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The microvariant genotype of Ostreid herpesvirus 1 (OsHV-1 μVar) has severely disrupted oyster production in Europe, New Zealand, and Australia by causing repeated and seasonal outbreaks of mass mortality in Pacific oysters (Magallana gigas). The virus was first detected in Tasmania, Australia, in January 2016, and mortalities of up to 87% were reported (de Kantzow et al., 2017). This study surveyed 95% of Tasmanian oyster farmers in OsHV-1 infected growing areas one year following initial detection, and recorded mortalities and associated farm management strategies in the 2016/2017 season, compared with the initial outbreak and before OsHV-1 occurrence. The survey was comprised of 37 open- and closed-ended questions, with data collected on background information, mortalities, environmental, genetic, and husbandry information. Perceived business viability was overall strong (75%), with changes to farm management occurring on 88% of leases in response to the virus. Commercial oyster farming businesses ranked handling regimes and stocking densities as the most important husbandry factors for influencing mortalities. Water temperature was ranked as the most important environmental factor, with 60% of businesses considering mean water temperature of 18–

Atlantic salmon (Salmo salar) are migratory salmonids and high-end seafood, and are widely cultivated. Its growth and development process needs to experience from freshwater to seawater phases. Salinity, as a key environmental factor, affects metabolism of Atlantic salmon, which in turn greatly affects its volatile organic compound (VOC) content and taste. We used headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and electronic tongue techniques combined with multivariate statistical analysis to detect VOCs and determine changes in the overall taste of Atlantic salmon in five different growth stages (freshwater: 8 months old; seawater: 15, 18, 21, and 24 months old; M1, M2, M3, M4, and M5, respectively). In addition, the content of free amino acids (FAAs) that affect flavor was determined. The fingerprint of Atlantic salmon from HS-GC-IMS identified ten potential markers, including one and three biomarkers in the freshwater and seawater phases, respectively, and showed the potential markers in each growth stage. The electronic tongue effectively distinguished the overall taste of Atlantic salmon in the freshwater and seawater phases. The total FAA content in the freshwater phase was significantly lower than that in the seawater phase, and the umami FAA level in M3 was the highest. Therefore, flavor compounds can be used as potential markers for Atlantic salmon culturing in freshwater and seawater environments and for their different growth stages. Our research will provide reference data for further improving its aquaculture technology and studying the changes of physiological and biochemical indicators during migration of Atlantic salmon from freshwater to seawater.

Extreme weather events are increasing with global climate change and are of concern to aquaculture and fisheries scientists and producers. Temperature is a key environmental factor determining fish growth and metabolism. Hence, the following study was conducted to investigate the effect of extreme temperature events on the growth and hematological parameters of European seabass, Dicentrarchus labrax. Fish were exposed to 8 °C, 16 °C, 24 °C, 32 °C for 30 days mimicking temperature extreme events. Growth performance measured as final weight, weight gain, specific growth rate, survival rate, and temperature growth coefficient was significantly impaired (p

Fighting and cannibalism between crabs are key factors that restrict increases in production and economic benefits. Temperature is an important environmental factor that affects the agonistic behavior and physiological activities of crustaceans. To explore the response mechanism of energy metabolism associated with agonistic behavior, we quantified the agonistic behavior and the concentrations of glycogen and key metabolites of the swimming crab (Portunus trituberculatus) at different temperatures (16 °C, 24 °C and 32 °C). The main results revealed the following: (1) fighting intensity, fighting duration time, and the frequency of the agonistic behavioral performances tended to increase with the increase in temperature. The frequency of “move to” and “contact behavior” at 24 °C and 32 °C of winners was significantly higher than those of losers, while the frequency of “move away” at 16 °C, 24 °C and 32 °C of winners was significantly lower than that of losers. (2) Before fighting, the concentrations of glucose and lactate in the hemolymph increased with the increase in temperature, and the concentration of lactate was significantly higher in the 32 °C group than in the 16 °C group. After fighting, the concentration of glucose in the hemolymph tended to increase at first and then decrease with the increase in temperature. The glucose concentration was significantly higher in the 24 °C group than in the other groups. After fighting, the concentration of lactate tend to increase continuously with the increase in temperature, and the concentration was significantly higher in the 32 °C group than in the other groups. (3) After fighting, the glucose concentrations in the hemolymph in the 16 °C and 24 °C groups were significantly higher than before fighting, and the lactate concentrations in the 16 °C, 24 °C and 32 °C groups were significantly higher than before fighting. (4) The glycogen concentration in the claw muscle of winners in the 16 °C and 24 °C groups were significantly lower than those of the losers, while the glucose concentration in the hemolymph of winners in the 16 °C and 24 °C groups were significantly higher than those of the losers. The concentrations of pyruvate and citrate in the hemolymph of the winners in the 32 °C group were significantly higher than those of the losers. These preliminary results showed that temperature significantly affected the agonistic behavior and energy metabolism of the swimming crab, and that the agonistic behavior resulted in significant changes in key metabolites.

Mass mortality of ark clam, Scapharca broughtonii, occurred in a local farm along the Bohai Sea, China in August 2017. Ostreid herpesvirus SB strain, which was the only pathogen previously reported in S. broughtonii, was not detected in moribund S. broughtonii. However, four kinds of bacteria were isolated from the hepatopancreas of naturally diseased S. broughtonii, and they were further identified based on 16S rDNA gene sequence analysis. These bacteria were closely related to Vibrio harveyi (A2-1), Microbulbifer variabilis (A2-2), V. alginolyticus (A2-3), and Pseudoalteromonas sp. (A2-4). Hemolysis test showed that A2-1 exhibited a strong hemolytic activity. The cumulative mortality of S. broughtonii with foot-injected A2-1 reached 100%, which was significantly higher than that of groups infected with other bacteria. Notably, temperature showed a significant effect on the mortality of S. broughtonii infected with A2-1, as the immersion challenged test showed 100% mortality occurred at 25 ± 2 °C on the 9th day, whereas no death was observed at 15 ± 2 °C on the 12th day. Temperature also significantly affected the growth rate and extracellular protein secretion of A2-1. In conclusion, this study is the first to report that V. harveyi is a pathogen that causes mass mortality in S. broughtonii, and the temperature is an important environmental factor that affects the virulence of A2–1 on S. broughtonii.

