Susceptibility of Nile tilapia (Oreochromis niloticus) fed with dietary sodium chloride to nitrite toxicity

Juvenile Nile tilapia (Oreochromis niloticus) were fed with diets supplemented with 0 or 6% NaCl for 10 weeks. Tilapia were exposed to approximately 21 mg/l nitrite-N after 5 and 10 weeks of feeding to determine the effect of dietary NaCl supplementation on resistance to nitrite toxicity. Fish were sampled before (baseline, pre-exposure) and after 24 h nitrite exposure to determine the effects of dietary NaCl on mortality, hematology (hematocrit, hemoglobin, and methemoglobin), and plasma electrolyte dynamics (nitrite, chloride, sodium, and potassium). After 10 weeks of feeding, tilapia were also challenged with Streptococcus iniae to determine the effect of sodium chloride on immunity. Tilapia fed with the NaCl-supplemented diet had significantly higher weight gain compared with the control group, which was associated with a significant increase in feed intake in the NaCl group. Mortality from nitrite exposure was lower in tilapia fed with the NaCl-supplemented diet compared with the control group at 5 and 10 weeks, but the differences were not significant. However, dietary NaCl supplementation caused a significant decrease in plasma nitrite levels after nitrite exposure. The dietary reduction in nitrite may be related to the increase in plasma chloride in the 6% NaCl-supplemented fish. A direct link between the effects of dietary NaCl supplementation on methemoglobin (MetHb) could not be established. Tilapia in this study were subjected to acute nitrite toxicity. Dietary sodium chloride may be more effective in protecting against nitrite toxicity at lower levels of nitrite, but the conditions at which it proves to be effective may be limited and requires further investigation. Feeding NaCl to tilapia did not affect susceptibility to S. iniae or immune function, but nitrite exposure cause a stress-related reduction in non-specific immune function. This is the first study to examine the effects of dietary salt on nitrite toxicity in tilapia.     

Effect of dietary calcium on growth and survival of silver catfish fingerlings, Rhamdia quelen (Heptapteridae), exposed to different water pH

The purpose of this study was to verify the effect of dietary Ca²⁺ on the growth and survival of silver catfish fingerlings (Rhamdia quelen) exposed to different water pH (5.5, 7.5 and 9.0). Silver catfish fingerlings were randomly placed in a thermoregulated water re‐use system with twelve 250 L‐tanks, two 1000 L‐biofilters and a 2000 L‐reservoir with a medium flow of 3.84 L min^?1 tank. Stocking density was 0.16 fingerlings L^?1. To prepare the treatment diets, the control diet (0.8 g kg^?1 Ca²⁺) was supplemented with CaCO₃ to yield experimental diets with 6.4, 9.5 and 23.9 g kg^?1 Ca²⁺. There were three replicates/treatments. Survival was more than 93.9% in all treatments. Exposure of silver catfish fingerlings to alkaline or acid water reduced growth, and this effect was not ameliorated by dietary Ca²⁺ supplementation. Moreover, when fingerlings were maintained in water with pH 7.5, the best dietary Ca²⁺ range for silver catfish fingerling growth was 0.8–6.4 g kg^?1.     

Comparative study on the effect of dietary lipid level on growth and feed utilization for gibel carp (Carassius auratus gibelio) and Chinese longsnout catfish (Leiocassis longirostris Günther)

An 8‐week growth trial investigated the effect of dietary lipid level on growth performance of a carnivorous fish, Chinese longsnout catfish (Leiocassis longirostris Günther) and an omnivorous fish, gibel carp (Carassius auratus gibelio). For each species, seven isonitrogenous semi‐purified diets (455 g kg^?1 crude protein for Chinese longsnout catfish and 385 g kg^?1 crude protein for gibel carp) were formulated to contain 30, 60, 90, 120, 150, 180 or 210 g kg^?1 lipid. For Chinese longsnout catfish, feed intake (FI) decreased with increasing dietary lipid and there was no significant difference in feed intake from 90 to 210 g kg^?1 lipid. Specific growth rate (SGR) increased with dietary lipid level (P < 0.05) and the 150 and 180 g kg^?1 groups were the best. Feed conversion efficiency (FCE), protein retention efficiency (PRE) and energy retention efficiency (ERE) were higher at 180 g kg^?1 lipid. For gibel carp, FI decreased with increased dietary lipid and 180 and 210 g kg^?1 lipid groups showed lower values. SGR increased with dietary lipid level and the 150 and 180 g kg^?1 were the best. FCE was higher at 180 g kg^?1 lipid level. PRE increased with dietary lipid level and there was no significant difference in groups from 120 to 210 g kg^?1 dietary lipid. ERE increased with increasing dietary lipid level, and groups fed 120, 150 and 180 g kg^?1 lipid showed the highest values. In Chinese longsnout catfish, increase in dietary lipid level, resulted in increased carcass dry matter, crude protein, crude lipid and gross energy. In gibel carp, dry matter, crude protein, and crude lipid increased with dietary lipid level. Based on regression between SGR and dietary lipid, dietary lipid requirements for Chinese longsnout catfish and gibel carp were 142.6 and 140.5 g kg^?1, respectively.     

