Inducement of sex reversal in Sarotherodon niloticus (Linnaeus)

Two androgens, ethynyltestosterone (ET) and methyltestosterone (MT) and two estrogens, diethylstilbestrol (DES) and estrone (E) were orally administered to gonadally undifferentiated Sarotherodon niloticus fry. Diets with hormones were prepared at the following levels: ET and MT at 30 and 60 mg kg^?1 of feed, DES at 25 and 100 mg kg^?1 of feed, and E at 100 and 200 mg kg^?1 of feed. The fish were fed at 10% body weight per day for 25-, 35- and 59-day periods.All-male populations were produced with ET-60 and MT-60 in all three treatment periods, and with ET-30 and MT-30 during the 35- and 59-day treatments.No estrogen treatment resulted in 100% female populations but only about 10% of the DES-100 treatment populations at the three durations were males.Sex ratios were significantly different (P < 0.01) from the expected 1:1 ratio in all fish treated with androgens and estrogens. No ovotestis condition was found. Total mortalities in all treatments and controls were uniformly low, ranging from 1.5 to 8.8% for the treatment period.     

Hyperaccumulation of selenium in hybrid striped bass: a functional food for aquaculture?

One method of increasing the value of aquacultured product is to produce fillets that are fortified with minerals that are beneficial to human health – that is enhance the functionality of an already healthy product. A good candidate mineral in this regard is selenium (Se) which is of vital importance to normal metabolism in humans. In order to evaluate the dose response and tissue accumulation of supplemental dietary Se, a study was undertaken with hybrid striped bass (HSB). Animals were fed diets supplemented with either organic (0–3.2 mg kg^?1 as SelPlex^®) or inorganic (0.2 and 0.4 mg kg^?1 as sodium selenite) Se for 6 weeks. Because basal fishmeal‐based diets contained 1.22 mg Se kg^?1, doses of Se delivered equated to 1.22–4.42 mg kg^?1. At trial end, greatest weight gain was observed in fish receiving 0.2 mg Se kg^?1, irrespective of form (organic/inorganic). Se accumulation in HSB liver and fillet revealed a classical dose‐response once a threshold level of 0.2 mg Se kg^?1 was surpassed. Greatest tissue accumulation of Se was observed in fish fed the 3.2 mg Se kg^?1 level (P > 0.0001). A 100 g portion of Se‐enhanced HSB fillet would contain between 33 and 109 μg Se, amounting to a dietary intake of between 25 and 80 μg Se; a level that would satisfy present daily intake recommendations. Comparison of tissue Se levels indicated that the muscle provides a more conspicuous gauge of dietary Se dose‐response than does liver. Dietary treatments of between 0.4 and 1.6 mg organic Se kg^?1 reduced (P < 0.024) plasma glutathione peroxidase (GSH‐Px) activity. No differences were observed in ceruloplasmin, lysozyme or GSH‐Px activities between organic and inorganic Se when delivered at the 0.2 mg Se kg^?1 level. Ceruloplasmin, lysozyme and GSH‐Px levels were elevated (P ≥ 0.025) in fish fed the diet containing 0.4 mg inorganic Se kg^?1.     

Effect of dietary bovine lactoferrin on growth,haematology and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effect of dietary lactoferrin (Lf) on growth, haematology and non‐specific immune response of rainbow trout Oncorhynchus mykiss (Walbaum). Fish were fed an experimental diet containing 0 (as control), 50, 100, 200 and 400 mg Lf kg^?1 diet twice daily for 8 weeks and sampled at 2, 4, 6 (immune function and growth), and 8 weeks (immune function, haematology and growth). Statistical analyses revealed no significant effects of dietary Lf on growth performance (specific growth rate, weight gain, feed conversion ratio, feed intake and condition factor) or haematological parameters (red and white blood cell count, haemoglobin, haematocrit, serum iron and total iron binding capacity [TIBC]). Among the serum non‐specific immune parameters, lysozyme activity increased significantly in fish fed 100, 200, or 400 mg Lf kg^?1 feed for 8 weeks, whereas haemolytic complement activity increased in fish fed 100 and 400 mg Lf kg^?1 diet after 6 weeks. The antiprotease activity increased in groups fed 100, 200 or 400 mg Lf kg^?1 diet after 8 weeks. However, no significant effect was observed on serum peroxidase level. It can be concluded that feeding of rainbow trout on the diet supplemented with 100 mg kg^?1 or higher for 8 weeks enhances the non‐specific immune response.     