Marine hypoxia owing to nutrient enrichment of water bodies by anthropogenic activities has become a global problem for several decades. Another marine environmental factor, salinity, plays an important role for marine organisms and fluctuates greatly in estuarine and coastal ecosystem, where hypoxia frequently occurs. The present study evaluated the interactive effects of hypoxia and salinity on immune functions of hemocytes in the green-lipped mussel Perna viridis , which widely distributes in estuarine and coastal waters of the Indo-Pacific region. Mussels were subjected to six combinations of oxygen levels (hypoxia: 1.5 mg O 2 l − 1 , normoxia: 6.0 mg O 2 l − 1 ) and salinities (15‰, 22‰ and 30‰) for 168 h. Mussel hemocytes were sampled after 24 h, 48 h, 96 h and 168 h exposure, for analysis of immune functions including hemocyte mortality, phagocytosis, esterase, reactive oxygen species (ROS) production, lysosomal content and total hemocyte counts using flow cytometric methods. Thereafter, all treatments were recovered to normoxic condition (6.0 mg O 2 l − 1 ) and salinity 30‰ for 24 h to study the recovery of immune functions from the combined hypoxic and hyposaline stresses. Interactive effects of dissolved oxygen (DO) and salinity on all immune parameters were observed during the experiment. Generally, hemocyte mortality was higher at low salinity than that at high salinity levels; higher hemocyte mortality was also noted when mussels were exposed to hypoxia compared with normoxia. Phagocytosis at low salinities and hypoxia was decreased compared to normal DO and salinity treatment, respectively. The activity of esterase and ROS production at low salinity and hypoxia were reduced, respectively. Lysosomal content and total hemocyte counts were lower at low salinity and hypoxia compared to other treatments, respectively. After 24 h recovery, hypoxia and salinity effects were still significant among previous treatments, indicating immune functions of P. viridis could not recover from combined stresses in a short time.

We investigated the effects of low-salinity water on the growth, survival, and activity of artificially reared Japanese eel larvae (Anguilla japonica), proceeding from the assumption that such water quality saves energy due to lower cost for osmoregulation. We reared 5-day-old larvae in 0%, 10%, 30%, 50%, 70%, and 100% seawater (SW) with or without diet for 13 days. All larvae reared in 0% and 10% SW died within 6 days, while larvae in 70% and 100% SW survived until 9 days. Larvae in 30% and 50% SW further survived until 13 days without diet. Significant growth in body depth was observed in 30% and 50% SW after 7 days rearing with diet (0.65 ± 0.02 and 0.62 ± 0.02 mm, respectively) as compared with the initial size (0.49 ± 0.03 mm), while no significant growth was observed under the other salinity conditions examined. Larvae swam actively in the light (about 2000 lx) in 50%, 70%, and 100% SW, while they were apparently inactive in 0%, 10%, and 30% SW. The long-term rearing trial showed a 2.2-fold higher 2-month cumulative survival rate in 50% SW (18.2%) than in 100% SW (8.2%). The body depth of larvae in 50% SW (1.58 ± 0.47 mm) was also significantly larger than in 100% SW (1.32 ± 0.35 mm). These findings indicate that the intermediate salinity can result in better growth and survival performance in Japanese eel larvae.

A long-term environmental study was conducted to evaluate the significance of water temperature, pH and salinity on the prevalence of Streptococcus iniae mortalities in barramundi sea-cage facilities. It was determined that there is a strong association between temperature and increased mortality, specifically between 25 and 28 °C. Temperatures outside of that range result in decreased mortalities attributed to S. iniae. There was no statistical significance between pH or salinity and S. iniae induced mortality (pN0.05), although acidic conditions (bpH 6) occurring due to anthropogenic disturbances did result in acute mortalities and S. iniae was recovered from approximately 70% these fish. Laboratory challenge studies confirmed the temperature dependence of S. iniae infections as well as the increased susceptibility of barramundi to S. iniae during acid water conditions.

International audience; Fractional factorial design is a practical approach for studying multiple factors, with a minimum of experimental units. The objective of this work was to study the simultaneous effects of nutritional and environmental factors on both growth and flesh quality of common perch (Perca fluviatilis), a new inland aquaculture species. This study sought answering the two following questions: (i) which combinations of factors allow improving growth, food efficiency, and technological, sensorial and nutritional qualities? (ii) is it possible to simultaneously improve growth performances and flesh quality? In a first experiment, twelve factors (7 nutritional and 5 environmental factors) were each tested at 2 levels in a fractional factorial design in 24 independent recirculating 500 L tanks. The best 4 combinations identified in this first experiment were then validated in a second experiment. The first phase of the multifactorial approach used here allowed revealing emergent information: i) there is a combination of factors that allows reducing both the heterogeneity of the production and the losses of nitrates and phosphates, while preserving good characteristics of growth and quality of fillets; ii) it is possible to improve the quality of the aquatic production system, without decreasing significantly growth efficiency; iii) the effect of a given factor, even such an important one like diet, temperature or target biomass, depends on the levels of the other rearing factor levels, thus the usual reference optimum used for a given factor has no meaning theoretically and can be questioned according to the levels of the other factors which act altogether on the functioning of the rearing system. The input factor combinations resulting in a significant enhancement of single output variables or several output variables were identified (e.g. improvement of feed efficiency, and/or fillet docosahexanoic acid content). Our results clearly demonstrate a strong interdependence of input factors into the animal rearing system, particularly between nutritional and environmental ones.

The diurnal feeding rhythms of cage-held Atlantic salmon parr were studied when fish were held for 205 days (September 2nd until 26th of March) under ambient daylength (8.42–15.25 h) and water temperature (4.5–15.25 °C) in commercial freshwater cages (576 m3: 12 m × 12 m × 4 m). The influence of environmental factors (daylength, change in daylength, water temperature, water clarity, daily rainfall and mean daily wind speed) on the variation in daily ration between days and seasons was also investigated. Three cages of fish (mean weight of 23.06 ± 1.29 g; n = 31351 ± 1115 fish group− 1) were stocked at an initial density of 1.26 ± 0.11 kg m− 3, reaching a max. density (prior to size grading in February) of 3.06 ± 0.18 kg m− 3 (mean ± SEM). Fish were given the opportunity to feed to daily satiation (from dawn until dusk) using appetite-based commercial on-demand feeding systems. Fish did not consume food throughout the whole day, and there was a general trend for daily feeding rhythms to change with season, from a morning peak in summer to a midday peak in winter. There was also some evidence of asynchrony in timing of feeding rhythm peaks between cages. Daily ration (% body weight day− 1) decreased during autumn and winter before increasing in spring. Stepwise multiple regressions analyses demonstrated that this decrease was significantly related to seasonal changes in temperature (all cages) and the directional change in daylength between days (two cages). R2 values accounted for 68.21%, 68.99% and 64.67% of the variability in daily ration for cages 1, 2 and 3 respectively.

Temperature is recognized to be the most important environmental factor affecting growth and protein synthesis in fish. The optimal temperature for growth of juvenile barramundi is 31 °C, although culture often occurs at temperatures which are above and below this optimum. Juveniles (2.96 ± 0.46 g) were held at five different temperatures ranging from 21 to 33 °C at 3 °C intervals. Fish were fed to satiation twice daily (504.5 g kg− 1 crude protein, 190.5 g kg− 1 lipid, 128.5 g kg− 1 ash, and 20.2 GE MJ kg− 1). Daily feed intake (g), growth (% d− 1), growth efficiency, and protein synthesis (measured 24 h after feeding) were determined for each temperature. Feed intake was significantly higher at 33 °C, than at any other temperature. Growth and growth efficiency were not significantly different between the 27, 30 and 33 °C groups but were significantly higher than the 21 and 24 °C groups. In order to take account of the variation in protein synthesis over the 24 h following feeding and model daily protein turnover, daily rates of protein synthesis were estimated from previously determined relationships between white muscle and whole body rates of protein synthesis. This showed that protein synthesis was not significantly different between 27 and 33 °C, synthesis retention efficiency was over 40% at these temperatures, and at 21 °C growth efficiency was poor. Growth efficiency and protein metabolism were optimal over a temperature from 27 to 33 °C.

