Growth and osmoregulation in Atlantic salmon (Salmo salar ) smolts in response to different feeding frequencies and salinities

Groups of Atlantic salmon (Salmo salar) yearling smolts were reared in duplicate tanks supplied with freshwater or seawater, and subjected to different feeding frequencies, 100% (fed every day), 50% (fed every other day), 25% (fed every forth day) and 0% (starved), from 26 May to 26 July. After 8 weeks, all the groups were re‐fed in excess for 6 weeks. Fish were maintained on their respective a priori salinity treatments during the 6‐week follow‐up period. Starvation for a period of 8 weeks in freshwater resulted in a loss of hypo‐osmoregulatory ability when smolts were challenged with seawater and unfed smolts maintained in freshwater were unable to adapt to seawater in mid‐July. Ration levels influenced the growth rate and body size significantly. The overall growth rate was higher in freshwater than at corresponding rations in seawater. Partial compensatory growth was observed in the 0 and 25% groups following re‐feeding. Branchial Na⁺,K⁺‐ATPase (NKA) activity decreased rapidly in unfed smolts in freshwater and was the lowest in the starved group, whereas an initial increase was observed in those groups reared in seawater. After re‐feeding NKA activity differences decreased between the former feeding groups. Our results suggest that nutritional factors and/or energy levels are critical for the maintenance of hydro‐mineral balance of salmon smolts.     

Effect of the daily meal time on the growth of rainbow trout fed different ration levels

This study examined the effect of ration level and time of delivery of a single daily meal on the growth performance of rainbow trout held under constant water temperature and a natural photoperiod. Two similar trials were conducted, the first from March to July, 1992, using ration levels of 0.5, 1.5 and 2.5% BW d^–1 and the second from August 1992 to January 1993, using ration levels of 1.5, 2.0 and 2.5% BW d^–1.In five of the six treatment groups (three ration levels × two seasons), when the daily meal was presented in the post-dawn period the growth rate was lower than in trout fed at either mid-light or pre-dusk. No time-of-feeding effect was found when trout were fed excess rations. Specific growth rate (SGR) was not affected by feeding time, but was correlated with ration level; furthermore, there was a significant increase in SGR during the first section of the first trial and a significant decrease in the SGR throughout the duration of the second trial.Ration level was significantly correlated with condition factor, carcass visceral adipose tissue content and skeletal muscle lipid content, but there was no effect of the timing of the daily meal on these variables.     

Effects of salinity and pH on ion-transport enzyme activities, survival and growth of Litopenaeus vannamei postlarvae