Nutriphysiological and cytological responses of juvenile channel catfish (Ictalurus punctatus) to dietary oxidized fish oil

An 86‐day growth trial was conducted to investigate the effect of dietary oxidized fish oil on the growth and cytopathology of juvenile channel catfish (Ictalurus punctatus). Four diets containing 0 g kg^?1 (control: fresh fish oil), 30 g kg^?1 (low‐oxidized oil group), 60 g kg^?1 (medium‐oxidized oil group) and 90 g kg^?1 (high‐oxidized oil group) graded oxidized oil levels with the same dietary lipid level (90 g kg^?1 diet) were evaluated. The results show that the specific growth rate decreased with increasing dietary oxidized oil level (P < 0.05). All examined liver and kidney tissues in all dose groups exhibited what appeared as dose‐dependent cellular modifications. In addition, lipid droplet accumulation in the hepatocytes of fish in all dose groups was increased, and their localizations were distinctly different between all dose groups. The ultrastructural changes suggest the progression of mitochondrial vacuolation, especially in the renal tubules, in all dose groups. These results reveal a previously underappreciated effect of dietary oxidized fish oil on channel catfish kidneys. Overall, a series of nutriphysiological responses were adversely affected by exposure to dietary oxidized fish oil, and the corresponding interference patterns on the metabolism and transport of nutrients within cells were observed.     

Acute toxicity of nitrite on white shrimp Litopenaeus vannamei (Boone) juveniles in low‐salinity water

The nitrite toxicity was estimated in juveniles of L. vannamei. The 24, 48, 72 and 96 h LC₅₀ of nitrite‐N on juveniles were 8.1, 7.9, 6.8 and 5.7 mg L^?1 at 0.6 g L^?1; 14.4, 9.6 8.3 and 7.0 mg L^?1 at 1.0 g L^?1; 19.4, 15.4, 13.4 and 12.4 mg L^?1 at 2.0 g L^?1 of salinity respectively. The tolerance of juveniles to nitrite decreased at 96 h of exposure by 18.6% and 54.0%, when salinity declined from 1.0 to 0.6 g L^?1 and from 2.0 to 0.6 g L^?1 respectively. The safe concentrations at salinities of 0.6, 1.0 and 2.0 g L^?1 were 0.28, 0.35 and 0.62 mg L^?1 nitrite‐N respectively. The relationship between LC₅₀ (mg L^?1), salinity (S) (g L^?1) and exposure time (T) (h) was LC₅₀ = 8.4688 + 5.6764S – 0.0762T for salinities from 0.6 to 2.0 g L^?1 and for exposure times from 24 to 96 h; the relationship between survival (%) and nitrite‐N concentration (C) for salinity of 0.6–2.0 g L^?1, nitrite‐N concentrations of 0–40 mg L^?1 and exposure times from 0 to 96 h was as follows: survival (%) = 0.8442 + 0.1909S – 0.0038T – 0.0277C + 0.0008ST + 0.0001CT–0.0029SC, and the tentative equation for predicting the 96‐h LC₅₀ to salinities from 0.6 to 35 g L^?1 in L. vannamei juveniles (3.9–4.4 g) was 96‐h LC₅₀ = 0.2127 S² + 1.558S + 5.9868. For nitrite toxicity, it is shown that a small change in salinity of waters from 2.0 to 0.6 g L^?1 is more critical for L. vannamei than when wider differences in salinity occur in brackish and marine waters (15–35 g L^?1).     