10 páginas, 6 figuras., A major problem in the development of Senegalese sole Solea senegalensis intensive culture is the poor control on reproduction, in part due to the lack of knowledge on the precise role of photoperiod and temperature. Thus, gonadal maturation was evaluated by assessing the sequential changes in plasma levels of 17β-estradiol (E2), 11-ketotestosterone (11-KT), and testosterone (T) in both female and male cultured Senegalese sole (F1 generation) exposed to various combinations of constant or naturally-fluctuating daylength and water temperature. Under natural photoperiod (NP; 36° N), exposure to constant temperature (t0; 18–20 °C) disrupted gonadal development, as indicated by a lower incidence (in comparison with naturally-fluctuating water temperature; 14–24 °C) of females at advanced maturation (from February to April: 12 vs. 33%) and running males (from February to May: 46% vs. 57%), and the reduced mean (± S.E.M.) sex steroid plasma levels (female peak E2 levels: 2.9 ± 0.28 vs. 1.8 ± 0.3 ng ml− 1; male peak T levels: 1.5 ± 0.14 vs. 0.9 ± 0.06 ng ml− 1). Therefore, the onset and progression of gonadal development in this species seem to be strongly (“proximally”) influenced by fluctuating water temperature. When compared to NP and t0, exposure to continuous light (LL) under t0 significantly reduced steroid production (female peak E2 levels: 1.8 ± 0.28 vs. 0.5 ± 0.05 ng ml− 1; male peak 11-KT levels: 9.4 ± 1.06 vs. 5.4 ± 1.33 ng ml− 1) and subsequently gonadal development (lower proportions of females at intermediate [46 vs. 6%] and advanced maturation [12 vs. 0%] from February to April and of RM [46 vs. 33%] from February to May). Thus, the seasonal changes of daylength would be crucial for normal gonadal development, being its cueing effects of higher magnitude than those of water temperature. The present report constitutes the first systematic study focused on the environmental control of reproductive events in Senegalese sole., This research has been founded by the Spanish MCYT/MEC grant project AGL2000-0179-P4-02 to G. Martínez-Rodríguez, and by the CSIC fellowship (I3P programme, ESF) to A. García-López.

A series of experiments was conducted to evaluate the effects of diet, stocking density, and environmental factors on growth, survival, and metamorphosis of Manila clam Ruditapes philippinarum larvae. These experiments examined the following factors: diet (Isochrysts spp., Chlorella spp., and a mixture of Isochrysis spp. and Chlorella spp. [ 1: 1 w/w]), stocking density (5, 10, 15, and 20 larvae ml(-1)), light intensity (un-shaded, partially shaded, and fully shaded), water filtration (unfiltered and sand-filtered), water exchange (50% and 100% once every other day, 25%, 50%, and 100% once daily; 50% and 100% twice daily), and the use of substrate (with and without sand as the substrate). Results indicated that Chlorella spp. could replace 50% of Isochrysis spp. as a food source for the Manila clam larvae without affecting growth, survival, and metamorphosis. Larval growth decreased significantly with increasing stocking density. A density of 5-10 larvae ml(-1) appeared to be optimal for normal growth of Manila clam larvae. Neither diet nor stocking density used in the study had a significant effect on larval survival. Under partially shaded (light intensity = 1000-5000 lx) and fully shaded (light intensity

Temperature is recognized to be the most important environmental factor affecting growth in fish. Barramundi are cultured over a wide range of temperatures and extreme high temperatures which they can experience under culture approach the upper thermal tolerance limit for this species. A growth trial was conducted on juvenile barramundi to examine the effects of high temperatures ranging from the minimum optimal temperature (27 degrees C) for growth efficiency to the extreme upper thermal limits (39 degrees C) for feed intake, growth and growth efficiency. Juveniles (4.87 plus or minus 0.32 g) were held at four different temperatures 27, 33, 36 and 39 degrees C and fed twice daily to satiation (503.5 g kg-1 crude protein, 182.5 g kg-1 lipid, 150.1 g kg-1 ash, 20.52 GE MJ kg-1). Feed intake (g per day) and SGR (% per day) increased with increasing temperature up to 36 degrees C. At 39 degrees C feed intake, growth, feed efficiency ratio, protein efficiency ratio and productive energy value were significantly lower than at the other temperatures. This demonstrates that growth was optimized at temperatures from 27 to 36 degrees C and that barramundi have a much wider range for maximum growth efficiency than preciously thought.

Cultured gilthead sea bream (Sparus aurata L.) are exposed to a multifactorial disease termed “winter syndrome”, and low temperatures are the recurrent inducing factor. The effects of low temperatures on tissue composition and fatty acid profiles of polar and non-polar lipid fractions of sea bream were studied in two conditions: a gradual temperature drop (GD: from 18 °C to 8 °C at a rate of 1 °C·day− 1) or two sharp drops (SD: from 18 °C to 12 °C and then from 12 °C to 8 °C completed within a day, with a 1 week interval). No significant differences were detected between GD and SD in any of the variables studied. Animals stopped feeding when the temperature fell below 13 °C, and the resulting fast provoked body weight losses of 12% (GD) and 10% (SD) at the end of the experiment (15th day), and decreased non-polar lipids content in muscle. Unsaturation of polar fatty acids in muscle (SD) and in gills (SD and GD) rose, demonstrating a homeoviscous acclimation of membranes to cold. In contrast, unsaturation of liver polar fatty acids did not rise, but liver showed a great increase in total lipid content on day 15 (+ 35% SD, and + 43% GD), caused by the increase in non-polar lipids, especially n-3 fatty acids. The high deposition of these essential fatty acids, mainly 22:6n-3, in fasting sea bream implied mobilization from extra-hepatic stores and caused dramatic modifications in the physical properties of the liver (larger, more friable and yellowish), often associated with winter disease. Moreover, plasma aspartate aminotransferase (ASAT) levels rose three-fold in the two conditions. No fish succumbed to winter disease, but the incipient appearance of symptoms was evident. The relationships between the changes in muscle, gill, and, especially liver, at low temperature and the clinical signs of ‘winter disease’ are discussed.