Effects of the salinity and pH on ion-transport enzyme activities, survival and growth of Litopenaeus vannamei postlarvae were investigated. Shrimp were transferred from salinity 31‰ and pH 8.1 to different salinity levels of 22, 25, 28, 31 (control), and to different pH levels of 7.1, 7.6, 8.1 (control), 8.6 and 9.1. The results showed ion-transport enzyme activities and weight gains of postlarvae were significantly affected by salinity and pH variation, which had no obvious effect on survival rate. The changing salinity affected the activities of total ATPase and Na⁺-K⁺-ATPase notably (F > F_0.05), meanwhile, non-significantly to the activities of V-ATPase, HCO₃⁻-ATPase. Within 48 h of salinity changing, the activities of ATPase, Na⁺-K⁺-ATPase in each treatment group gradually increased with the sampling time and reached their climax at 48 h, and then stabilized, showing negative correlation with salinity. The changing of pH affected greatly the activities of ATPase, Na⁺-K⁺-ATPase, V-ATPase and HCO₃⁻-ATPase (F > F_0.05), the activities of ATPase, Na⁺-K⁺-ATPase in each treatment group (pH = 7.1, 7.6, 8.6, 9.1) showed peak change within 72 h and stabilized afterwards, and the Na⁺-K⁺-ATPase activities came back to the level of the control group; Meanwhile the changing extent of V-ATPase and HCO₃⁻-ATPase activity corresponded with the grads of pH, and these ATPase activities showed negative correlation with pH changing, the activities of V-ATPase, HCO₃⁻-ATPase in postlarvae of each treatment group came to stable level after 24 h. The experiment also indicated the strength order of these ion-transport enzyme activities were as follows: Na⁺-K⁺-ATPase > V-ATPase > HCO₃⁻-ATPase. Na⁺-K⁺-ATPase was the chief undertaker of osmoregulation under the salinity effects, while V-ATPase and HCO₃⁻-ATPase were the chief osmoregulation undertakers under pH changing. In different salinity environment, the contributions of Na⁺-K⁺-ATPase, V-ATPase and HCO₃⁻-ATPase of L. vannamei postlarvae approximately accounted for 62.0-78.0%, 15.9-29.0% and 2.03-4.12% of ATPase activities in total, respectively. Meanwhile, in different pH medium, the contributions of these ATPases approximately accounted for 50.7-67.4%, 21.3-31.8% and 2.15-7.90% of total ATPase activities, respectively. Weight gain of shrimp transferred to salinity 31 (control) and 28‰ was significantly higher than that of shrimp reared at 25 and 22‰, and weight gain of shrimp transferred to pH 8.1 (control) and 8.6 was significantly higher that that of shrimp transferred to pH 7.1, 7.6 and 9.1. It was suggested that during the process of desalting and culturing of postlarvae, the salinity changing should not exceed 3 and pH variety not more than 0.5.     

Influence of salinity on the energetics of gill and kidney of Atlantic salmon (Salmo salar)

The effect of seawater acclimation and adaptation to various salinities on the energetics of gill and kidney of Atlantic salmon (Salmo salar) was examined. Smolts and non-smolts previously reared in fresh water were exposed to a rapid increase in salinity to 30 ppt. Plasma osmolarity, [Na⁺], [Cl^–], [K⁺] and [Mg⁺⁺] increased in both groups but were significantly lower in smolts than non-smolts. Gill Na⁺, K⁺-ATPase specific activity, initially higher in smolts, increased in both groups after 18 days in seawater. Kidney Na⁺, K⁺-ATPase specific activity was not affected by salinity in either group. Gill and kidney citrate synthase specific activity was not affected by seawater exposure in smolts but decreased in non-smolts. In a second experiment, Atlantic salmon smolts reared in fresh water were acclimated to 0, 10 or 30 ppt seawater for 3 months at a temperature of 13–14°C. Gill Na⁺, K⁺-ATPase was positively correlated with salinity, displaying 2.5- and 5-fold higher specific activity at 10 and 30 ppt, respectively, than at 0 ppt. Kidney Na⁺, K⁺-ATPase specific activity was not significantly affected by environmental salinity. Citrate synthase and cytochrome c oxidase specific activities in gill were slightly (6–13%) lower at 10 ppt than at 0 and 30 ppt, whereas kidney activities were lowest at 30 ppt. Oxygen consumption of isolated gill filaments was significantly higher when incubated in isosmotic saline and at 30 ppt than at 0 ppt, but was not affected by the prior acclimation salinity. The results indicate that although high salinity induces increased gill Na⁺, K⁺-ATPase activity, it does not induce substantial increases in metabolic capacity of gill or kidney.     

The effect of dietary sodium chloride on some osmoregulatory parameters of the teleost, Oreochromis niloticus, after transfer from freshwater to seawater

