenge levels (P 0.05). Under both types of thermal stress, the activity of PO, NOS, and SOD first increased and then decreased. After 48 h of thermal stress, shrimp PO and NOS activity decreased in both freshwater and seawater. After 48 h of thermal stress, the reduction in the SOD activity in the hemolymph of freshwater shrimp was greater than that in seawater shrimp. During exposure to stress, the MDA content in freshwater shrimp was significantly higher than in seawater shrimp, which demonstrated that lipids in freshwater shrimp were more susceptible to peroxidation than those in seawater shrimp, particularly at low temperatures. Large temperature fluctuations, particularly sudden cooling, should be avoided when rearing L. vannamei because of high rates of lipid peroxidation and decreased immunity. These effects are more marked in freshwater than in seawater.
 
Although the temporal consistency of resting metabolic rate in individual animals is generally considered to be a universal phenomenon, studies on invertebrates are still scarce. Here, we studied the repeatability of standard metabolic rate in the signal crayfish (Pacifastacus leniusculus). We measured oxygen consumption twice on the same individuals, on average in 97-day intervals. At intermolt stage, the standard metabolic rate was a repeatable trait. However, molting increased significantly the minimum metabolic rate, thus emphasizing the role of animal physiological state in determining the rate of metabolism.
 
Forty post-larval giant freshwater prawns (Macrobrachium rosenbergii) were weighed, measured, marked and placed in groups of 4. Social interactions were screened daily, moults were recorded and the nature and stability of dominance interactions characterised. Half of the prawns were screened for resting oxygen consumption before group formation. In most groups, one or two individuals ('dominants') consistently won the majority of interactions in which they were involved, while others ('subordinates') consistently lost; the remainder were classified as of intermediate social status. Prawns lost more fights on the day before a moult, but despite this, rank was retained after moults. Neither initial size nor growth rates varied with status, but prawns that became dominant had significantly higher resting metabolic rates before group formation than those that became subordinate. Thus in M. rosenbergii the outcome of aggressive interactions can be predicted from the metabolic physiology of the animals although whether the relationship is causal remains to be determined.
 
The aim of the investigation was a comparison of osmoregulatory ability at different water temperatures and salinities by the stenothermic isopod Saduria entomon (Linnaeus, 1758) and the eurythermic amphipod Corophium volutator (Pallas, 1766) from the Baltic Sea. The experiments were performed under laboratory conditions at different water temperatures (5, 10 and 15 °C) and salinities (3, 6.6, 15 and 25 PSU for S. entomon and 3, 6.3, 15 and 25 PSU for C. volutator). The osmotic concentrations of the crustaceans’ haemolymph were determined using the melting point method. Temperature had a statistically significant effect on the osmoregulation in S. entomon, but had generally no statistical influence on the osmoregulation in C. volutator. This physiological information regarding adaptation provides a basis for predicting the distribution of these species in changing environments. The implications of the results for the comparative adaptability of the two species are considered.
 