Partial replacement of fish meal with plant protein sources using organic acids to practical diets for juvenile yellowtail,Seriola quinqueradiata

An experiment was conducted to investigate the effects of phosphorus (P), citric acid (CA) and formic acid (FA) supplementation on growth and loading of nitrogen (N) and phosphorus (P) in juvenile yellowtail fed fish meal (FM) and alternate plant protein (APP) diets. Six diets designated as F49 (490 g kg^?1 FM‐based), F49 + P (490 g kg^?1 FM with 5 g kg^?1 inorganic P), F31 + CA (310 g kg^?1 FM containing 200 g kg^?1 APP with 5 g kg^?1 CA), F31 + FA (310 g kg^?1 FM having 200 g kg^?1 APP with 4 g kg^?1 FA), F23 + CA (230 g kg^?1 FM containing 300 g kg^?1 APP with 5 g kg^?1 CA) and F23 + FA (230 g kg^?1 FM having 300 g kg^?1 APP with 4 g kg^?1 FA) were formulated. Yellowtails were fed one of the diets for 12 weeks under on‐site conditions at water temperature 22.0–27.0 °C. F49 + P gave the best growth, while F23 + CA the lowest. Specific growth rate and feed conversion ratio of F31 + CA were similar with control group. Addition of CA to APP diets significantly increased retention of P; hence, its excretion was lowered. The results of this study suggest that FM could be replaced up to 70% with the addition of 5 g kg^?1 CA to a low P‐containing plant protein sources diet without inorganic P supplementation in juvenile yellowtail diets, which in turn would enable a reduction in environmental pollution from aquafeeds.     

The pigmenting effect of different carotenoids on fancy carp (Cyprinus carpio)

The optimal concentration of a panel of individual and combined carotenoid sources on skin pigmentation in fancy carp was investigated by nine experimental diets that were formulated and supplemented with astaxanthin at 25 mg kg^?1, lutein at 25 and 50 mg kg^?1, β‐carotene at 25, 50 and 75 mg kg^?1, and lutein combined with β‐carotene at 25 : 25 and 50 : 50 mg kg^?1, while a diet without supplemented carotenoid served as a control. The results showed that serum TC of fish fed diets containing supplemented with lutein plus β‐carotene at 25 : 25; 50 : 50 mg kg^?1 and lutein 50 mg kg^?1 diet were higher than the other treatments (P ≤ 0.05). Serum TC of the respective treatments was 6.2 ± 2.0, 7.8 ± 3.3 and 7.3 ± 1.9 μg mL^?1 serum, respectively. Fish fed diets combined with lutein and β‐carotene at 25 : 25, 50 : 50 mg kg^?1 and lutein 50 mg kg^?1 diet had serum astaxanthin concentrations similar to fish fed the diet with astaxanthin alone at 25 mg kg^?1. Serum astaxanthin concentrations was 0.7 ± 0.01, 0.9 ± 0.01, 0.4 ± 0.02 and 1.7 ± 0.18 μg mL^?1 serum, respectively. The chromaticity of fish body skin of red and white position was assessed by colourimetry using the CIE L*a*b (CIELAB) system. Pigmentation response of skin redness of fancy carp fed with diets combined with lutein and β‐carotene at 25 : 25, 50 : 50 mg kg^?1 and lutein 50 mg kg^?1 were higher than other treatments (P ≤ 0.05) but they were similar to fish fed with 25 mg kg^?1 astaxanthin diet. The redness (a* values) of fish fed diets with diets combined with lutein and β‐carotene at 25 : 25, 50 : 50 mg kg^?1 and lutein 50 mg kg^?1 were 28.3 ± 0.53, 29.9 ± 1.38, 28.8 ± 3.95 and 28.5 ± 2.49, respectively. After 3 weeks of feeding the experimental diets, the fish fed on a diet without carotenoid supplement for one week demonstrated that the same three groups still retained their redness and had an overall tendency to improve skin colouring. Finally, concentrations 50 mg kg^?1 of lutein, or the combination of lutein and β‐carotene at 25 : 25 mg kg^?1 showed the highest efficiency for improving skin pigmentation and redness of skin.     