The aim of this work was to determine the effects of supplemental dietary sodium chloride on salt water acclimation of tilapia Oreochromis niloticus. Fish were fed a basal diet supplemented with NaCl (8%) during three weeks in fresh water (FW) and then transferred to salt water (SW) at 15 and 20. Changes in plasma osmolality, chloride ion concentration (Cl^–), plasma level of cortisol and gill Na⁺, K⁺-ATPase activity were measured at 6, 12, 24, 48, 72 and 168 h after transfer to 15SW, while the higher strength SW group (20) was only monitored up to 24 h. Morphological changes in the gill mitochondria-rich (MR) cells were examined in relation to environmental salinity. The changes associated with dietary NaCl were sporadic and of small magnitude. The plasma osmolality and Cl^– increased immediately after transfer up to 12–24 h, but fish fed dietary salt (S) showed lower values than the control group (C). The S group showed higher plasma levels of cortisol than the control, which maintained its initial levels during the experiment. Gill Na⁺, K⁺-ATPase activity of the S group began to increase in the first hours after transfer, reaching maximum at 12 h and returned to basal level at 24 h, while the control group maintained basal levels. The differences between gill Na⁺, K⁺-ATPase activity of S and C fish were significant (p < 0.05) at 12 h. Transmission electron microscopy (TEM) revealed that MR cells in SW show more mitochondria and a more developed tubular system arising from the basolateral membrane. The MR cells of both groups frequently formed a multicellular complex in SW, consisting of a main MR and one or more accessory cells. Such complexes are rarely observed in FW. Some MR cells of fish fed supplemented dietary salt displayed convex apical membrane in FW.     

Influence of cortisol, growth hormone, insulin-like growth factor I and 3,3′,5-triiodo-l-thyronine on hypoosmoregulatory ability in the euryhaline teleost Fundulus heteroclitus

The capacity of cortisol, ovine growth hormone (oGH), recombinant bovine insulin-like growth factor I (rbIGF-I) and 3,3,5-triiodo-l-thyronine (T₃) to increase hypoosmoregulatory capacity in the euryhaline teleost Fundulus heteroclitus was examined. Fish acclimated to brackish water (BW, 10 ppt salinity) were injected with a single dose of hormone suspended in oil and transferred to seawater (SW, 35 ppt salinity) 10 days post-injection. Fish were sampled 24 h after transfer and plasma osmolality and gill Na⁺, K⁺-ATPase activity were examined. Transfer from BW to SW induced significantly increased plasma osmolality but not gill Na⁺, K⁺-ATPase activity. Cortisol (50 g g^–1 body weight) improved the ability to maintain plasma osmolality and to increase gill Na⁺, K⁺-ATPase activity. oGH (5 g g^–1 body weight) also increased hypoosmoregulatory ability and gill Na⁺, K⁺-ATPase activity. A cooperation between oGH and cortisol was observed in increasing hypoosmoregulatory ability but not in increasing gill Na⁺, K⁺-ATPase activity. rbIGF-I (0.5 g g^–1 body weight) alone was without effect in increasing salinity tolerance or gill Na⁺, K⁺-ATPase activity. rbIGF-I and oGH showed a positive interaction in increasing salinity tolerance, but not gill Na⁺, K⁺-ATPase activity. Treatment with T₃ (5 g g^–1 body weight) alone did not increase salinity tolerance or gill Na⁺, K⁺-ATPase activity, and there was no consistent significant interaction between cortisol and T₃ or between GH and T₃. The results confirm the classical role of cortisol as a seawater-adapting hormone and indicate an interaction between cortisol and the GH/IGF-I axis during seawater acclimation of Fundulus heteroclitus.     

Survival, growth and osmolality of greenlip abalone Haliotis laevigata (Donovan 1808) when exposed to different ionic profiles of inland saline water

