Dietary methionine requirement of pre‐adult blunt snout bream, (Megalobrama amblycephala Yih, 1955)

A nine‐week feeding trial was conducted to test the hypothesis that an adequate methionine diet might improve growth, feed utilization, body composition and physiology, and biochemical parameters in pre‐adult blunt snout bream Megalobrama amblycephala, whereas a methionine deficiency might have adverse effects on these parameters. Six isonitrogenous and isoenergetics semi‐purified diets (33.0% crude protein, 7.0% crude lipid) were formulated to contain graded methionine levels (0.39–1.54% of dry weight) at 0.25% increments replaced by equal proportions of glycine. Results show that the survival rate (SR) was not significantly affected by the dietary methionine level. Final weight (FW), feed efficiency ratios (FER), weight gain (WG), and specific growth rate (SGR) increased with increasing dietary methionine levels up to 1.00% and then showed a declining trend. Using quadratic regression analysis of FER and SGR, the dietary methionine requirement was estimated to be 0.74% (2.24% of dietary protein) and 0.76% of the diet (2.30% of dietary protein), respectively. Fish fed the 0.39% methionine diet showed significantly lower whole body protein content compared to those fed with 0.85, 1.00 and 1.24% methionine diets (P < 0.05). Whole body moisture, lipid, and ash contents in pre‐adult adult blunt snout bream were not significantly affected. The urea content in fish fed the 0.85% methionine diet was significantly higher than those of fish fed a 0.39, 0.56, 1.24, 1.54% methionine diet (P < 0.05), but not significantly different in fish fed the 1.00% methionine diet (P > 0.05). No significant differences were found in other indexes such as the hepatosomatic index (HSI), viscerosomatic index (VSI), condition factor (CF), albumin (ALB), total protein (TP), alanine aminotransferase (ALT), and spartate transaminase (AST) (P > 0.05). Most important, the optimal dietary methionine level of pre‐adult blunt snout bream should be 0.74–0.76% of the diet (2.24–2.30% of dietary protein).     

Impact of live food on survival and growth of hatchery‐reared sea trout (Salmo trutta trutta L.) parr in the wild

Survival rates and growth parameters of hatchery‐reared sea trout (Salmo trutta trutta L.) fry were determined after stocking in the wild. The larvae were hatchery‐reared for 12 weeks in two groups: fry were fed either on live zooplankton and live chironomidae larvae (LFG), or fed a pellet diet (PFG). The survival rate and specific growth rates were higher in the LFG than in the PFG group. Most effective for hatchery‐reared fish intended for stocking was the natural, live feed. The mean number of chironomid larvae found in the stomachs of fish that were initially captured in the wild was significantly higher in the LFG than in the PFG group. The live diet supplied in the rearing period had a positive impact on the foraging skills of the sea trout fry and their survival in the wild after their release on 24 April 2010.     

The effect of stocking with 0+ year age‐class Atlantic salmon Salmo salar fry: a case study from the River Bush,Northern Ireland

An enhancement programme based on stocking 0+ year age‐class Atlantic salmon Salmo salar, conducted in the River Bush, Northern Ireland, U.K. over the period 1996–2005, was reviewed with reference to the performance and biological characteristics of wild fish. Wild ova to 0+ year fry (summer) survival was c. 8% with subsequent wild 0+ year fry‐to‐smolt survival c. 9%. Stocked unfed 0+ year juveniles gave c. 1% survival to smolt whilst fed 0+ year S. salar stocked in late summer exhibited survival at c. 5%. Stocking with unfed and fed fry contributed to increased smolt production and helped attain local management objectives between 2001 and 2005. Significant differences in biological characteristics were observed between wild and stocked‐origin fish. Wild‐smolt cohorts were dominated by 2+ year age‐class fish on the River Bush whilst smolts originating from fed fry mostly comprised younger 1+ year individuals. The mean mass of 1+ year smolts derived from stocked fed fry was significantly lower than that of wild 1+ year smolts, although these differences were not evident between older age classes. Differences in run timing between wild smolts and smolts derived from stocked fry were also apparent with the stocked‐origin fish tending to run earlier than wild fish. Although the stocking exercise was useful in terms of maximizing freshwater production, concerns over the quality of stocked‐origin recruits and the long term consequences for productivity are highlighted.     