The oxygen production and consumption interaction between sand dollar's activities and microphytobenthic production response. Note: Panels (a) and (b), (c) and (d) are from experiments in March 2009 at different temperatures of 16 and 23 °C, respectively. Positive values indicate efflux of materials out of the sediment; negative values indicate influx into sediment. Before, experimental treatment and recovery are the three periods of each 4 h set up in sequence. In Before period, without animals; in experimental treatment, four individuals introduced and four controls; in recovery period, four individuals removed, without animals again. Error bars show the standard deviations for measurements that we made in duplicate chambers. With animals-treatment groups; without animals-control groups. 
Sand dollar P. lesueuri effect on nitrate fluxes. Note: Panels (a) and (b), (c) and (d) are from experiments in March 2009 at different temperatures of 16 and 23 °C, respectively. 
Sand dollar P. lesueuri effect on phosphate fluxes. Note: Panels (a) and (b), (c) and (d) are from experiments in March 2009 at different temperatures of 16 and 23 °C, respectively. 
Results of Chlorophyll a and Phaeopigments in sediment at the end of experiment (23 & 16 °C). Note: Panels (a)-(h) are the results of Chlorophyll a from experiments in March 2009 at different temperatures of 16 and 23 °C; panels (i)-(p) are the results of Phaeopigments from experiments at different temperatures of 16 and 23 °C, respectively. Error bars show the standard deviations for measurements that we made in duplicate chambers. With animals-treatment groups; without animals-control groups. 
Respiration and excretion rates of a key bioturbating species, the sand dollar Peronella lesueuri, were measured in mesocosms at three different temperatures. Benthic oxygen and nutrient fluxes were additionally measured at winter and summer temperatures to assess the impact of P. lesueuri on ecosystem processes. Oxygen consumption by sand dollars increased significantly with wet weight at all three temperatures 16, 19, and 23 °C. Ammonia release also increased with body weight. The weight vs. oxygen uptake relationship was similar at 19 and 23 °C but oxygen uptake was significantly reduced at the lower exposure temperature. The bioturbation caused by sand dollar P. lesueuri reduced the photosynthetic rate of the microphytobenthos (MPBs) but had a much smaller and less obvious effect on nutrient fluxes across the sediment–water interface.
 
This study reports on the molecular characterization and gene expression of Na+-K+-2Cl− cotransporter2 (NKCC2) in the gastrointestinal tract of Olive flounder Paralichythys olivaceus infected with Streptococcus parauberis. It examines the electroneutral cation-Cl− cotransporter, and NKCC2 expressed in the intestinal tract. First, we isolated cDNA encoding NKCC2 from the intestinal tract of Olive flounder and investigated the tissue distribution pattern of NKCC2 mRNA. Reverse transcription-PCR analysis detected expressions of NKCC2 in the intestine and kidney. A quantitative PCR analysis showed that the expression level of NKCC2 in the anterior and posterior intestines was higher than in the rectum. Second, we performed a challenge experiment comparing physiological saline (PS) and PS plus the bacteria and analyzed the subsequent gene expression of NKCC2. At 4 days after bacterial injection the comparison between treatment and control found that the expression levels of NKCC2 mRNA increased significantly in the posterior intestine of infected fish but not in the other segments. We discuss the suggestion that bacterial injection may disturb the ion uptake that provides the driving force for water absorption through parts of the intestinal wall.
 
The proportion of time greenlip abalone (H. laevigata) exhibited each behaviour over a 24-h period when fed an excess feed ration (1a) or a restricted feed ration (1b) of the experimental flake diet (Means; n = 3 replicate observations of 10 min at every 30 min interval over three consecutive 24 h periods). Feed introduced to the system at 1600 h, lights off (dashed line) at 1900 h, lights on (dotted line) again at 0700 h the following day and uneaten feed collected and aquaria cleaned at 0840 h the following day.  
Experimental treatment combinations used to assess the feeding behaviour of greenlip abalone (H. laevigata). 
The proportion of time greenlip abalone (H. laevigata) exhibited each behaviour over a 24-h period when fed an excess feed ration (2a) or a restricted feed ration (2b) of the commercial diet (Means; n = 3 replicate observations of 10 min at every 30 min interval over three consecutive 24 h periods). Feed introduced to the system at 1600 h, lights off (dashed line) at 1900 h, lights on (dotted line) again at 0700 h the following day and uneaten feed collected and aquaria cleaned at 0840 h the following day.  
The proportion of time greenlip abalone (H. laevigata) exhibited each behaviour over a 24-h period when fed an excess feed ration (3a) or a restricted feed ration (3b) of Ulva sp. (Means; n = 3 replicate observations of 10 min at every 30 min interval over three consecutive 24 h periods). Feed introduced to the system at 1600 h, lights off (dashed line) at 1900 h, lights on (dotted line) again at 0700 h the following day and uneaten feed collected and aquaria cleaned at 0840 h the following day.  
Abalone farmed in Australia are predominantly fed formulated feeds, while in the wild, their diet consists of a mix of macroalgae. Here we investigated the feeding behaviour of juvenile greenlip abalone, Haliotis laevigata; fed live macroalgae and formulated diets at different rations; and observed their feeding behaviour using a novel ventral video monitoring technique. Four different diets (commercial chip, experimental flake, Ulva sp. and Gracilaria cliftonii) at two feeding rations (excess vs. restricted) were tested. Diet type had no effect on abalone movement, but macroalgal diets resulted in higher feed intakes. Restricting feed rations induced greater movement. Abalone moved little during the light period and moved mostly during darkness, except for animals on the restricted feed ration where feeding commenced during the light period. On farms, this phenomenon may be a useful behavioural indicator for identifying underfed abalone. Despite their lower intake, formulated diets promoted higher energy and nutritional intake, indicating that quantity of feed consumed is not solely indicative of nutritional gain. From a research perspective, the novel ventral monitoring method has created opportunities for further behavioural studies in molluscs.
 