Two experiments over 21 days were conducted to assess the effect of different ionic profiles (mainly K⁺) of inland saline water (ISW) on the survival, growth, osmoregulation and moisture content of juvenile greenlip abalone Haliotis laevigata. In experiment I, the juveniles were cultured in five different water types: ocean water (OW) as a control, inland saline water (ISW or ISW K⁺₀), ISW fortified with 33%, 66% and 100% K⁺ as in OW (ISW K⁺₃₃, ISW K⁺₆₆ and ISW K⁺₁₀₀ respectively). In experiment II, five different culture media, 100% OW(control), 75% OW mixed with 25% ISW (ISW₂₅), 50% OW mixed with 50% ISW (ISW₅₀), 25% OW mixed with 75% ISW (ISW₇₅) and 100% ISW (ISW or ISW₁₀₀), were tested. Within 21 days, all of the abalone in ISW (ISW K⁺₀ and ISW₁₀₀; Na⁺/K⁺ ratio of 111 L^?1) died compared with 100% survival in OW. One‐hundred per cent K⁺ fortification of ISW increased the specific growth rate (SGR) and serum osmolality of the surviving juveniles. The 96 h acute LC₅₀ value was between ISW₅₀ and ISW₇₅. The increased proportion of ISW in OW resulted in significantly (P<0.05) lower survival, SGR and serum osmolality of juveniles. The moisture content of the juveniles was not influenced by any water type. The results suggested that abalone cannot survive in raw ISW, but survival can increase when it is fortified with K⁺ and ionic ratios of ISW are brought closer to OW by mixing it with OW. Furthermore, abalone survival is influenced by other ions in ISW besides K⁺.     

Replacement of fishmeal with rice protein concentrate in practical diets for European sea bass Dicentrarchus labrax reared at winter temperatures

As no information is available regarding the efficacy of using rice protein concentrate (RPC) to replace fishmeal (FM) in diets for European sea bass (Dicentrarchus labrax), a trial was conducted to determine the optimum inclusion for European sea bass juveniles. Diets were formulated to replace 25%, 50% and 75% of fishmeal with RPC. Additional high level inclusion diets (50% and 75%) were supplemented with lysine and methionine to determine if these were limiting factors. Fish (18.0 ± 0.06 g) were fed the experimental diets for 12 weeks. The final mean weight and specific growth rate (SGR) were significantly higher in fish fed the control diet (diet FM) and low level RPC (diet RPC25) than in fish fed the other diets. The supplementation of the amino acids had a positive effect on growth, elevating the final weight of the high level RPC (RPC75 + AA) group above that of the non‐supplemented group (RPC75). However, this was still not comparable to fish fed FM and RPC25 diets. No significant differences in body composition were observed. A digestibility study demonstrated an inverse relationship between elevating inclusion levels of RPC and apparent digestibility coefficients (ADCs) for dry matter and lipid, with significantly lower values than the control being observed with RPC inclusions above 25%. The mesenteric fat index followed this trend. Circulating leucocyte levels, leucocyte ratios and serum lysozyme activity remained unaffected by dietary treatment. However, compared with the control group, fish fed RPC75, RPC50 + AA RPC75 + AA displayed significantly lower haematocrit values. The present study demonstrates that the inclusion of RPC at 140 g kg^?1 (effectively replacing 25% of FM content) does not compromise European sea bass growth performance, body quality or basic haematological parameters. It is suggested that future studies including higher levels test the efficacy of additional amino acid supplementation (e.g. tryptophan).     

Mitochondrial enzyme and Na+, K+-ATPase activity,and ion regulation during parr-smolt transformation of Atlantic salmon (Salmon salar)

Atlantic salmon (Salmo salar) exposed to either simulated natural photoperiod (SNP) or continuous light (L24) were used to examine developmental changes in the presence and absence, respectively, of the parrsmolt transformation. Plasma osmolarity and ion concentrations were unaffected by photoperiod treatment. Gill Na⁺, K⁺-ATPase specific activity increased 150% between February and June in SNP fish and was low and unchanged in L24 fish. Kidney Na⁺, K⁺-ATPase specific activity varied within similar, narrow limits in both groups. Citrate synthase of liver, gill and kidney, expressed as specific activity or activity/g total body weight (relative activity), increased 25–60% between March and June in SNP fish. With the exception of kidney relative activity, citrate synthase activity declined to initial (March) levels by August. Liver, gill and kidney cytochrome c oxidase activity of the SNP group underwent similar though less marked changes. Liver, gill and kidney citrate synthase and cytochrome c oxidase activities of the L24 group remained relatively constant between March and August, and where significant differences occurred, they were lower than those of the SNP group. These results indicate that respiratory capacities of the liver, gill and kidney increase in smolls concurrent with preparatory osmoregulatory changes, and subsequently decline. The findings are consistent with a hypothesized transient increase in catabolic activity during the parr-smolt transformation that may be due to the metabolic demands of differentiation.     