Growth and contribution of stocked channel catfish,Ictalurus punctatus (Rafinesque, 1818): the importance of measuring post‐stocking performance

In this study it was sought to quantify post‐stocking growth, survival, and contribution of advanced size (178 mm total length [TL]) channel catfish Ictalurus punctatus fingerlings, something rarely done. Channel catfish populations were evaluated before (May 2010) and after (May to August 2011 and 2012) stocking. Relative abundance, stocking contribution, and growth were different (P < 0.05) in the two study impoundments (lakes Lone Chimney and Greenleaf, Oklahoma). For fish stocked in Lake Lone Chimney, stocking contribution was lower (3–35%), and average length and weight of stocked fish by age‐2 reached 230 mm TL and 85 g, whereas the stocking contribution (84–98%) and growth in length (340 mm TL) and weight (280 g) were higher by age‐2 in Lake Greenleaf. Given these unambiguous differences of post‐stocking performance, benchmark metrics that represent population‐level information such as relative abundance and average length and weight of the sample masked these significant differences, highlighting the importance of marking hatchery‐fish and then following them through time to determine the effectiveness of stocking. These results suggest that stock enhancement programmes would benefit from studies that quantify post‐stocking performance of hatchery fish.     

Effect of feeding frequency as a rearing system on biological performance,survival, body chemical composition and economic efficiency of Asian seabass Lates calcarifer (Bloch, 1790) reared under controlled environmental conditions

A 70-day rearing trial was done to determine the optimal frequency of feeding on growth performance (GP), feed conversion rate (FCR), cannibalism, survival rate (SR), body chemical composition and economic efficiency of the Asian sea bass. This study tested four different treatments of feeding frequencies (FF), once (T1), twice (T2), three times (T3), and four times (T4) per day. An average initial weight of Asian sea bass fry was 0.2 g (SD = ±0.12) were stocked 10 individuals per m³ (9.14 m × 1.82 m × 1.22 m, L × W × H; water depth 0.61 m) with two replicates per treatment (4 × 2 = 8). Fry were fed a mixture of larval commercial feed and shrimp with a pellet diet containing (46% CP). Initially, the feeding rate of 8% biomass per day was further adjusted according to fish biomass on a weekly basis. Results showed that, the FF significantly affected (p < 0.05) on growth indictors and survival rate (SR). Specifically fry fed three times a day (T3) had the best FBW, FL, SGR, ADWG and FCR followed by T4 and T2 while fry fed one time a day was the lowest in these parameters. Also, VSI, HSI and CF (k) significantly differed among the treatments. The fish whole body content of protein, moisture and ash did not significantly (p < 0.05) be affected by feeding frequency, but lipid content differed and both T3, T4 were the highest. It could be concluded that, increasing FF up to three times a day had a positive effect on weight gain, survival rate and feed utilization of Lates calcarifer. The second degree polynomial regression indicates that fed three times a day is optimum for best growth performance and survival for Asian sea bass.     

Survival,growth and physiological responses of juvenile Japanese flounder (Paralichthys olivaceus,Temminck & Schlegel, 1846) exposed to different dissolved oxygen concentrations and stocking densities