A study on dietary l‐lysine requirement of juvenile yellow catfish Pelteobagrus fulvidraco

An 8‐week feeding trial was conducted to determine lysine requirement of juvenile yellow catfish (Pelteobagrus fulvidraco) by feeding formulated diets containing crystalline l ‐lysine. Six isonitrogenous and isoenergetic diets (405 g kg^?1 protein, 18 kJ g^?1 gloss energy) containing fish meal together with soybean protein concentrate as protein sources and fish oil together with soybean oil as lipid sources were formulated. Crystalline l ‐lysine was added into the six diets to acquire lysine concentrations of 17.3, 21.8, 26.0, 31.3, 35.5 and 41.9 g kg^?1 dry diets, respectively. Mixture of crystalline amino acid was supplemented to simulate the amino acid profile in muscle of yellow catfish. The results indicated that final body weight (FBW), weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency (PE) increased with the increase in dietary lysine level from 17.3 to 31.3 g kg^?1 of diet and then decreased as the dietary lysine levels further increased. No significant difference in survival rate was found among all the dietary treatments. One‐slope, quadratic broken‐line analysis on the basis of SGR showed that the dietary l ‐lysine requirement of juvenile yellow catfish was 33.1 g kg^?1 of dry diet (83.2 g kg^?1 of dietary protein).     

Effect of chloride on nitrite‐induced methaemoglobinemia in Atlantic sturgeon,Acipenser oxyrinchus oxyrinchus (Mitchill)

We evaluated the effects of chloride concentration on the clinical pathology in juvenile Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus (Mitchill), following semi‐static exposures to 1 mg L^?1 nitrite for 96 h. In spring water naturally low in chloride (5 mg L^?1), plasma nitrite concentrated to more than 40× environmental levels resulting in a severe methaemoglobinemia characterized by torpid behaviour, 30‐fold increase in methaemoglobin fraction, anaemia, leucopenia and hyperkalaemia. Loss of intracellular water and potassium to extracellular space may have resulted in hyperkalaemia and haemodilution. Fish survived nitrite exposure, but 60% of torpid fish died following capture and tissue sampling. Fish acclimated to 10‐fold higher chloride content (55 mg L^?1) did not concentrate nitrite in the plasma above environmental levels or develop methaemoglobinemia, but did exhibit similar haematology and plasma chemistry changes. Plasma nitrite returned to preexposure levels by 14 days following nitrite exposures, but severity of clinical pathology changes persisted or increased, suggesting that Atlantic sturgeon have reduced capacity to recover from methaemoglobinemia. Fish that survive methaemoglobinemia may be susceptible to mortality from the cumulative effects of intoxication, handling and other stresses for two or more weeks following nitrite remediation. Chloride buffering in aquaculture systems reduces the toxic effects of nitrite accumulation.     

Effect of natural free gossypol and gossypol‐acetic acid on growth performance and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge

A study was conducted to evaluate the effect of free gossypol from glanded‐cottonseed meal (G‐CSM) (natural free gossypol) or gossypol‐acetic acid on growth performance, body composition, haematology, immune response and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge. Soya bean meal‐based diets supplemented with 0, 100, 200, 400, and 800 mg kg^?1 free gossypol from G‐CSM or gossypol‐acetic acid were fed to juvenile channel catfish in triplicate aquaria to apparent satiation twice daily for 12 weeks. Neither sources nor levels of dietary gossypol significantly influenced the final weight gain, feed intake, feed efficiency and survival of channel catfish. Similarly, whole‐body proximate composition, haematological parameters (red blood cell, white blood cell counts, haemoglobin and haematocrit), serum protein concentration, macrophage chemotaxis ratio, phagocytic activity and antibody production against E. ictaluri 21‐day postinfection were not significantly affected at either dietary sources or levels of gossypol. Gossypol concentrations of liver were linearly related to dietary level of gossypol but the retention rate varied dependent on sources of the dietary gossypol. At dietary gossypol levels of 400 or 800 mg kg^?1, total gossypol concentrations in liver of fish fed dietary gossypol from G‐CSM were significantly higher than those of fish fed the corresponding levels of gossypol from gossypol‐acetic acid. The (+)‐isomer of gossypol was predominantly retained in liver regardless of dietary sources of gossypol. The ratio of (+) to (?) gossypol isomers in liver decreased with increasing dietary concentrations of gossypol. Serum lysozyme activity of fish fed dietary gossypol levels of 200 mg kg^?1 or higher, either from G‐CSM or gossypol‐acetic acid, was significantly higher than that of the control. At a level of 800 mg kg^?1 diet, gossypol from G‐CSM stimulated significantly higher lysozyme activity than gossypol from gossypol‐acetic acid. Fish fed diets containing 400 mg kg^?1 gossypol or higher from G‐CSM or 800 mg kg^?1 gossypol from gossypol‐acetic acid had significantly increased superoxide anion (O) production. However, neither the sources nor the levels of dietary free gossypol influenced the resistance of juvenile channel catfish to E. ictaluri challenge.     