Cold temperature decreases feed intake and growth of channel catfish, but the physiological and molecular mechanisms associated with the growth depression remain unknown. Therefore, an experiment was conducted to determine the effects of a 28-day exposure to cold temperature or feed deprivation at warm temperature on growth, physiological indices, and the expression of genes involved in muscle growth and metabolism. Juvenile channel catfish (initial mean weight 119.7 ± 8.0 g) were stocked into six 189-l tanks (20 fish per tank) with two replicate tanks for each of three treatments: Cold-fish reared at ≈ 10 °C and fed to excess once daily, Feed-Restricted-fish reared at ≈ 27 °C and deprived of food, and Control-fish reared at ≈ 27 °C and fed to excess once daily. Muscle and blood samples were collected on days 1, 14, and 28, and final body weight, organ weight, and fillet fat and moisture were collected on day 28. Plasma samples were analyzed for cortisol and creatine-kinase activity. Abundance of mRNAs encoding myostatin, myosin heavy chain (MHC), and heat shock protein-70 (HSP-70) in muscle was determined via real-time quantitative PCR. Final body weight, weight gain, specific growth rate, condition factor, and liposomatic index were highest in control fish, intermediate in cold treatment fish, and lowest in feed-deprived fish. Fillet fat was lower and fillet moisture was higher for feed-restricted fish than for cold and control fish. Cold treatment fish had a greater hepatosomatic index than either control or feed-deprived fish. On day 1 cold treatment fish had greater plasma cortisol concentrations than control fish. Creatine kinase activity was greater for cold and feed-deprived fish than for control fish on day 14. Myostatin mRNA abundance was lower for cold and feed-deprived treatment fish than for control fish on day 1. Myostatin and HSP-70 mRNA was increased on day 14 and day 28 in the cold treatment fish relative to the control or feed-deprived fish. MHC mRNA was increased in the cold treatment fish on day 14. Voluntary suppression of feed intake associated with cold water temperature and feed restriction at warm temperature both reduced growth in channel catfish, but patterns of gene expression in the two treatments were not similar.

The respiratory rates of Litopenaeus stylirostris were measured at three different salinities (20, 30, and 40) and temperatures (20, 30, and 35 8C). Equations of routine oxygen consumption (VO2) and weight-specific oxygen consumption (QO2) were obtained for the nine combinations and regression models for the effects of temperatures and salinities were derived from the data. Temperature,salinity,andcombinations ofsalinityandtemperature hadasignificant effect onoxygenconsumptionrate (pN0.05). The lowest values were found at a salinity of 30, suggesting that the iso-osmotic point may be at about this value. The thermal coefficient(Q10) did not vary withsalinity, but did vary withtemperature. Q10was 0.62 between 20 and308C, 2.5between 30and 35 8C, and 1.88 over the full temperature range. The partial coefficients and the multiple regression equation were highly significant suggesting that culture of this species would be optimum at salinities between 25–38 and temperatures of 20–30 8C. D 2004 Elsevier B.V. All rights reserved.

We aimed to identify the optimal salinity for the acclimation and early weaning of European glass eels and elvers using growth performance, survival indices and tissue morphology, as well as evaluate the effects of three different diets (hake roe, a semimoist compound diet and a dry pelleted commercial compound feed) on the nutritional condition and health of young fish. Glass eels (initial body weight: 0.165±0.15 g, mean±S.E.) were kept at (0‰, 5‰ and 15‰) and fed experimental diets over a 75-day period. At the end of the rearing period, significant differences were observed between fish fed the different diets and kept in 0‰, 5‰ and 15‰ environments. In all trials, a better growth performance, survival and nutritional condition was observed in those glass eels fed hake roe, independently of the salinity considered. Changes in the normal organization of the digestive system and musculature of glass eels were related to the diets, rather than the experimental salinities in which fish were kept. Glass eels fed hake roe showed the presence of a helmith (Digenea class) located in their abdominal cavity (prevalence of the parasite: 30%), although this parasitic infection did not represent an important source of mortality. Feeding fish with compound diets resulted in severe dietary-induced alterations of the digestive mucosa, liver and muscle organization. Atrophy of muscular fibers and lipid intermyofibrillar deposits, as well as, intestinal and hepatic steatosis were common features in fish fed both compound diets. Glass eels fed semimoist compound diet also showed focal invasions of cocci and bacilli in their stomach and intestine, respectively. Although fish roe might be an important vector for parasite transmission, up to date and due to the absence of a balanced compound diet specifically formulated for glass eels, this feed seems to be the most appropriate for feeding glass eels.

The dissolved oxygen level is an essential parameter for defining water quality in aquaculture. However, the optimal values of this gas can vary greatly depending on the species, body weight, or water temperature. In this study, different oxygen level categories (optimal, suboptimal, dangerous, and lethal) were established for Octopus vulgaris (0.18–2.20 kg; 15.5–27.4 °C) according to ventilatory frequency (Vf) and oxygen consumption (MO2) in response to gradually decreasing dissolved oxygen levels. Initial and maximum ventilatory frequency (Vf0 and Vfmax, respectively) and oxygen saturation at which ventilatory frequency is altered (SVf) showed mean values of 17.7±3.29 bts/min, 33.3±5.86 bts/min, and 62.8±15.94% (4.5±0.95 mgO2/l), respectively, and all variables were positively correlated with temperature (P

Successful in-sea aquaculture of sponges for metabolite production requires a sound understanding of the effects of environmental factors on explant growth, survival and metabolite biosynthesis. Using short-term experiments, we examined the effects of season, water flow and depth on the culture response of the New Zealand Demospongiae Latrunculia wellingtonensis (Alvarez, Bergquist and Battershill) and Polymastia croceus (Kelly–Borges and Bergquist). Sponge pieces were cultured seasonally for 2 months at depths of 5 and 10 m at three sites close to parent populations but characterised by differing water flow: high, medium and low. Survival of L. wellingtonensis and P. croceus was lowest in summer, possibly because of the relatively higher water temperature increasing stress during translocation. Growth of farmed sponges varied greatly among seasons, being greatest for L. wellingtonensis in winter and P. croceus in spring, and lowest for both species in autumn. Seasonal variation in growth may result from seasonal variation in food abundance and/or periodic investment of metabolic resources in reproduction. Within each season, growth of both species was greatest overall at the high-flow site, with increases up to 12.5% in weight per month. Culture depth influenced the final size of transplanted sponges by interacting with season and water flow. Bioactivity, a measure of metabolite biosynthesis, was high for both species regardless of the environmental condition.

Immunoglobulin M (IgM) in teleost fishes is the only component of the specific humoral defense system that is affected by environmental factors. In the present study, we examined the effect of various environmental factors (water temperature, salinity, pH and suspended solids) on the plasma IgM in the Nile tilapia, Oreochromis niloticus. For all treatments, fish were acclimatized in particular environmental conditions for 2 or 4 weeks. For fish reared at 18.4, 23 and 28 °C, the circulating IgM concentration increased with increased water temperature for 2 weeks. Rearing the fish at 33 °C resulted in a decrease in IgM concentration, suggesting that the fish possess an appropriate thermal range for production of immune substances. Plasma level of IgM increased significantly with salinity at 12 and 24 parts per thousand (ppt). On the other hand, plasma IgM concentration did not change by exposing the fish to acidification (pH 4.0) and suspended solids (20, 200, and 2000 mg/l). These results suggest that the specific immune system of tilapia changes by certain factors in aquatic environment.