Results of the two-way ANOVA for shelled gastropod data, including retrospective power, for complexity, deployment time, and their interaction. 
Habitat parameters for the structures. Ct is the area of an individual ribbon multiplied by the total number of ribbons. Ct also includes the cross-sectional area of the three pvc pipes. At is the area of the base of the artificial structure. Sp is the average interstructural space size. 
Faunal abundances in spring and fall deployments, demonstrating that most fauna had significant differences in abundance between the two deployment times. Mean values and stan- dard deviations from all of the artificial structures deployed during that time are shown. p values are from two-way ANOVAs. 
Results of the two-way ANOVA for square root-transformed shrimp data, including retrospective power, for complexity, deployment time, and their interaction. 
We tested whether total cover and interstructural space size affect the abundances of mobile fauna colonizing small artificial structures deployed in a seagrass bed near Dubai, UAE, during May and September 2011. There were three complexity treatments: low cover with wide interstructural space sizes, high cover with wide space sizes, and high cover with narrow space sizes. This is the first study to deploy structures that vary interstructural space size while keeping cover constant and that vary cover while keeping interstructural space size constant. Shrimp had significantly higher abundance in the high cover/narrow space treatment compared with the low cover/wide space treatment. Complexity did not affect the abundances of most fauna. There were differences in the abundances of nudibranchs, amphipods, cumaceans, fish, shrimp, isopods, and crabs between the two deployment times. This is the first study demonstrating possible seasonal differences in UAE seagrass fauna.
 
Changes in plasma osmolality haematology, lipid content and fatty acid composition of the gills, intestine and kidney of the Thicklip Grey Mullet (Chelon labrosus) were investigated along a salinity gradient from seawater (SW, 38 p.p.t.) to low salinity water (LSW, 5 p.p.t.). Plasma osmolality has changed as evidenced by the dynamics of the osmoregulatory parameters. These dynamics have revealed two stages during hyperosmotic and hypo-osmotic acclimations: (i) an adaptive period during the first days of acclimation (3–7 days), with important changes in these parameters and (ii) a chronic regulatory period (after 3 days of transfer) where osmotic parameters reached hom0eostasis. From a metabolic point of view, we found that salinity decrease induced mobilization of lipids in the gills, kidney and intestine of C. labrosus. We also observed changes in fatty acid profiles but with differences between tissues. In gills and intestine, SFAs and MUFAs decreased and PUFAs increased in the first day of the transfer. However, in the kidney, PUFAs increased and SFAs and MUFAs decreased at the end of the transfer. We conclude that the changes made during salinity acclimation are followed by a qualitative variation in the lipids and that the decrease in salinity leads to an improvement in the synthesis of PUFAs fatty acid. This suggests that lipids are important in meeting the energetic demands resulting from exposure to salinity.
 