Effects of 7,12-dimethylbenz(a)anthracene on growth and haematological parameters in Korean rockfish, Sebastes schlegeli (Hilgendorf)

The objectives of the present experiment were to determine the effects on growth factors and some haematological parameters in Korean rockfish, Sebastes schlegeil, after dietary 7,12‐dimethylbenz(a)anthracene (DMBA) exposure at 0.6, 1.2, 2.4 and 4.8 mg kg^?1 diet for 8 weeks. The specific growth rate of the fish exposed to DMBA (≥1.2 mg kg^?1) showed significantly lower performance than the control. Following 8 weeks of exposure, the DMBA‐exposed groups (2.4 and 4.8 mg kg^?1) had a significantly higher mean hepatosomatic index. Condition factor of the fish exposed to DMBA did not show any statistically significant deviation from the control (P>0.05), although the mean values were somewhat lower than those of the control group. Observations on haematological parameters indicated DMBA treatment induced a severe anaemia. Total protein, albumin and total cholesterol concentrations decreased following exposure to DMBA at 2.4 and 4.8 mg kg^?1. In contrast, serum bilirubin and blood urea nitrogen in fish exposed to DMBA increased. Significant decreases in serum electrolytes, chloride, phosphorus, magnesium and calcium, and osmolality were observed in all DMBA‐treatment groups. All DMBA‐treatment groups showed a significantly higher activity of lactate dehydrogenase and alkaline phosphatase. Serum transaminase activity after the highest level of 4.8 mg kg^?1 DMBA was significantly increased. The key finding from this study is that rockfish exposed to dietary DMBA at concentrations of 1.2 and 2.4 mg kg^?1 diet are likely to experience adverse impacts in growth and haematological property respectively.     

The growth performance of southern catfish fed diets with raw, precooked cornstarch and glucose at two levels

The ability of juvenile carnivorous southern catfish (Silurus meridionalis Chen) to use different levels, kinds and physic state (glucose, raw cornstarch and precooked cornstarch) of dietary carbohydrate was evaluated in term of growth performance. All diets contained 100 g kg^?1 lipid and 16 kJ metabolizable energy. Three isonitrogeneus (400 g kg^?1) diets were formulated to contain 150 g kg^?1 raw cornstarch, precooked cornstarch and glucose. Another three isonitrogeneus (300 g kg^?1) diets were formulated to contain 300 g kg^?1 raw cornstarch, precooked cornstarch and glucose. A control diet was formulated with no carbohydrate containing 500 g kg^?1 protein. Each experimental diet was fed to four tanks of 10 fish (28.3 ± 0.5 g) for 8 weeks at 27.5 °C. Specific growth rate (SGR) of 300 g kg^?1 glucose diet was significantly lower than those of other diets (P < 0.05). Feeding rates (FR) of 300 g kg^?1 glucose and control diets were significantly lower than those of the other diets (P < 0.05). Feed efficiency (FE) was significantly decreased with increased dietary carbohydrate level (P < 0.05). Feed efficiency of the 300 g kg^?1 glucose diet was significantly lower than those of the 300 g kg^?1 raw and precooked cornstarch diets (P < 0.05). The protein efficiency ratio (PER) was significantly increased with dietary carbohydrate level except that of the 300 g kg^?1 glucose diet, which was lowest among all diets (P < 0.05). The results suggested that both dietary starch and glucose were utilized for energy in southern catfish and had a protein‐sparing effect. At 150 g kg^?1 inclusion level, the utilization of raw and precooked cornstarch and glucose did not vary significantly, but a higher dietary glucose level (300 g kg^?1) had a markedly detrimental effect on growth in southern catfish.     