Duplicates of a domesticated (H-line) and a naturalised line (S-line) of Oncorhynchus mykiss were examined for growth performance and tolerance to acute exposure to water temperature of 27 °C. After 516 days from hatch, fish from the H-line were, on average, 11% longer and 24% heavier than fish from the S-line. Fish from the H-line also displayed lower coefficients of variation in length and weight than fish from the S-line. H-line fish had a significantly greater tolerance to water temperature of 27 °C than S-line fish and significant logistic models were developed for each line. LT50's of H-line fish were approximately double the LT50's of S-line fish. Length or weight within a line was not significantly correlated with survival time at 27 °C. The results indicated that the H-line of O. mykiss is well adapted to the relatively hot summer conditions of Western Australia and that directed selection for faster growth has been effective in selecting for increasing heat tolerance within this line. The implications for establishing an even more heat-tolerant line of O. mykiss are discussed in relation to global warming.

An experiment was conducted to determine the effects of temperature and salinity on the growth and survival of the mud crab Scylla serrata, and the combined optima for these parameters during the nursery phase. Instar 2 crablets, mean weight 18.43±0.42 mg were individually reared at combinations of temperature (20, 25, 30, and 35 °C) and salinity (0‰, 5‰, 10‰, 20‰, 30‰, and 40‰) for 18 days. Crablets were fed an artificial penaeid diet to satiety each day and at harvest were weighed, and the carapace width was measured. All crablets held at 0‰, regardless of temperature, were dead the morning after stocking and were therefore excluded from any data analysis. Survival was significantly different among treatments due to temperature but not due to salinities between 5‰ and 40‰. The mean survival for the various temperatures were 36.0%, 98.0%, 96.0%, and 94.0% for temperatures of 20, 25, 30, and 35 °C, respectively. Growth, as measured by individual wet weight at harvest, carapace width, instar 3 intermoult duration, and weight-specific growth rate (WSGR percentage per day), was influenced more by temperature than by salinity, although both had significant effects on all parameters examined. Analyses indicate that maximum WSGR of around 16% day−1 was achieved at 30 °C and 10–20‰ salinity. Based on the findings of this experiment, S. serrata juveniles from the Northern Territory of Australia should be reared at approximately 30 °C with salinities in the range of 10–25‰ in order to achieve maximal production.

Using thermal induction, fertile tetraploids of Megalobrama amblycephala were generated. Survival of hatchlings, from eggs that were heat shocked at different time intervals post fertilization, showed that the eggs were sensitive at two different ages after fertilization and the first one was more suitable for thermal induction than the latter. A thermal shock at 40 °C for 2 min applied 33 min (τ0: 1.40) after fertilization to eggs resulted in the highest yield (6.3%) of tetraploids. At the age of 330 days, tetraploidy was confirmed in them by karyotyping and erythrocyte nuclear volume measurement by particle size analysis. Induction at the optimum thermal shock to 51-min (τ0: 2.17) old fertilized eggs led not only to poor yield (1.7%) but also to significantly higher frequency (32%) of abnormal juveniles. Male tetraploids attained sexual maturity at the age of 2+, when only 11.4% of the 4n females were matured. The remaining 71.4% of females matured at age of 3+. Hatching success of the cross 4n♀× 4n♂ was 60.8% with mean tetraploidy rate of 93.2% in the offspring.

Three color strains of the n-carrageenan producing red alga Kappaphycus alvarezii were cultured in Dzilam, Yucatan, over a 6-month period using the fixed off bottom monoline culture method to determine the technical viability of producing commercially this seaweed in the tropical waters of the Yucatan peninsula. Seawater temperature ranged from 28 to 31 8C, with a daily fluctuation range between 25.9 and 31.9 8C. Irradiance showed a strong fluctuation along the study period with maximal recorded irradiance during April (881.8 Amol photon m � 2 s � 1 ). Ammonia accounted for 55.1-89.8% of total DIN depending on the season, and salinity did not change significantly. Temperature was the only environmental factor that explained 96% of the observed variation in K. alvarezii growth rate (R 2 =0.96). The highest average growth rates obtained were 6.5F1% day � 1 for the red strain, 7.1F1.8% day � 1 for the brown strain, and 8.1F1.6% day � 1 for green strain during June. Lowest growth rates were obtained during August and September for the green strain (2.0F0.6% day � 1 ). Despite the significant differences in growth between months no significant differences among color strains were found (PN0.05). The growth rates of K. alvarezii were exponential during April to June. A 10-fold increase in weight was obtained after 30 days in cultivation for all the colored strains. As propagule weight increased the growth rate was reduced. Further, biomass yield (% weight gained) fluctuated as propagule weight increased and averaged 33.2F8.4% for the green, 35.4F6.0% for the red and 36.3F10.8% for the brown strain after 15 days. The highest carrageenan yield was obtained for the green strain (40.7%), whereas average carrageenan yields for the red strain were 32.7F3.9% and 37.5F1.1% for the brown. This study shows that K. alvarezii can be grown in the tropical waters of the

Cataracts leading to visual disturbance or blindness in farmed Atlantic salmon (Salmo salar L) in Northern Europe have been a common occurrence during the last years. The cause of cataracts in farmed salmon may be considered multifactorial, with both dietary factors as well as environmental factors involved in cataractogenesis. Deficiency of histidine or histidine-related compounds has been suspected of being a significant contributing factor. In this series of studies, the effect of feeding increased histidine concentrations, as well as feeding a diet with 5% NaCl added before and during smoltification on later cataract development was investigated. The influence of variation in water salinity and temperature on the effect of feed NaCl and histidine concentrations was further studied. In addition, the possible effect of feeding increased histidine and taurine concentrations simultaneously was studied, as well as investigating the potential effect on cataract incidence when feeding moderately elevated histidine level and varying concentrations of dietary zinc and fat. Results showed that increasing dietary histidine levels had a cataract-preventive effect. Adding 5% NaCl to the feed before and during smoltification also reduced cataract frequency and severity. This effect of increasing dietary NaCl level in freshwater seemed to some extent to overrule the effect of increasing dietary histidine on cataract formation in sea water. Fluctuating water salinity and increases in water temperature were also identified as factors contributing to cataract development. No cataract-preventive effects of feeding taurine, zinc, or dietary fat above recommended levels were found. This series of studies showed that several factors contribute to cataract development in farmed Atlantic salmon, and that interaction between factors may be involved.