The aim of this study was to determine to what extent juvenile Japanese flounder can adapt to different stocking densities in captivity and to examine whether growth and some physiological parameters critical for welfare might be affected by different dissolved oxygen levels. Japanese flounder (Paralichthys olivaceus) juveniles (initial weight 1.27 ± 0.04 g/fish) were reared at five stocking densities (500, 1,000, 1,500, 2,000, 2,500 ind/m³) and two levels of dissolved oxygen (DO) concentration (5.5 ± 0.5 mg/L or 14 ± 2 mg/L) with duplicate tanks for each treatment in water‐recirculating systems for 40 days. Survival and activity of superoxide dismutase (SOD) were not affected either by stocking density or dissolved oxygen, whereas final body weight, specific growth rate (SGR) and feed conversion efficiency (FCE) of fish under low DO concentration decreased significantly with increasing stocking density. In contrast, growth of fish reared in high DO levels were unaffected by the stocking density. Furthermore, fish in this group had a higher feed intake and, consequently, grew faster (SGR) and achieved a higher final weight than fish reared at the low DO level. A significant reduction in hemoglobin (Hb) concentration and red blood cell (RBC) count of fish were recorded as DO concentration increased. Furthermore, the activity of protease decreased significantly with increasing stocking density and increased significantly with increasing DO concentration. The ventilation frequency results indicate that gill ventilation decreased significantly as DO levels increased. This study demonstrates that stocking density can affect the growth performance and physiological parameters critical for welfare of juvenile Japanese flounder. Also shown is that pure oxygen supplementation is an effective way to improve the growth of juvenile Japanese flounder when reared at a high stocking density.     

Prey availability and selective feeding of sea trout (Salmo trutta L., 1758) fry stocked in small forest streams

The food base and stomach contents of stocked sea trout (Salmo trutta) fry were determined in the first 4 months (April–August 2010) of life in two small lowland streams after resorption of the yolk sac. In each stream, 600 individual trout were released in a 200 m stocking‐section. The macrozoobenthos given as a food base for the fry were collected once a month from the streams using a bottom scraper. Three subsamples of macrozoobentos were considered as one sample from the stocking‐section. On the same day, 50 stocked fry were captured in each stream using electric fishing gear. Preferred food components were usually the taxa represented by number in a given stream in a particular month. Width size range of the prey in fish stomachs in May was from 0.10 to 1.47 mm, and from 0.11 to 3.78 mm in August. All food items found in both streams during the study months were also represented in intensity in the fish: Cyclopoida, and larvae of Baetidae and Chironomidae. Almost all Helodidae and Simuliidae larvae as well as the majority of Limoniidae and Nemouridae larvae were available as food each month.     

Larval rearing of fringe-lipped carp,Labeo fimbriatus (Bloch) with low cost diets including green bottle fly Lucilia sericata (Meigen) larvae meal incorporated diet

A study was conducted with non-conventional ingredients to test their efficacy as fishmeal (FM) replacers in the diet of fringe- lipped carp. Labeo fimbriatus first feeding larvae and fry were reared for 30 and 60 days in indoor, 50 L, aerated, circular plastic tanks at 100 and 30 numbers tank⁻¹, respectively. In the first feeding larvae to fry rearing experiment (Exp. 1), the fish were fed with either of the following isonitrogenous and isocaloric diets – live plankton, FM diet, green bottle fly (Lucilia sericata) larvae meal (GBFLM) diet and silkworm pupa (SWP) diet. The fry to fingerling rearing (Exp. 2), was also conducted using the same diets described above except live plankton. All compounded diets were formulated to contain 40% crude protein for the experiment 1 and 35% for experiment 2 and were fed ad libitum. Triplicate tanks were maintained for each treatment in both the experiments. In Exp. 1, the mean final weight of fry was higher with plankton and FM diets, while no difference (p > .05) was observed between FM and GBFLM diets. Weight of fish fed SWP diets was not statistically different from those fed GBFLM diet. No difference (p > .05) in final length, survival and condition factor was recorded. Analysis of digestive enzyme activity of whole fish revealed lower (p < .05) activity of amylase in fish fed plankton. In Exp. 2, no difference (p > .05) was observed between the different diet groups in terms of mean final weight, length, survival and condition factor. Analysis of digestive enzyme activity of whole fish revealed no difference (p > .05) in the activity of digestive enzymes between the treatments except a lower (p < .05) activity of trypsin in FM diet and lipase in FM and GBFLM diets. Since the survival and condition factors of animals is the most important aspect during nursery rearing, similar (p > .05) values recorded in different treatments indicate the possibility of incorporation of these non-conventional protein sources in the diet of L. fimbriatus during first feeding larvae to fry and fry to fingerling rearing.     