The effects of vitamins C and E on the growth,tissue accumulation and prophylactic response to thermal and acidic stress of hybrid catfish

This study investigated the effects of the co‐supplementation of vitamins C (0, 500, and 1000 mg kg^?1) and E (0, 62.5, and 125 mg kg^?1) on the growth performance, haematology and the modulation of blood stress indicators and immune parameters in hybrid catfish (Clarias macrocephalus × Clarias gariepinus) under combinations of thermal and acidic stress. Supplementation of vitamins C and E influenced the growth, haematological indices, serum chloride, plasma protein and immune parameters (lysozyme, total immunoglobulin and alternative complement haemolytic assay) (P < 0.05). Although vitamins C and E did not prevent a significant reduction in serum chloride, they minimized not only the modulation of blood glucose and plasma protein, but also the reduction in immune parameters (P < 0.05) owing to stress. Our results demonstrated that co‐supplementation of 500 mg kg^?1 vitamin C and 125 mg kg^?1 vitamin E, or 1000 mg kg^?1 vitamin C alone, for four weeks and co‐supplementation of both vitamins at low levels (vitamins C at 500 mg kg^?1 and E at 62.5 mg kg^?1) for eight weeks had beneficial effects on the growth, amelioration of stress‐mediated adverse changes in the physiological and immunosuppressive responses of hybrid catfish under stressful conditions.     

Effect of calcium and magnesium hardness on acute copper toxicity to Indian major carp, Labeo rohita (Hamilton) and catfish, Channa punctatus (Bloch)

Four experiments were conducted to evaluate the effects of calcium and magnesium hardness on the acute toxicity of copper sulphate to Indian major carp, rohu (Labeo rohita, Hamilton) fingerlings and juvenile catfish (Channa punctatus, Bloch) in medium alkalinity experiments. A preliminary bioassay determined the 96 h LC₅₀ of copper sulphate to be 0.56 mg L^?1 for L. rohita fingerlings and 11.78 mg L^?1 for juvenile C. punctatus placed in water with calcium hardness and total alkalinity set at 100 mg L^?1 CaCO₃. In the first experiment, rohu were exposed to 0.56 mg L^?1 copper sulphate in environments where calcium hardness was varied from 50 to 350 mg L^?1 CaCO₃ and total alkalinity was 100 mg L^?1 CaCO₃. As calcium hardness increased, copper‐induced rohu mortalities decreased significantly from 90% at 50 mg L^?1 CaCO₃ to 7% at 350 mg L^?1 CaCO₃. In the second experiment, rohu were exposed to 0.56 mg L^?1 copper sulphate in environments where magnesium hardness was varied from 50 to 350 mg L^?1 CaCO₃ with total alkalinity set at 100 mg L^?1 CaCO₃. Hundred percent mortality was observed in magnesium‐based hardness treatments. In the third experiment, catfish were exposed to 11.78 mg L^?1 copper sulphate in environments where calcium hardness was varied from 50 to 400 mg L^?1 and total alkalinity was 100 mg L^?1 CaCO₃. As calcium hardness increased, copper‐induced catfish mortalities decreased significantly from 90% at 50 mg L^?1 CaCO₃ to 4% at 400 mg L^?1 CaCO₃. In the fourth experiment, catfish were exposed to 11.78 mg L^?1 copper sulphate in environments where magnesium hardness was varied from 50 to 400 mg L^?1 CaCO₃, with total alkalinity set at 100 mg L^?1 CaCO₃. In this case, 100% mortality was also observed in magnesium‐based treatments. Mortality rates in magnesium hardness treatments were consistent with those in the second experiment. These data suggest a calcium‐specific mechanism with respect to acute copper toxicity both in rohu and catfish.     

Supplementation of sodium chloride in diets to improve the meat quality of Pacific white shrimp,Litopenaeus vannamei,reared in low‐salinity water