The specific growth rate (SGRd) of juvenile Fenneropenaeus chinensis shrimp was measured over 35 days under different light intensities: 0, 50, 300, 1300 and 5500 lx. The SGRd of the shrimp under 5500 lx was only 29.4%, 27.1%, 21.1% and 19.7% of those under 0, 1300, 50 and 300 lx, respectively (P

We conducted two experiments on Shubenacadie River stock of Morone saxatilis fed trout pellets. Experiment 1 compared juveniles of ca. 40 and 550 g initial body weight in hard freshwater (FW) for 73 days at either 20, 24 or 28 °C. Experiment 2 lasting 115 days compared 40, 300 and 800 g fish in either FW or seawater (SW, 30 ppt) at either 16 or 23 °C. Body weight, food intake and food conversion ratio (FCR) responses were analyzed as repeated measures, with initial weight as a covariate. Fish grew well in both FW and SW; however, the final mean weight was slightly higher in FW by 3–14% among all size classes, and significant (P

Taiwan abalone Haliotis diversicolor supertexta (13–16 g) were challenged with Vibrio parahaemolyticus at a dose of 2×10 4 colony-forming units (cfu) abalone −1 previously incubated in TSB medium for 24 h, then placed in water having concentrations of dissolved oxygen (DO) at 7.70, 5.61, 3.57 and 2.05 mg l −1 . Onset of mortality occurred after 6-h exposure to 2.05 mg l −1 DO, and after 12-h exposure to 3.57 and 5.61 mg l −1 DO. Cumulative mortality of abalone at 2.05 mg l −1 DO was significantly higher than that at 3.57 mg l −1 DO, and cumulative mortality of abalone at 3.57 and 5.61 mg l −1 DO was significantly higher than that at 7.70 mg l −1 DO after 24 h. Abalones which had been placed in water for 0 to 96 h at 7.70, 5.61, 3.57 and 2.05 mg l −1 DO were examined for the total haemocyte counts (THC), phenoloxidase activity, respiratory burst, phagocytic activity and clearance efficiency. No significant differences in THC and respiratory burst of abalone were observed among four treatments after 6 h. The abalone following 24-h exposure to 2.05 mg l −1 DO decreased significantly its THC and respiratory burst by 27% and 24%, respectively. Phenoloxidase activity increased significantly by 38% and 69% when abalones were exposed to 3.57 and 2.05 mg l −1 DO after 24 h, respectively. Phagocytic activity and clearance efficiency to V. parahaemolyticus decreased significantly for the abalone following 12-h exposure to 3.57 mg l −1 DO, respectively. It is concluded that DO as low as 3.57 and 2.05 mg l −1 causes depression in immune system of H. diversicolor supertexta , and increases its susceptibility to V. parahaemolyticus infection.

The combined effects of temperature and salinity on the hatching success, survival and development of the larval stages of Penaeus merguiensis were investigated in a 4×2 factorial designed experiment employing two temperatures (29±1 and 33±0.5 °C) and four salinities (25, 30, 35 and 40 ppt). Best percentage of hatch was obtained at 33 °C and 35 ppt (87%) followed by 29 °C and 35 ppt (82%). Similarly during naupliar stages, high survival rate was obtained at 33 °C and 35 ppt (89%). Metamorphosis cycle during the protozoeal stages (protozoea 1 to postlarva 1) was extended and survival rate decreased at 25 ppt. Development to PL1 was faster at 33 °C (7–8 days) as compared to 29 °C (8–10 days) regardless of the salinity levels. Maximum survival during the protozoeal stages was at 35 ppt followed by 48% at 33 °C and 45% at 29 °C. Results showed that salinity exerted a greater influence than temperature on the survival and development of larvae. Based on the results, the best temperature–salinity combination for larval survival and metamorphosis of P. merguiensis is 33 °C and 35 ppt. A salinity range of 30–35 ppt is ideal for larval development.

A 6-week experiment (August 10 to September 21, 1999) was conducted to determine the effect of urchin size and diet on gonad enhancement of the green sea urchin Strongylocentrotus droebachiensis. Sea urchins were collected from the wild and divided into four size classes—30.0–39.9, 40.0–49.9, 50.0–59.9, and 60.0–73.0 mm test diameter—each size group being split into two dietary treatments [prepared feed or kelp (Laminaria longicruris and/or Laminaria digitata)]. The experiment was a 4×2 completely crossed design. A number of gonad attributes were quantified at the beginning and end of the experiment including: wet weight, percent yield, percent water, colour, texture, firmness, and taste. The percent change of these variables over the 6-week period was calculated. Colour was assessed subjectively by eye using colour ratings and objectively with a reflected-light, fibre-optic spectrophotometer to generate CIE L* (lightness), a* (hue), and b* (chroma) values. Gonad taste was subjectively evaluated at the end of the experiment. Results from experimental sea urchins were compared and contrasted with those of wild specimens collected from the source population at the end of the experiment. Percent gonad yield at the end of the experiment and percent increase in percent gonad yield over the 6-week period was significantly greater in urchins fed the prepared diet than in those fed kelp. Percent gonad yield was highest in the 40.0–49.9 mm group, followed closely by the 50.0–59.9 and 30.0–39.9 mm size groups, whereas percent increase in percent gonad yield decreased with increasing urchin size. Gonad colour at the end of the experiment was significantly better in urchins fed the prepared diet than in those fed kelp (as judged by colour ratings, a*, and b*) and was better in smaller than larger individuals (as judged by colour ratings, L*, and a*). Percent change in gonad colour ratings decreased and percent change in L* and a* increased with increasing urchin size. Urchin size and feed type had no significant effect on gonad texture, but both factors significantly influenced gonad firmness and taste. Gonads of urchins fed the prepared diet were significantly softer and had significantly more water than those fed kelp. Gonad firmness and percent change in firmness increased with increasing urchin size. Kelp-fed individuals produced significantly better tasting gonads than those fed the prepared diet. The largest urchins produced the best tasting gonads of those fed kelp, but the smallest individuals had the best gonad taste of those fed the prepared diet. Overall, considering both gonad quantity and quality factors, sea urchins of 40.0–49.9 mm test size were deemed to be the most promising for gonad enhancement operations.

During the production of sunshine bass, the fish are graded several times to avoid loss due to cannibalism. Such grading of fish that may exhibit sexually dimorphic growth could result in changing the sex ratio of populations raised for food production. A preferred gender exists for most aquaculture species. We have found that, during the first year, male sunshine bass appear to grow faster than females; however, females grow faster during the second year and are usually heavier when the fish are harvested. Feeding 17-α-methyltestosterone did not increase the growth of fingerling fish; however, feeding estradiol decreased growth, apparently by decreasing feed consumption. Immersion treatment of 4-day-old fry for up to 8 h with 17α-methyltestosterone or estradiol did not change the sex ratio. Treatment of 60- or 103-day-old fish for 40 days with estradiol in the feed resulted in all female fish. 17α-methyltestosterone treatment during the earlier period resulted in intersex fish, and treatment of 103-day-old fish did not change the sex ratio. Direct feminization with estradiol can be achieved during a period of development in which direct masculinization with 17α-methyltestosterone is not effective.