Dietary supplementation of fructooligosaccharide (FOS) improves the innate immune response, stress resistance, digestive enzyme activities and growth performance of Caspian roach (Rutilus rutilus) fry

The present study investigated the effects of prebiotic fructooligosaccharide (FOS) on the innate immune response, stress resistance, digestive enzyme activities, growth factors and survival of Caspian Roach (Rutilus rutilus) fry. After acclimation, fish (0.67 ± 0.03 g) were allocated into 12 tanks (50 fish per tank) and triplicate groups were fed a control diet or diets containing 1%, 2% or 3% FOS. At the end of the trial (7 weeks), humoral innate immune parameters (serum Ig levels, lysozyme activity and alternative complement activity (ACH50)), resistance to salinity stress (150 g L⁻¹), digestive enzyme activities (amylase, lipase and protease) and growth factors (final weight, weight gain, specific growth rate (SGR), food conversion ratio (FCR), and condition factor) were assessed. At the end of the study the innate immune responses (Ig levels, lysozyme activity and ACH50) were significantly higher in 2% and 3% FOS fed fish (P < 0.05), whereas, 1% dietary FOS only elevated serum lysozyme activity. All dietary FOS levels significantly increased resistance to a salinity stress challenge (P < 0.05) and highest survival was observed in the 3% FOS group. Similarly, digestive enzyme activities were significantly elevated with increasing levels of dietary FOS (P < 0.05). Subsequently, elevated growth performance (final weight, SGR and FCR) was observed in roach fed 2% and 3% FOS compared to the control group (P < 0.05). These results indicate that FOS can be considered as a beneficial dietary supplement for improving the immune response, stress resistance, digestive enzyme activities and growth performance of Caspian roach fry.     

Cold storage effects on flesh quality of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) fed diets containing different vegetable oils

The intention of this experiment was to assess the effects of different sources of dietary lipid on the fatty acid composition of the fillet and liver and the flesh quality traits of rainbow trout (Oncorhynchus mykiss) after a 70‐day feeding period. Four iso‐nitrogenous (approx. 51% crude protein) and iso‐lipidic (approx. 14% crude lipid) experimental diets were formulated. The control diet contained only fish oil (FO) as the primary lipid source. In the other three dietary treatments, fish oil was replaced by 100% (LO30/SO35/SFO35) and 70% (FO30/LO35/SO35 or FO30/SO35/SFO35) sesame oil (SO), linseed oil (LO), or sunflower oil (SFO). Triplicate groups of 40 rainbow trout (~46 g) held under similar culture conditions were hand‐fed daily to apparent satiation for 70 days. At the end of the feeding trials, no difference in growth performance among experimental groups was noted (P > 0.05). There were some differences in the proximate composition of fish fillets (P < 0.05): the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels were highest in fish fed the control diet (P < 0.05); and EPA and DHA levels in fish fed the FO30/LO35/SO35 diet were closest to the control diet (P < 0.05). In contrast, fish fed the diet containing 100% plant oils (LO30/SO35/SFO35) had the highest level of total n‐6 fatty acids in the fillet and liver. In a 12‐day refrigerated storage at 1°C the thiobarbituric acid (TBA), trimethylamin nitrogen (TMA‐N) and pH values gradually increased in all dietary groups (P < 0.05). The chemical indicators of spoilage, TBA, TMA‐N, and pH values were within the limit of acceptability for human consumption.     

Effect of stocking density on growth and survival of Clarias batrachus (Linn.) larvae and fry during hatchery rearing

Experiments were conducted to determine optimum stocking density for Clarias batrachus larvae and fry during hatchery rearing. The increase in stocking density decreased the total weight, specific growth rate (SGR) and percent weight gain of Clarias larvae during a 13‐day experiment. Survival rate was highest at a stocking density of 1000 m^?2 and lowest at 5000 m^?2. Stocking density did not influence the total biomass production of larvae. Clarias batrachus fry performance was studied during a 28‐day hatchery rearing experiment whereby fry stocked at a density of 100 m^?2 attained the highest total body weight (P < 0.05). The survival rate greatly declined to 59–61% by a density increase to 300 m^?2 and above. Stocking density influenced growth and survival of C. batrachus larvae and fry during hatchery rearing. The best performance was obtained when larvae were stocked at 2000 m^?2; survival was highest with C. batrachus fry stocked at 200 m^?2.     