Relationship between the weight-specific swimming costs (g g À1 d À1 ) of Murray cod, body weight (g) and flow velocity (BL s À1 ).
(a–b) Mean daily flow velocity ( , BL s À1 ) and relative in the bottom 10% of the water column and temperature ( , °C) directly downstream of Hume Dam (River Murray) between July 2008 and June 2009.  
The influence of flow velocity and temperature directly downstream of Hume Dam (River Murray) on the swimming costs (g g À1 d À1 ) of juvenile Murray cod. For both figures, estimates are from the present study (net M A and ACT, ), Kitchell et al.'s (1983) fixed proportion method (net M A(K) and ACT K , ) and Stewart et al. (1983) the optimal swimming speed method (net M A(opt) and ACT opt , – – –.  
We develop a swimming costs model that accounts for the influence of flow velocity and body weight on the net active metabolic rate of Murray cod (Maccullochella peelii). Laboratory trials indicated that swimming costs increased with flow velocity (exponent = 2.36) and declined allometrically with body weight (exponent = −0.27). The newly derived swimming costs model provided a more dynamic estimate of Murray cod energy consumption, which explained 74% of variation in the swimming costs. This new model was compared to traditional bioenergetics models (fixed proportion and optimal swimming speed) to determine swimming costs in a variable temperature (6.4–26.1 °C) and flow velocity (0.06–0.46 m s−1) regime downstream of a large hypolimnetic-releasing impoundment on a major Australian river. Incorporating species-specific swimming cost models, such as the one developed here, into bioenergetics modelling allows the exploration of the impact of flow velocity in lotic systems on the growth responses of freshwater fish.
 
This work investigated the effect of carbon dioxide-induced decreased water pH (8.1 – control, 7.5 and 7.0), oxygen saturation (~100% and ~20%) and the combination of both factors on the behaviour (gaping activity) and the total metabolic rate of blue mussel Mytilus edulis trossulus from the southern Baltic Sea. Heat dissipation measurements were carried out in a Calvet-type isothermal twin calorimeter equipped with a flow-through system. The resting metabolic rate was not significantly (p > 0.05) affected by pH or oxygen saturation. Neither was there significant (p > 0.05) effect of the interaction of both factors on this process. The high inter-individual variability in behaviour affected the value of maximal recorded activity and duration of activity peaks connected with shell gaping behaviour. In some mussels, they were short and appeared periodically, and other individuals were inactive or exhibited temporal activity terms of different duration. The lowered oxygen saturation significantly (p p > 0.05) of lowered pH on this parameter, which indicates that oxygen deficiency may affect the Baltic population of M. edulis trossulus more seriously than acidification.
 
Environmental alterations are accelerating worldwide and the rate of change in ocean chemistry is predicted to happen so rapidly that it is unclear how marine ecosystems will respond. It is hypothesized that the phenotypic plasticity or acclimation capacity of an individual provides a buffer against environmental change; however, this plasticity depends on the speed at which the change occurs. Ocean acidification studies have found direct and acute responses from organisms exposed to elevated CO2 levels. Now, the challenge lies in integrating acclimation into experimental design in short-term studies, requiring proper preconditioning setups. Here we experimentally show that different preconditioning approaches produce different physiological and behavioral responses in the intertidal isopod Paradella dianae. Isopods were impaired when immediately exposed to elevated CO2 levels relative to individuals that were gradually acclimated to high CO2 concentrations. Abruptly introducing organisms to severe changes in CO2 conditions can produce confounding effects of short-term stress with acclimated responses to long-term shifts in ocean chemistry. By exposing organisms to sudden changes in CO2 concentrations, we are forcing immediate physiological stress reactions that could be independent of exposure to specific CO2 levels. We discuss how integrating acclimation in experimental design can help provide more accurate predictions about the impact of ocean acidification on marine ecosystems.
 