Atlantic salmon (Salmo salar L.) smolts (out-of-season), average weight: 42–77 g were exposed during 40 days to three water flow rates: 0.55–0.71 l kg−1 min−1 (high), 0.25–0.31 l kg−1 min−1 (medium) and 0.15–0.20 l kg−1 min−1 (low) at two different salinity levels, 4.5 ppt (High) and 1.6 ppt (Low). There were two replicate tanks in each group. Oxygen was added to the inlet water to maintain discharge water oxygen concentration higher than 7.5 mg l−1 at 8–9 °C. pH was 6.1–6.4 and 6.3–6.7 in the tanks supplied low and high salinity water, respectively. Concentrations of carbon dioxide were 14 mg l−1 at low flow, 10 mg l−1 at medium flow and 7 mg l−1 at high flow. After 6 weeks, all groups were transferred from the brackish water to normal seawater. Gill Al accumulation was low in all groups at the end of the brackish water period (highest mean value was 11 μg Al g−1 gill tissue). However, gill Al accumulation was significantly higher in the low salinity groups compared to the high salinity groups (p

The responses of embryos and juveniles of the pearl oyster, Pinctada imbricata, to variation in temperature and salinity were investigated to assist hatchery production and farming. Embryos were incubated at temperatures in the range 14–26 °C and salinities in the range 11–35 ppt. Embryos did not develop to D-veliger stage at 14 °C and at salinities of 26 ppt or less. Within the salinity range 29–35 ppt, the percentage embryos developing to D-veliger stage increased significantly with increasing salinity. Within the temperature range 18–26 °C, increasing temperature increased the rate of development as well as the number of embryos developing to D-veliger stage within 40 h. Juvenile P. imbricata (17 mm shell height) held at temperatures in the range of 14–24 °C were exposed to salinities in the range of 11–35 ppt. Spat formed byssal attachments most rapidly at salinities of 29 and 32 ppt, irrespective of temperature. At these salinities, >70% of oysters formed byssal attachments to the aquaria walls within 6 h. Outside this narrow salinity range, the rate of byssal attachment decreased and ceased altogether at salinities of 17 ppt or less. Temperature also affected byssal attachment although the impacts were not as great as those of salinity. Within the optimal salinity range (29–32 ppt), the rate of byssal attachment was fastest at 18 °C, where up to 80% of oysters had attached within 4 h. This rate was slightly greater than that observed at 22 °C, which in turn exceeded those observed at 14 and 26 °C. Salinity and temperature also affected survival. Irrespective of temperature, survival was high at salinities of 32 and 35 ppt. By contrast, high rates of mortality occurred within 7 days at salinities of 23 ppt or less. Onset of mortality was most rapid and overall mortality highest at the two extremes in temperature tested, 14 and 26 °C.

A 12-week study was conducted to examine the influence of light regime on food intake and growth in juvenile (ca. 3.5 g) largemouth bass ( Micropterus salmoides ). Fish were reared in 15-l aquaria either under an alternated light/dark cycle (12L:12D; L from 6:00) or under continuous light (24L:0D), and were weighed every 3 weeks. They were fed by hand once a day at 8:00, with fish in each aquarium being provided with 2% of the tank biomass (re-calculated every 3 weeks). After each meal, uneaten pellets were counted and food intake estimated. Fish reared under continuous light grew faster than those under day–night alternation, primarily because feed consumption of fish was greater under 24L:0D than under day–night alternation.

The mass evolution of phospholipids and triacylglycerols of mullet fry was studied using a decreasing salinity (0.5‰) at constant temperature. After 4 weeks of acclimation (0.5‰), high concentrations of phospholipids (9.75 mg/g wet weight) and triacylglycerols (49.77 μmoles/g w/w) were observed in fry acclimated in seawater (35‰) compared to fry in freshwater (0.5‰) which had levels of 6.56 mg/g w/w and 7.32 μmol/g w/w, respectively. Significantly, high levels of phosphatidylcholine (PC) were observed in fry acclimated to freshwater (960.48 μg/g w/w) compared to those in seawater (591.97 μg/g w/w). Radioactivity distribution, after injection of labelled acetate at 14 C, was significantly higher in fry acclimated to seawater in the triacylglycerol. However, high levels of radioactivity were incorporated in PC in fry acclimated to freshwater. High levels of PC in fry acclimated to freshwater could serve as precursor synthesis of triacylglycerols. The enrichment of food for mullet fry with lecithin (PC) is necessary during acclimation before their introduction into freshwater (0.5‰) to reduce mortality.

Litopenaeus vannamei juveniles (total length 56±9.6 mm) were exposed to different concentrations of nitrite-N (nitrite as nitrogen), using a static renewal method at salinity levels of 15‰, 25‰ and 35‰ (g/kg) pH 8.02 and 18 °C. The 24-, 48-, 72-, 96- and 144-h LC50 value of nitrite-N on L. vannamei juveniles were 187.9, 142.2, 92.5, 76.5, 61.1 mg/l at 15‰; 274,1, 244.0, 224.8, 178.3, 152.4 mg/l at 25‰; 521.2, 423.9, 375.0, 321.7, 257.2 mg/l at 35‰, respectively. As the salinity decreased from 35‰ to 15‰, susceptibility of nitrite-N increased by 277%, 298%, 405% and 421% after 24-, 48-, 72-, 96- and 144-h exposure, respectively. The “safe level” for rearing L. vannamei juveniles was estimated to be 6.1, 15.2, 25.7 mg/l for nitrite-N in 15‰, 25‰ and 35‰, respectively. The relationship between LC50 of nitrite-N (mg/l), salinity (S) and exposure time (T) is as follows: LC50=123.0182+0.3657S−0.6072T (R2=0.9847).

Six size groups of red abalone Haliotis rufescens (geometric mean shell lengths: 21, 25, 33, 66, 81 and 98 mm) were reared on a macroalgal diet for 4 months at seven different temperatures between 11 and 22 jC. The results demonstrate that red abalone exhibit size dependent variation in growth potential and temperature optimum for growth. The maximum growth rate was found to have a skewed, third degree polynomial relationship with shell length, reaching a maximum of 111 Am day � 1 at 38 mm shell length. The temperature optimum for growth was found to have a symmetrical, concave relationship with shell length from 16 mm to maturity, reaching a peak of 17.8 j Ca t 44 mm shell length. The minimum grow-out time from spat to market size on an optimum temperature regime was predicted less than 2 years. The results from the present study could contribute to an increase in the potential yield from landbased abalone farming. D 2003 Elsevier Science B.V. All rights reserved.

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

We studied the effect of varying response intervals of a self-feeding system on growth and feeding profiles of rainbow trout (Oncorhynchus mykiss) fry (1.53±0.55 g, mean±S.D.). Triplicate groups of 40 fish were fed a commercial trout feed for 49 days via self-feeders with response intervals adjusted to 2, 4, 15, or 60 s and a fixed reward level of 0.03 g (0.05% of initial biomass) per activation. In all groups, feeder activation occurred exclusively during the light period (07:00–19:25) with marked peaks at the artificially induced dawn and dusk. As the experiment progressed, the number of feeder activations during peak periods significantly increased in the 2 and 4 s response interval groups, but not the 15 and 60 s groups. Throughout the experiment, the amount of feed dispensed daily increased in all response interval groups. However, as the experiment progressed, the amount of feed dispensed in the 15 and 60 s groups gradually became less than the 2 and 4 s groups. There were significant negative relationships between the response interval and the feeding rate, final body weight (BWf), specific growth rate (SGR), and condition factor (CF) (P