Stocking experiment with Atlantic salmon and sea trout parr reared on either live prey or a pellet diet

Survival rate and growth parameters of Atlantic salmon fry and sea trout fry were determined after stocking in the wild. Before release (22 May 2009) into the wild the larvae were reared for 10 weeks in the hatchery in three groups: (i) fry fed on live zooplankton , (ii) fry fed on larvae of live nekton, and (iii) fry fed on prepared pellet food. In autumn (15 September 2010) the fish were caught in the wild; the survival rate and growth parameters of both Atlantic salmon and sea trout were the highest in the zooplankton‐fed group, whilst the pellet‐fed group had the lowest survival rate and growth value parameters. Most effective food for hatchery‐reared fishes to be used as stock was the natural living zooplankton. The general conclusion is that the live diet supplied in the rearing period has a positively impact on fish survival in the wild.     

Phytase can reduce theneedfor monocalcium phosphate supplementation in soybean and rapeseed meal‐based diets of black sea bream,Acanthopagrus schlegelii (Bleeker, 1854)

A feeding trial was conducted to study the effect of partial replacement of dietary monocalcium phosphate (MCP) with phytase on growth performance, feed utilization and phosphorus discharge in black sea bream, Acanthopagrus schlegelii. In the feeding trial, the control diet (designated as P1.5) was prepared with 1.5% MCP but without phytase, and the three other diets (designated as PP1.0, PP0.5 and PP0, respectively) were supplemented with 1.0%, 0.5% and 0% MCP, respectively, along with 200 mg (400 U) phytase/kg diet in each. Each diet was tested in triplicate tanks and fish were fed twice daily to satiation. After an 8‐week feeding trial in indoor flow‐through cylindrical fibreglass tanks (25 fish per tank, initial body weight: 11.5 ± 0.12 g), fish fed with PP1.0 and PP0.5 had no significant change in weight gain (WG), specific growth rate (SGR), protein efficiency rate (PER) or feed conversion ratio (FCR) compared to the control (p > .05), whereas fish fed with PP0 showed a significantly lower growth performance in the above parameters (p < .05). The addition of phytase did not affect the body composition or muscle composition. The apparent digestibility coefficients (ADCs) of crude protein and phosphorus increased when fish were fed diets in which MCP was replaced by phytase. Phosphorus discharge was also significantly reduced in fish fed diets in which MCP was replaced by phytase (10.2 ± 0.50 to 8.01 ± 0.47 g/kg weight gain). The present study suggests that dietary MCP can be reduced when phytase is added to the black sea bream diet, with a maximum MCP reduction level of up to 1% when phytase is supplemented at 200 mg (400 U)/kg diet. Thus, phytase in the diet of black sea bream is economically and ecologically beneficial.     

Growth performance of juvenile Russian sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) at two stocking densities in net cages

The growth performance of juvenile sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) was studied in experimental net cages (2 m × 2 m × 2 m) in freshwater Sapanca Lake. Fertilized eggs were imported from Krasnodar, Russia in January 2001. Two experimental stocking densities were employed (12 and 8 ind. m⁻³). Sturgeon were hand‐fed a pelleted commercial trout feed twice daily throughout the 203‐day experiment period. Fish were grown at ambient temperature (12.7–28.5°C) and natural photoperiod. Initial and final mean body weights were 279.5 g (±31.27) and 1112.8 g (±234.77) in the first group, and 271.1 g (±28.21) and 1140.5 g (±213.31) in the second group, respectively. Results were a fourfold biomass density increase in both trials from an initial 3.48 to 12.4 kg m⁻³ (high density) and 2.2 to 8.8 kg m⁻³ (low density). Mean specific growth rate (SGR) was determined as 2.69% day⁻¹ in both groups. Mean condition factor (CF) at the end of the experiment was 0.36 ± 0.05 in the high‐density group and 0.41 ± 0.05 in the low‐density group. Mean feed conversion ratio (FCR) was calculated to be 5.7 and 5.8, respectively. Survival was 92.7% in the first group (high density) and 96.1% in the second group (low density). The results demonstrated that sturgeon juveniles can be raised in cages and that growth performance (CF, SGR and FCR) and mortality of sturgeon were not significantly different at the two stocking densities (P > 0.05) tested.     