Enhanced hypoosmoregulatory response to growth hormone after cortisol treatment in immature rainbow trout,Salmo gairdneri

The growth-independent effect of ovine growth hormone (oGH) and oGH + cortisol treatment on seawater (SW) adaptation in immature rainbow trout, Salmo gairdneri was investigated. Fish were injected every second day with saline, 2.0 μg oGH/g or 2.0 μg oGH + 8.0 μg cortisol/g for a maximum of 8 injections in freshwater (FW). Subgroups were transferred to 28‰ SW after 4 or 8 injections, and changes in plasma Na⁺ and Cl⁻, muscle water content and gill Na⁺/K⁺-ATPase activity were measured. In both of the hormone-treated groups retained in FW, gill Na⁺/K⁺-ATPase activity and interlamellar chloride cell density increased. The effects were most pronounced in the oGH + cortisol group after 2 weeks of treatment. After transfer to SW most of the control fish died due to the osmotic stress, whereas in the hormone-treated groups, mortality was low and there was a positive correlation between pretransfer gill Na⁺/K⁺-ATPase and the ability to maintain ionic-osmotic homeostasis after SW transfer. After two weeks of oGH + cortisol treatment, gill Na⁺/K⁺-ATPase activity was maximal. In contrast, after SW transfer, Na⁺/K⁺-ATPase activity increased further in the oGH-treated group. This group regulated ionic-osmotic parameters less effectively than the oGH + cortisol-treated group. The data indicate that GH and cortisol are important hormones in the regulation of hypoosmoregulatory mechanisms in S. gairdneri.     

Compensatory growth in Atlantic halibut: Effect of starvation and subsequent feeding on growth, maturation, feed utilization and flesh quality

A group of juvenile Atlantic halibut (mean, SD, 199.5 g, 44.7) was split into two experimental groups: one group was fed in excess twice a day and later five days a week (i.e. Control group), and the other group was starved for 5 weeks and then subsequently re-fed for 10 weeks (i.e. 5/10 starvation/re-fed group). This treatment was repeated for three years until the fish were harvested (mean final weight, 4.4 kg). A size +specific compensatory response was seen; partial compensation was observed in halibut weighing less than 500 g whereas full recovery growth was seen in halibut over 2 kg. Food consumption and feed conversion efficiency was measured during two full 5/10 starvation/re-fed cycles. The Control group consumed 86% more food in the measurement period, whereas the FCE 40% higher in the 5/10 starvation/re-fed group (FCE = 0.95) compared to the Control group (FCE = 0.68). In males lower gonadosomatic index (2.2 vs. 3.0) and plasma 11-ketotestosterone (0.22 vs. 1.26 ng ml^− 1) levels in the 5/10 starvation/re-fed group were observed during late winter and spring of 2006 (age 3 years) indicating higher age at 1st maturity. Starvation had a significant effect for improving the quality as starved fish had higher muscle pH (6.4 vs. 6.2), less gaping (0.1 vs. 0.3) and harder texture (61.4 vs. 57.6 N). Overall, the rearing on a repeated 5/10 starvation/re-fed regime for 3 years led to full growth compensation, higher feed conversion efficiency, lower male maturation and improved flesh quality.     