To investigate the effect of dietary sodium chloride (NaCl) on meat quality of white shrimp (Litopenaeus vannamei) reared in low‐salinity (2 g L^?1) water, shrimp were distributed into four groups (treatments T‐1, T‐2, T‐3 and control) with three replicates. All shrimps were completely randomised stocked into 12 tanks at an initial density of 40 shrimps per tank. Diets for the control, T‐1, T‐2 and T‐3 groups consisted of the basal diet supplemented with 0 g kg^?1, 10 g kg^?1, 20 g kg^?1 and 40 g kg^?1 of NaCl respectively. After 50 days, shrimps in T‐3 showed significantly better (P < 0.05) moisture, crude protein and ash than those of the control and T‐1. Higher muscle Na content was observed (P < 0.05) in T‐3 than that of the control. Significant increases (P < 0.05) in contents of inosinic acid, total free amino acid (TFAA) and essential free amino acid (EFAA) were also found in T‐3. Texture assays showed significant differences (P < 0.05) in hardness, adhesiveness and springiness between group T‐3 as compared with those of T‐1 and control. It indicated that dietary supplementation of NaCl appeared to be a promising practice to improve meat quality of white shrimp reared in low‐salinity waters.     

Haematological and biochemical profiles of carp blood following nitrite exposure at different concentrations of chloride

Haematological parameters of 2‐year‐old carp (Cyprinus carpio L.) were assessed to study the protective effect of chloride on the health of fish exposed to elevated nitrite concentrations. Four groups of carp were exposed to different concentrations of nitrite and chloride for 96 h (group E1: 67 mg L^?1 NO₂^?, 11 mg L^?1 Cl^?; group E2: 67 mg L^?1 NO₂^?, 100 mg L^?1 Cl^?; group E3: 0 mg L^?1 O₂^?, 100 mg L^?1 Cl^? and group C: 0 mg L^?1 NO₂^?, 11 mg L^?1 Cl^?). The main haematological response of carp to an acute exposure to nitrite (group E1) was a significant decrease (P<0.05) in haemoglobin concentrations (53.40±6.61 g L^?1), haematocrit (0.21±0.02 LL^?1), erythrocyte count (1.13±0.12 TL^?1), leucocyte count (7.1±4.19 GL^?1) and lymphocyte count (5.28±2.51 GL^?1), and a significant increase in methaemoglobin concentration (90.50±4.38%, P<0.01) and mean corpuscular haemoglobin concentration (0.27±0.2 LL^?1, P<0.05). At higher chloride concentrations (group E2), a lower nitrite toxicity was observed. In group E2 carp, methaemoglobin made up 38.32±13.30%. Erythrocytes in carp exposed to nitrite showed qualitative changes. Compared with the control group C, group E1 carp showed a significantly higher number (P<0.05) of elongated erythrocytes, with the nucleus located at one cell pole (0.519±0.388 TL^?1). All erythrocytes of group E1 carp had remarkably clear cytoplasms compared with the cytoplasm in the control group C. The biochemical values found were comparable with those found in controls. The main histological lesions were found in the gills of carp exposed to nitrite and consisted of hyperplasia and an elevated number of chloride cells.     

Influence of forage fish and dietary lipid supplements on egg quality and fry production in channel catfish (Ictalurus punctatus) × blue catfish (Ictalurus furcatus) hybridization

Hybrid catfish (channel catfish Ictalurus punctatus × blue catfish Ictalurus furcatus) display characteristics that are favourable to aquaculture production. Low hatch percentages are a principal reason this hybrid is not used widely in the catfish industry. This study was conducted to determine whether additional food source rich in lipids may lead to a higher quality egg production. A 10‐week feed trial was conducted in ponds in Auburn, AL. A total of 219 female Kansas Select channel catfish were stocked into nine ponds, 0.04 ha in size. Three dietary treatments were randomly allocated to the ponds. Diet‐1 was a standard 60 g kg^?1 lipid floating catfish feed. Diet‐2 was the same feed supplemented with forage fish at ～28 kg ha^?1. The third diet was the aforementioned catfish feed topcoated with 20 g kg^?1 lipid [10 g kg^?1 menhaden fish oil, 5 g kg^?1 high docosahexaenoic acid (DHA) oil and 5 g kg^?1 high arachidonic acid oil]. Results indicate that brood fish fed the high lipid diet spawned larger egg masses and had larger eggs both in weight and in diameter, with increased complements of fatty acids such as DHA, eicosapentaenoic acid and total n‐3 fatty acids. The neutral and polar lipid fractions are also presented.     