Effects of stocking density on survival,growth and size variation of juvenile Brachymystax lenok (Pallas, 1773)

In this experiment the effects of stocking density on growth and survival of juvenile Brachymystax lenok were studied. Experimental fishes were reared at different stocking densities (5, 25, 50 and 75 fish L^?1) for 40 days at ambient temperatures (11.2–16.4°C). During the experiment, dissolved oxygen (DO) was above 5.4 mg L^?1 and other major environmental factors were controlled at the same levels in each aquarium (DO 5.4–7.2 mg L^?1, pH 6.6–7.4, and flow‐through rates 0.3–0.4 L s^?1). Mortality data in each group was recorded daily and random samples of 30 juveniles were measured and weighed every 10 days. All statistical analyses were performed by anova . The survival rate was found to be significantly affected by stocking density, but not the condition factor (CF), specific growth rate (SGR) or coefficients of variation (CV).The results demonstrate that lenok juveniles can be reared at higher stocking densities, which can increase survival under intensive conditions.     

Stressor interactions in freshwater habitats: Effects of cold water exposure and food limitation on early‐life growth and upper thermal tolerance in white sturgeon,Acipenser transmontanus

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Effects of sustained predation by fast‐growing transgenic common carp (Cyprinus carpio Linnaeus, 1758) on gastropods in artificial environments

The present study addressed the effects of growth hormone‐transgenic and non‐transgenic common carp (Cyprinus carpio L.) predation on the community and populations of four gastropod species cultured in artificial environments. After a 110‐day population‐based predation experiment (three replicate pools [16 m²] for each genotype with one fish [total length 45.0~51.4 cm] and 150 Bellamya aeruginosa (Reeve 1863) per pool), there were no significant effects of predation by either transgenic or non‐transgenic carp on the biomass, number, or size selectivity of the population. Following a 10‐day community‐based predation experiment (three replicate pools [16 m²] for each genotype with one fish [total length 45.0~50.5 cm] and 150 Alocinma longicornis (Benson 1842), 100 Parafossarulus sinensis (Neunayr 1883), 55 B. aeruginosa, and 33 Radix auricularia L. per pool), the consumption rate and the number of gastropods predated by transgenic carp were 2.60 times and 2.85 times higher, respectively, than those of non‐transgenic carp. Furthermore, the biomass of A. longicornis, P. sinensis and B. aeruginosa consumed by transgenic carp was significantly (p < .05) higher than that by non‐transgenic carp. There was a significant difference in the type selection of the four gastropods by the transgenic and non‐transgenic carp, but both predators preferred R. auricularia and avoided B. aeruginosa. Compared with the non‐transgenic carp, predation by transgenic carp resulted in a significant decrease in A. longicornis (p < .05) and an increase in B. aeruginosa (p < .05). These results indicate that the effects of predation by both transgenic and non‐transgenic carp on the B. aeruginosa population tend to be similar, but their effects on the community composed of the four gastropods were significant different. This information may be useful for assessing the environmental risk of transgenic carp.     

The effects of water temperature and ration size on growth and body composition of fry of common carp, Cyprinus carpio