Osmoregulation in the mudskipper,Boleophthalmus boddaerti I. Responses of branchial cation activated and anion stimulated adenosine triphosphatases to changes in salinity

The mudskipperB. boddaerti, was able to survive in waters of intermediate salinities (4–27). Fish submerged in dechlorinated tap water suffered 60% mortality by the fifth day while 60% of those in 100% sea-water (sw) died after the third day of exposure. After being submerged in 50% or 80% sw for 7 days, the plasma osmolality, plasma Na⁺ and Cl^– concentrations and the branchial Na⁺ and K⁺ activated adenosine triphosphatase (Na⁺,K⁺-ATPase) activity were significantly higher than those of fish submerged in 10% sw for the same period. However, the activities of the branchial HCO₃ ^– and Cl^– stimulated adenosine triphosphatase (HCO₃ ^–,Cl^–-ATPase) and carbonic anhydrase of the latter fish were significantly greater than those of the former. Such correlation suggests that Na⁺,K⁺-ATPase is important for hyperosmotic adaptation in this fish while HCO₃ ^–-Cl^–-ATPase and carbonic anhydrase may be involved in hypoosmotic survival.     

Conjugated linoleic acid affects growth performance,hepatic fatty acid profile and lipid metabolism in juvenile Synechogobius hasta

This study was conducted to determine the effect of dietary CLA (Conjugated linoleic acid) levels on growth performance, fatty acid profiles and lipid metabolism of liver in Synechogobius hasta. Fish were fed six diets with fish oil replaced by 0 (control), 5, 10, 15, 20 and 25 g kg^?1 CLA for 8 weeks. Weight gain, WG, and SGR (specific growth rate) tended to increase when dietary CLA levels increased from 0 to 10 g kg^?1 and then decline with further increasing dietary CLA levels to 25 g kg^?1. FCR (feed conversion ratio) showed contrary trend with WG and SGR. The reduced VSI (vicero somatic index) and increased HSI (hepatosomatic index) were observed in fish fed increasing dietary CLA levels. Whole‐body lipid content declined, but hepatic lipid content increased with increasing dietary CLA levels. Dietary CLA modified total percentages of the main groups of fatty acids in liver. Hepatic 6PGD, ME and ICDH activities increased with increasing dietary CLA levels. FAS and G6PD were very variable and not related to dietary treatments. CPT I activities showed no significant differences among the treatments. Based on second‐order polynomial regression analysis of WG and FCR against dietary CLA level, 8.7–10.1 g kg^?1 was indicated to be the optimal dietary CLA range for maximum growth and feed utilization for S. hasta.     

Evaluation of pea protein isolate as alternative protein source in diets for juvenile tilapia (Oreochromis niloticus)

To evaluate isolated pea protein as feed ingredient for tilapia (Oreochromis niloticus) juveniles, triplicate groups were fed with four isonitrogenous [crude protein: 421.1–427.5 g kg⁻¹ in dry matter (d.m.)] and isoenergetic (gross energy: 20.46–21.06 MJ kg⁻¹ d.m.) diets with varying protein sources for 8 weeks. Fish meal-based protein content of diets was substituted with 0% (diet 100/0=control group), 30% (diet 70/30), 45% (diet 55/45) and 60% (diet 40/60) isolated pea protein. Tilapia juveniles with an initial body weight of 2.23–2.27 g were fed in average at a level of 5% of their body weight per day. Highest individual weight gain (WG: 21.39 g) and specific growth rate (SGR: 4.21% day⁻¹) and best feed conversion ratio (FCR: 0.90) were observed in tilapia fed diet 100/0, followed by fish-fed diet 70/30 (WG: 19.09 g; SGR: 4.03% day⁻¹; FCR: 0.98), diet 55/45 (WG: 16.69 g; SGR: 3.80% day⁻¹; FCR: 1.06) and diet 40/60 (WG: 16.18 g; SGR: 3.74% day⁻¹; FCR: 1.06). Although fish fed diet 100/0 showed the best performance, inclusion of 30% protein derived from pea protein isolate resulted in a growth performance (in terms of WG and SGR) that did not differ significantly from diet 100/0 in contrast to fish fed diet 55/45 and 40/60. Crude ash content in the final body composition of the experimental fish decreased with increasing dietary pea protein content, while crude protein and lipid content remained equal between the groups. Significant decreasing growth performance and body ash incorporation of tilapia at higher inclusion levels seem to be mainly related to the dietary amino acid profile and phytic acid contents.     