Effect of high dietary intakes of vitamin E and n-3 HUFA on immune responses and resistance to Edwardsiella tarda challenge in Japanese flounder (Paralichthys olivaceus, Temminck and Schlegel)

A feeding experiment was conducted to investigate the effects of high dietary intake of vitamin E (supplied as dl ‐α‐tocopheryl acetate) and n‐3 highly unsaturated fatty acid (n‐3 HUFA) on the non‐specific immune response and disease resistance in Japanese flounder Paralichthys olivaceus. Nine practical diets were formulated to contain one of three levels of vitamin E namely, 0, 80 or 200 mg kg^?1 (the total α‐tocopherol contents in the diets were 21, 97 and 213 mg kg^?1 based on analysis), and at each vitamin E level with one of three n‐3 HUFA levels i.e. 0.5%, 1.5% or 2.0%. Each diet was randomly assigned to triplicate groups of Japanese flounder (initial body weight: 40.5±1.0 g, mean±SD) in a re‐circulation rearing system. Fish were fed twice daily to apparent satiation at 07:00 and 18:00 hours for 12 weeks. During the experimental period, water temperature was maintained at 18±1°C, salinity 31–35 g L^?1, and pH 7.8–8.2. Dissolved oxygen was not less than 6 mg L^?1, and there were negligible levels of free ammonia and nitrite. The results showed that the increase in dietary n‐3 HUFA from 0.5% to 1.0% significantly decreased muscle α‐tocopherol contents in fish‐fed diets with 21 and 97 mg α‐tocopherol kg^?1 diet (P<0.05). In 1.0% HUFA groups, alternative complement pathway activity (ACH₅₀) of fish fed the diet containing the 213 mg α‐tocopherol kg^?1 diet was significantly higher than noted for fish fed the diet containing 97 mg α‐tocopherol kg^?1 diet (P<0.05). Fish fed the diet with 213 mg α‐tocopherol kg^?1 and 2.0% n‐3 HUFA had the highest lysozyme activity (131.7 U mL^?1) among all the dietary treatments. Fish fed the diets containing 97 and 213 mg α‐tocopherol kg^?1 with 1.0% n‐3 HUFA had significantly higher respiratory burst activity than those fed the diets containing 21 mg α‐tocopherol kg^?1 with 0.5 and 1.0% n‐3 HUFA (P<0.05). In the disease resistance experiment, high intake of dietary vitamin E with 213 mg α‐tocopherol kg^?1 significantly decreased cumulative mortality and delayed the days to first mortality after a 7‐day Edwardsiella tarda challenge (P<0.05). In addition, under the experimental conditions, dietary vitamin E and n‐3 HUFA had a synergistic effect on the non‐specific immune responses and disease resistance in Japanese flounder (P<0.05).     

Acute toxicity of nitrite to mud crab Scylla serrata (Forsskål) larvae

Early larval stages of mud crab Scylla serrata were exposed to different concentrations of nitrite (40, 80 and 160 mg L⁻¹ and a control, without added nitrite) and three salinity levels (25, 30 and 35 g L⁻¹) using a static renewal method. No interactive effect of nitrite and salinity was detected. Estimated LT₅₀ in 96‐h toxicity tests decreased in all stages with increasing nitrite concentrations in all salinity levels. The 96‐h LC₅₀ values of nitrite‐N were 41.58, 63.04, 25.54, 29.98 and 69.93 mg L⁻¹ for zoea 1, 2, 3, 4 and 5 respectively. As the larvae grew, they showed a progressive increase in tolerance to nitrite. The toxicity of nitrite to larvae increased with exposure time. The median lethal concentration was not affected by salinity. The chloride component of salinity within 25–35 g L⁻¹ did not seem to be as effective in alleviating toxicity as has been reported in other crustacean species. Based on 96‐h LC₅₀ and an application factor of 0.1, the ‘safe level’ of rearing mud crab larvae was calculated to be 4.16, 6.30, 2.55, 2.99 and 6.99 mg L⁻¹ nitrite‐N for zoea 1, 2, 3, 4 and 5 respectively.     