The Mormyridae are a diverse group of African freshwater fishes all of which have sophisticated electrosensory systems and specialization of the inner ear for detecting sound pressure. Neurophysiological and behavioral studies have shown that these animals are very sensitive to sound. Four species are now known to produce sounds for social communication. Within the genus Pollimyrus, males of two species produce elaborate species-specific sonic displays during courtship. Electric signals emitted by females are the primary releaser for the male's sonic display. The auditory pathway from the ear to the mesencephalon includes four processing areas in the medulla, a lemniscal nucleus and a major processing center in the mesencephalon. Acoustic responses are transformed along this pathway and some neurons in the mesencephalon show specificity for complex features of communication sounds.
 
Groups of swimming crabs, Portunus trituberculatus, were subject to sharp decreases of water salinity from 30 to 25, 20 and 15 psu, respectively, under laboratory conditions to simulate events that could occur during culture. Their osmoregulation and heat shock proteins (Hsps) expression were analysed. After the salinity stress, hemolymph osmolality, osmotic enzymes (Na+/K+-ATPase and carbonic anhydrase) activities in gills and Hsps (Hsp70 and Hsp90) expression in gills and muscles were measured. Dramatic changes in all parameters (p p P. Trituberculatus but a salinity change of less than 10 psu is likely to be harmless for crab farming.
 
A significant variation in membrane fluidity, lipid composition, fatty acids profile and intra–extracellular ion concentrations of chloride cells was observed in the estuarine mud crab, Scylla serrata, when they were acclimated to 1 and 35 psu. About 60% decrease in K m and V max of Na+/K+-ATPase, Mg2+ ATPase and Ca2+ ATPase enzymes and 85% increase in the same was observed when the crabs were acclimated to 1 and 35 psu saline water, respectively. The changed membrane lipid bilayer composition and fluidity of the plasma membrane of chloride cell help in modulating activity of Na+/K+-ATPase and thus regulate the ionic composition of the cell during salinity adaptation.
 
Changes in body mass and water content (WC), lipids, and fatty acid (FA) composition of muscle were determined in European eels (Anguilla anguilla) in the ‘yellow’ stage (sexually immature). The animals were held in either freshwater (FW) or seawater (SW) and deprived of food for four weeks. During this period, body mass decreased steadily. This decrease was accompanied by reduced muscle WC and total lipid in both SW and FW. ‘Yellow’ eels appeared to use lipids in muscle to provide metabolic and osmoregulatory energy. However, they maintained relative constancy in the FA profiles, so that total FA, saturated, monounsaturated, and polyunsaturated FA, were similar between salinities during short-term starvation.
 
Haemocytic neoplasia of mussels (HE staining). A – single cells (arrows), B – multifocal form, C – diffuse form, D – a neoplastic cell with a large, lobed, hyperchromatic nucleus.  
The health status of cultured and wild Mediterranean mussels in the Slovene Sea has so far been unexplored. Initially, 1280 adult Mediterranean mussels (Mytilus galloprovincialis), 960 from a shellfish farm and 320 from natural beds, were collected over a one-year period. Water temperature, oxygenation and salinity were measured at each sampling. Mussels were measured and weighted to calculate the condition index and microscopically examined for the presence of haemocytic neoplasia. Haemocytic neoplasia was detected in 14 mussels (1.1%) with a higher prevalence in cultured mussels. Neoplastic cells singularly infiltrated the connective tissue, in small foci or diffusely. Necrosis and multifocal atrophy of digestive tubules were noticed in mussels with diffuse neoplasia, whereas severe haemocytic infiltration of connective tissue was seen in mussels with single neoplastic cells. Haemocytic neoplasia was more frequently observed in spring and autumn. The average condition index of mussels with haemocytic neoplasia was slightly higher than in healthy ones. This is the first report of haemocytic neoplasia in Mediterranean mussels in the Northern Adriatic Sea. The disease occurs only sporadically and to date no significant impact on the mussel population has been noted.
 
Top-cited authors
John Miller Lawrence
  • University of South Florida
James William Grant
  • Concordia University Montreal
Iain Wilkie
  • University of Glasgow
Marco Vannini
  • University of Florence
Angelo Bisazza
  • University of Padova