Effects of sulfide on K+ flux pathways in red blood cells of crucian carp and rainbow trout

The effect of sulfide on K⁺ influx pathways was measured in red blood cells (RBCs) of sulfide-sensitive rainbow trout (Oncorhynchus mykiss) and sulfide-tolerant crucian carp (Carassius carassius). In trout RBCs, maximal inhibition of Na⁺, K⁺-ATPase was attained at 10 mol l^–1 sulfide and amounted to 32% without being influenced by pH between 6.7 and 8.3. Ouabain-resistant K⁺ influx in the absence and presence of sulfide was insignificant at pH values between 6.7 and 7.7. At higher pH values ouabain-resistant K⁺ influx increased, but was inhibited to about 15% by 30 mol l^–1 sulfide. In RBCs of crucian carp neither Na⁺, K⁺-ATPase nor ouabain-resistant K⁺ influx were affected by sulfide concentrations up to 850 mol l^–1. Differences in sulfide-sensitivity of K⁺ influx between both species can be based upon different properties of the membrane transporter themselves. The reduced Na⁺, K⁺-ATPase activity in trout RBCs may also result from a slightly reduced (by 9%) ATP level after sulfide exposure. In addition, intracellular sulfide concentrations were higher in trout RBCs as compared to crucian carp. In trout, intracellular sulfide concentrations reached extracellular levels within 5 min of incubation whereas sulfide concentrations in crucian carp RBCs remained about 2-fold lower than extracellular concentrations. Although the physiological basis of sulfide-insensitive K⁺ influx in crucian carp RBCs is currently unknown it may contribute to the extremely high sulfide-tolerance of this species.     

Effect of feeding level on growth and nutrient deposition in rainbow trout (Oncorhynchus mykiss Walbaum) growing from 150 to 600 g

The effects of feeding level on growth and energy partitioning were studied in rainbow trout growing from 150 to 600 g. Triplicate groups of fish (initial weight 158 g fish^?1) were fed a practical diet at various feeding levels (25%, 50%, 75% and 100% of near satiation) for 24 weeks at 8.5°C. The final body weights of fish were 235, 381, 526 and 621 g. Restricted feeding levels significantly reduced live weight gain. Feeding levels had less pronounced effects on feed efficiency ratio, which were 0.98, 1.08, 1.02 and 0.83, respectively, for the 25%, 50%, 75% and 100% feeding levels. The growth of fish fed to near satiation was accurately described by the thermal‐unit growth coefficient. The growth data also showed that the widely used specific growth rate was not an appropriate model. Fish fed at the lowest feeding level (25%), which represented a maintenance ration (energy gain was less than 2 kJ fish^?1 day^?1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. The efficiency of energy for growth (k_g) was estimated to be 0.63. The factorial multiple regression approach estimated that the partial efficiencies of metabolizable energy utilization for protein deposition (k_p) and lipid deposition (k_f) were 0.63 and 0.72, and that maintenance energy requirement was about 19 kJ (kg BW^0.824)^?1, for rainbow trout held at 8.5°C.     