Dietary protein concentration and daily feed allowance influence response of channel catfish, Ictalurus punctatus (Rafinesque), to ractopamine

Year-1 channel catfish, Ictalurus punctatus (Rafinesque) (average initial weight, 48 g) were fed diets containing 240 g kg^?1, 300 g kg^?1, or 360 g kg^?1 dietary protein with 0 or 20 mg kg^?1 ractopamine to satiation and diets containing 240 g kg^?1 and 360 g kg^?1 protein with 0 or 20 mg kg^?1 ractopamine at a restricted rate (60% of satiation) in aquaria at 29 ± 2°C for 8 weeks. Fish fed ractopamine at the 360 g kg^?1 protein level gained significantly more weight than controls when fed to satiation but not when the ration was restricted. Fish fed ractopamine at the 240 g kg^?1 protein level did not gain more weight than the controls at satiation or restricted feeding. Fish fed ractopamine in the diet containing 300 g kg^?1 protein gained significantly more weight than controls when fed to satiation. Ractopamine caused no significant differences in feed conversion at the 240 g kg^?1 or 360 g kg^?1 protein levels with restricted or satiation feeding. Muscle fat decreased when ractopamine was fed at all dietary protein levels and at both feeding rates. Muscle protein increased with ractopamine feeding in all treatments except the high-protein, satiation treatment. Weight gain response of year-1 channel catfish to ractopamine is dependent upon nutrient concentration of the diet and ration size; however, the effect of ractopamine on muscle composition of channel catfish is less dependent on nutrient concentration or amount of diet fed.     

Effects of various corn distillers by‐products on growth,feed efficiency,and body composition of channel catfish,Ictalurus punctatus

A study was conducted to examine the use of corn distillers’ by‐products in diets and the effects of additional dietary fat on channel catfish, Ictalurus punctatus, performance. Juvenile channel catfish (initial weight: 12.6 g per fish) were stocked in flow‐through aquaria and fed one of six practical diets for 9 weeks. Fish fed the control + fat diet consumed more diet and had higher feed efficiency ratio (FER) than fish fed the control diet, but weight gain was not significantly different between fish fed these two diets. Fish fed the diet containing 300 g kg^?1 distillers dried grains with solubles (DDGS) consumed more diet and gained more weight, but had similar FER compared with fish fed the control + fat diet. The diet containing 200 g kg^?1 high‐protein distillers grains (HPDDG) resulted in similar diet consumption, weight gain and FER as the control + fat diet. Fish fed the diet containing 100 g kg^?1 distillers solubles (DS) consumed more diet, but had similar weight gain and FER compared with fish fed the 300 g kg^?1 DDGS diet. The presence of distillers solubles in the diet (300 g kg^?1 DDGS, 100 g kg^?1 DS, 100 g kg^?1 EDS diets) appears to increase diet consumption, weight gain, and FER over the control diets with or without additional fat.     

Effects of dietary ascorbic acid supplementation on the growth performance,immune and stress response in juvenile Leiocassis longirostris Günther exposed to ammonia

This experiment was designed to investigate the effect of dietary supplemental ascorbic acid (AA) on the feed intake, growth, serum lysozyme, hepatic superoxide dismutase (SOD) and handling stress response in Chinese longsnout catfish (Leiocassis longirostris Günther) exposed to three levels of unionized ammonia nitrogen (UIA‐N). Juvenile Chinese longsnout catfish were reared in 54 fibreglass tanks with a 3 × 3 factorial design treatment consisting of three supplemental AA levels in ascorbyl 2‐monophosphate (38, 364 and 630 mg AA equivalent kg^?1 diet) and three UIA‐N concentrations [0.004 (the control), 0.037 and 0.292 mg L^?1]. The fish were sampled on the 11th, 32nd and 60th day. On the 62nd day, the remaining fish were subjected to an acute stress by being held in a dipnet out of water for 60 s, and sampled at 30 min post handling. The results showed that the specific growth rate (SGR) in 32 days significantly decreased with increased water UIA‐N (P=0.0476) but was not affected by dietary supplemental AA (P>0.05). After 60 days, SGR, feeding rate (FR) and feed conversion efficiency (FCE) significantly increased with increased dietary supplemental AA (P<0.001) while remaining unaffected by water UIA‐N (P>0.05). There was no significant interaction between dietary AA and UIA‐N for growth responses (P>0.05). The serum lysozyme activity on the 11th day and the hepatic SOD activity on the 32nd day were significantly affected at high (0.292 mg L^?1) water UIA‐N. On the 62nd day, the increase in cortisol resulting from acute stress significantly decreased by higher UIA‐N (P=0.038). It is suggested that Chinese longsnout catfish displayed an adaptive response after long‐term UIA‐N exposure, and AA had beneficial effects on the growth and feed intake of catfish and alleviated the negative effects of chronic ammonia stress. A chronically higher ammonia level shows a tendency to inhibit the cortisol response to another acute stressor.