Experiment was conducted with the aim of determining the effect of varying water temperature and ration size on growth and body composition of fry of the common carp, Cyprinus carpio. Common carp fry with an initial body weight (BW) of 0.86 g were fed a diet (34.9% protein, 18.3 KJ/g diet) at four ration sizes 4%, 5%, 6% and 7% of their body weight per day and reared at two water temperatures 28 and 32 °C for 60 days. Fry fed with 6% ration showed the highest mean final body weight at 28 °C. Final body weight was significantly (P<0.05) affected by ration and temperature. Cyprinus carpio fry raised at 28 °C had higher feed efficiency (FE) (44.36%) than the fry reared at 32 °C (40.98%) with 4% ration. Further, feed efficiency decreased with increase in ration levels in both temperatures. Protein efficiency ratio (PER) was higher (1.26) at 28 °C than at 32 °C (1.17). At 6% ration, common carp fry showed highest specific growth rate (SGR) (3.82%/day) at 28 °C as compared with at 32 °C (3.57%/day). A linear increase in protein and lipid contents was evident with increasing ration levels up to 6% body weight at both temperatures 28 and 32 °C. Second-order polynomial regression analysis of weight gain and SGR indicated the breakpoints at ration level 6.04% and 6.08% body weight per day at 28 and 32 °C. Hepatosomatic index (HSI) not affected by temperature and ration size while, viscerosomatic index (VSI) influenced (P<0.05) by ration size and temperature. Based on the above results, it may be concluded that 6% BW/day ration is optimal for growth of Cyprinus carpio fry at both the temperatures 28 and 32 °C.     

High stocking density during larviculture and effect of size and diet on production of juvenile Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae)

Different stocking densities were investigated in larviculture and feeding of Lophiosilurus alexandri, as well as analyses of the effects on juveniles of two size‐classes and two different commercial formulated diets. The first experiment was two‐phased: (a) larvae stocked at densities of 60, 120, 180, 240, and 300 larvae L⁻¹ fed with Artemia nauplii and reared for 15 days; (b) in phase 2, densities of 5, 10, 15, 30, and 40 juveniles L⁻¹ were evaluated during feed training (20 days). Mean water temperature in both phases was 28°C. In the first phase of experiment 1, the different stocking densities did not affect fish growth or survival. In phase 2, growth was similar in all densities; however, survival was lower at higher densities. The increased density provided a rise in biomass and number of individuals produced in both phases. In the second experiment, two size‐classes of feed‐trained juveniles (30.22 ± 1.84 and 34.66 ± 2.41 mm) were given pellets of two different diameters (1.2 and 2.6 mm) for 20 days. The largest juveniles fed the 1.2 mm inert diet had higher final weights and lengths. Larviculture and feed training of L. alexandri can thus be performed successfully at high stocking densities of 300 larvae L⁻¹ during the first 15 days of feeding, and at densities of up to 40 juveniles L⁻¹ during the 20 days of feed training, respectively.     

Effect of dietary carbohydrate on the growth performance,immune response,hepatic antioxidant abilities and heat shock protein 70 expression of Wuchang bream,Megalobrama amblycephala

To investigate the effects of different carbohydrate (CHO) levels in the diet of Wuchang bream Megalobrama amblycephala, the fish were randomly divided into six treatment groups. Five groups were fed 19, 25, 31, 38 and 47% CHO, respectively, for 8 weeks, and a control group was fed a diet with no CHO. Growth performance and feed utilization were significantly (P < 0.05) affected by the dietary carbohydrate level. Maximum weight gain and specific growth rate occurred at the 31% dietary carbohydrate level. Compared to the control, the 31% CHO group had a significantly increased serum total protein content, respiratory burst activity of leucocytes, serum complement 3 (C3) levels, serum lysozyme activity, serum alkaline phosphatase (AKP) activity and hepatic total antioxidative capacity (T‐AOC), as well as a decrease in serum glutamic‐oxaloacetic transaminase (GOT) activity. Compared to the control, the 47% CHO group had significantly increased serum GOT activity, and a tendency toward an increase in serum cortisol content and a decrease in serum lysozyme activity, hepatic superoxide dismutase (SOD) activity and T‐AOC. The relative level of hepatic heat shock protein 70 (HSP70) mRNA in fish fed the 38% CHO diet was significantly higher than those of fish fed the 19, 25 and 31% CHO diets, respectively (P < 0.05). After challenge with Aeromonas hydrophila, fish fed the 47% CHO had the significantly lowest post‐challenge survival, and fish fed the 31% CHO had the significantly highest post‐challenge survival (P < 0.05). The results of this study suggest that ingestion of excessive dietary CHO can impact the non‐specific immune responses, decrease the hepatic antioxidant abilities, and thus affect the health status of M. amblycephala.