Effect of androgens on seawater adaptation in Arctic char,Salvelinus alpinus

Sexually immature two-year old Arctic char (Salvelinus alpinus) were implanted with Silastic capsules containing testosterone or 11-ketoandrostenedione in early spring. Seawater adaptability of the hormone-treated and sham-operated fish was tested periodically from May to August using a 48h seawater challenge test with 25‰ seawater. The sham-operated control fish displayed a seasonal pattern in seawater adaptation, showing a good hypoosmoregulatory ability until mid June followed by a marked increase in plasma sodium and magnesium levels in July and August. Gill Na⁺-K⁺-ATPase activity decreased concurrently with the observed decrease in seawater adaptability. Over the same period the androgen-treated fish displayed a similar pattern in seawater adaptability, however, in May and June the plasma sodium levels were significantly higher in both androgen-treated groups compared to the control group. Plasma magnesium regulation was impaired in both androgen-treated groups in August. Gill Na⁺-K⁺-ATPase activity in the testosterone-treated fish was lower in June compared to the control fish, whereas the activity was not affected by 11-ketoandrostenedione treatment. The results show that while androgens impair the hypoosmoregulatory capacity in Arctic char, the seasonal pattern of seawater adaptability is not affected.     

Fish anesthesia: effects of the essential oils of Hesperozygis ringens and Lippia alba on the biochemistry and physiology of silver catfish (Rhamdia quelen)

The anesthetic activities of the essential oils (EOs) of Hesperozygis ringens (EOHR) and Lippia alba (EOLA) and their effects in silver catfish (Rhamdia quelen) after anesthesia and recovery were investigated. Fish (32.19 ± 1.24 g) were submitted to one of the following treatments for each EO: basal group, control, or anesthesia (150, 300, or 450 μL L^?1 EO). After that the anesthesia was induced or simulated and the biometric measurements were completed, fish were transferred to anesthetic-free aquaria to allow for recovery. Fish were sampled at 0, 15, 30, 60, and 240 min after recovery. At time 0 of recovery, the ventilatory rate was lower in the groups anesthetized with either EO. In comparison with the basal group, control fish showed an increase in plasma glucose, aspartate aminotransferase (AST), and Na⁺ levels and a reduction in Na⁺/K⁺-ATPase activity at 0 min of recovery. Plasma levels of ammonia and Na⁺ were lower in the fish anesthetized with EOLA (450 μL L^?1) and EOHR (all concentrations), respectively, than in the control fish. Additionally, lactate, AST, alanine aminotransferase, K⁺ plasma levels, and gill Na⁺/K⁺-ATPase and H⁺-ATPase activities were higher in the fish anesthetized with either EOHR or EOLA than in the control fish. The EOs promoted slight changes in silver catfish that enabled both an adaptive response and the recovery of most of the measured parameters after 240 min regardless of concentration or EO that was used. These findings support the use of EOHR and EOLA as anesthetics for fish.     

Dietary L‐tryptophan modulates growth and immuno‐metabolic status of Labeo rohita juveniles exposed to nitrite

Effect of nitrite exposure on growth and immuno‐metabolic responses of Labeo rohita fed L‐tryptophan (TRP) was studied. Fish previously fed normal and elevated levels of tryptophan for 60 days were exposed to nitrite (2.0 mg L^?1) for another 45 days with same feeding regime. There were four treatment groups, viz., TRP₀‐N (control), TRP₀+N, TRP_0.75+N (0.75% supplemental tryptophan in the diet) and TRP_1.5+N (1.5% supplemental tryptophan in the diet). Highest weight gain% and SGR were observed in control and lowest in TRP₀+N. Dietary supplementation of elevated levels of tryptophan augmented weight gain% and SGR. Nitrite exposed groups recorded higher catalase, SOD, LDH, AST and ALT activities compared with control. However, activities reduced with additional levels of tryptophan supplementation. Nitrite exposure reduced WBC count, total protein, albumin, globulin and lysozyme activity compared with unexposed group but groups which were fed additional amounts of tryptophan restored total protein, albumin and globulin similar to TRP₀‐N. In conclusion, nitrite exposure had adversely affected growth, increased activities of LDH, AST, ALT, catalase, but decreased WBC, serum protein, lysozyme and acetylcholine esterase activity of L. rohita. Normal requirement of tryptophan was unable to combat nitrite stress. However, dietary fortification with tryptophan (minimum 0.75% of diet + normal requirement) found effective in combating nitrite induced stress.