To better understand how photoperiod and body size interact to affect age at maturity, PIT-tagged 2-year-old Salvelinus alpinus (ca. 300 g, n=330) were reared in fresh water from February 3 under four treatments, either 18-h light/6-h dark (LD18:6) for 42 days then LD8:16 (long–short); LD18:6 for 42 days then simulated natural (long–ambient); constant LD18:6 (constant–long); or simulated seasonal photoperiod cycle (control). Temperature was 10 °C. In November, the incidence of maturity in the long–short treatment was reduced to 44% among males and 20% among females, compared to 83% and 50% in the control (p 1 kg and immature) by over four-fold. The long–ambient treatment also reduced maturation (p

During smolting, cortisol acts on the gill through intracellular corticosteroid receptors (CR). Regulation of CR concentration ( B max ) and dissociation constant ( k d ) by environmental factors, however, has not been investigated. We subjected juvenile Atlantic salmon ( Salmo salar ) to changes in photoperiod and temperature to determine the effect on gill CR B max and k d . Cortisol, growth hormone (GH), insulin-like growth factor 1 (IGF-1), thyroxine (T 4 ), and triiodothyronine (T 3 ) were measured to determine endocrine factors that correlated with changes in CR B max and k d . Gill Na + ,K + -ATPase activity was measured as an indicator of smolting. Control fish were maintained under ambient Connecticut River water temperatures and natural photoperiod (LDN). In the first experiment, fish were also reared at elevated temperature (constant 10 °C), or long day photoperiod (LD 16:8; 16 h light), or a combination of these two treatments. In the second experiment, fish were subjected to an advanced river temperature regime, or short day photoperiod (LD 9:15; 9 h light), or a combination of these two treatments. Seasonal changes in CR B max were found to be significantly affected by temperature, but not photoperiod. A decline in CR B max occurred when mean daily temperature increase exceeded 1.5 °C per week, preceding the increase in gill Na + ,K + -ATPase activity. CR B max was found to be correlated positively with T 4 and negatively with IGF-1. Gill CR k d changed significantly over the spring, but manipulation of temperature and photoperiod had little effect. CR k d was found to be positively correlated with gill Na + ,K + -ATPase activity, plasma GH, cortisol, IGF-1 and T 4 . Temperature appears to influence seasonal changes in CR B max observed, whereas endocrine factors appear to be more closely related to seasonal changes in CR k d .

We sampled cultured juveniles of the ayu Plecoglossus altivelis that would be used for river stocking, to evaluate histologically the development of the organs that are important for immunological competence of the fish. These samples included hatchery-produced fish reared in three different facilities (sample A), fish captured in Lake Biwa when they were larvae and cultured by three different fish farmers (B), and wild juveniles as the control. Each sample consisted of at least 10 fish. Histological observation and following quantification showed clear positive correlation of the thymus volume and the body length of the wild fish. However, the fish in each 2 groups of the samples A and B had significantly smaller thymuses than those of the wild fish of corresponding body lengths. Congestive splenomegaly was often observed in the cultured fish for both groups. To know the rearing conditions that affect thymus development, a preliminary experiment was conducted in which larval ayu were reared in aquaria for 3 months in four different rearing conditions with the combinations of two different water temperatures (13.8 and 17.2 °C) and two different stocking densities (0.25 and 2.5 kg/m3 at the start of the experiment). The result showed that both the high water temperature and the high rearing density suppressed development of the thymus significantly, whereas the fish reared in the combination of low water temperature and low rearing density developed the thymuses of the comparable size to those of the wild fish. These results suggest that inappropriate culture conditions may suppress the thymus development, even if the fish appear to grow normally.

Current Atlantic salmon farming practice induces early smoltification with artificial photoperiod regimes, however the importance of these photoperiods on parr maturation and interactions with smoltification are poorly understood. These questions were addressed in the present investigation, which examined the effects of photoperiod manipulation on the development, maturation and smoltification of individually tagged parr. Approximately 9000 salmon parr from a high grilsing stock were exposed to continuous light (LL) from first feeding. Three sub-groups of 2400 parr, each sub-group in triplicate tanks, were then exposed to an 8-week “winter photoperiod” (LD 10:14) starting on either the 18th May, the 9th August or the 20th September (defined, respectively, as the May, August and September groups). Following the artificial winter, each group was returned to LL. A fourth group of 1600 fish was maintained in replicate tanks on LL throughout. The highest levels of maturation (approx. 20%) were recorded in the May group. August and September groups showed low levels of maturity ( It is concluded that the photoperiod to which parr are exposed early in their life acts as an important trigger for precocious maturation but does not necessarily phase shift the endogenous rhythm which is thought to control its timing. Smoltification is strongly influenced by the timing of exposure to winter photoperiod with clear evidence indicating that maturation and smoltification are not mutually exclusive processes.

Exposure of Atlantic salmon ( Salmo salar L.) smolts in freshwater to environmental levels of the oestrogenic chemical 4-nonylphenol (4-NP) (concentrations 5–20 μl l −1 ) during the peak migration period had no significant effect on gill Na + K + ATPase activity, plasma vitellogenin (VTG) levels or hypoosmoregulatory performance as indicated by survival in sea water. However, where smolts were exposed to mixtures of 4-NP and the pesticide atrazine at concentrations of 5.0/1.0 and 10.0/2.0 μg l −1 , respectively, there were significant differences in the gill Na + K + ATPase activity, plasma Cl − and Na + and increased mortalities when transferred to seawater. Smolts retained for a short period in an estuary with high levels of oestrogenic contamination showed no significant differences in gill Na + K + ATPase activity, plasma vitellogenin (VTG) levels or hypoosmoregulatory performance compared to fish maintained in an adjacent uncontaminated estuary. The results of the study are discussed in relation to the effects of environmental levels of oestrogenic contaminants on smoltification and migration in wild salmon.

Atlantic salmon ( Salmo salar ) smolts originating from wild (Imsa) and selected (AquaGen) strains were maintained on simulated natural photoperiod (SNP) or constant light (LL) in replicate tanks between 3 December 1998 and 26 May 1999. Gill Na + ,K + -ATPase activity, plasma growth hormone (GH) levels, condition factor (CF) as well as individual food intake, growth and food conversion were monitored regularly in all groups during the experimental period. Freshwater temperature was kept constant at approximately 12 °C. In both strains, GH levels and gill Na + ,K + -ATPase activity rose steadily in the SNP groups, whereas the abrupt increase in day-length caused a significant increase in GH levels within 4 weeks, concurrent with an increase gill Na + ,K + -ATPase activity. The close relationship between GH levels and gill Na + ,K + -ATPase activity indicates that GH plays and important role in the development of hypo-osmoregulatory ability during smolting. Overall, a higher growth rate was seen in smolts from the AquaGen strain compared with the Imsa strain. No differences in food consumption were seen between strains, whereas an improved food conversion was observed in smolts from the AquaGen strain. Photoperiod was found to enhance growth through stimulation of food intake. It is concluded that the observed differences in growth and food conversion between wild and selected smolts are genetic, and probably reflect the fact that the AquaGen fish have been bred for rapid growth for several generations.