Effects of dietary squid viscera meal on growth and cadmium accumulation in tissues of Japanese seabass, Lateolabrax japonicus (Cuvier 1828)

Cadmium (Cd) is a toxic environmental pollutant with a long biological half‐life and can produce both hepatic and renal injuries in mammals and fish. Squid viscera meal (SVM), an effective attractant for aquatic animals, is widely used as an ingredient in aquafeeds. However, SVM is rich in Cd and its complexes. A study was conducted to evaluate the effects of dietary SVM on the growth and Cd deposition in tissues of Japanese seabass, Lateolabrax japonicus. Three practical diets were formulated to contain 0, 50 and 100 g SVM kg^?1 diet, respectively, containing 0.21, 7.26 and 12.08 mg Cd kg^?1 diet. Each diet was randomly assigned to triplicate groups of 80 Japanese seabass (mean initial weight, 10.89±0.21 g) in floating sea cages (1.5 × 1.5 × 2.0 m). Fish were fed twice daily (06:30 and 16:30 hours) to satiation for 8 weeks. The results showed that there were no significant differences in fish survival among three dietary treatments, but significant higher specific growth rates (SGR) were observed in the fish fed diets with 50 or 100 g SVM kg^?1 diet than that from the control group (P<0.05). The Cd concentrations in the kidney, liver and gill were found in a decreasing order at each treatment, and positively correlated with dietary Cd levels. Fish fed diets with 50 and 100 g SVM kg^?1 diet had significantly higher Cd accumulations in the kidney (3.25, 5.85 mg kg^?1), liver (0.76, 1.26 mg kg^?1) and gill (0.42, 0.58 mg kg^?1) compared with the control group (0.82, 0.34 and 0.32 mg kg^?1 respectively) (P<0.05). The Cd concentration in fish muscle; however, was undetectable in any treatment. Therefore, based on these results, accumulation of Cd in edible tissue (muscle) of farmed Japanese seabass is not a food safety issue. However, long‐term feeding of diets with SVM may result in accumulation of Cd in the kidneys, liver and gills of fish.     

Effect of vitamin C and astaxanthin on stress and disease resistance of postlarval tiger shrimp, Penaeus monodon (Fabricius)

Postlarvae of tiger shrimp, Penaeus monodon (Fabricius), were fed semipurified diets supplemented with various levels of astaxanthin (AX) and ascorbic acid-polyphosphate (ApP): three groups were fed 230 mg AX kg^?1 diet combined with 100, 1700 and 3400 mg ascorbic acid (AA) kg^?1 diet, respectively; two diets contained 810 mg AX kg^?1 mixed with 200 and 1700 mg AA kg^?1, respectively. Each treatment was run in four replicates. Incorporated levels of AA and AX, production output, and physiological condition were recorded after 4 weeks of feeding. Whole-body AA (21-47 μg g^?1) and AX, concentrations (19-35 μgg^?1) were linked to dietary ApP and AX supply, respectively, although not significantly for the latter. The biomass of the group receiving the lower dietary ApP-AX combination was significantly lower than for all other treatments, i.e. 3.1 versus 3.9 g, respectively. In the groups fed 230 mg AX kg^?1 diet, significant differences in stress resistance were observed according to the dietary ApP level, i.e. raising the vitamin C content in the feed from 100 to 3400 mg AA kg^?1 resulted in a concomitant drop in mortality after an osmotic shock. For the treatments receiving 810 mg AX kg^?1 diet, the beneficial effect of extra dietary vitamin C was not significant. An increase in the dietary AX for shrimp fed comparable ApP levels resulted in a significant drop of the stress index from 56 to 33 (cumulative mortality index). An increased resistance to salinity shock was demonstrated in association with supplementation of high dietary AA or AX levels. No conclusive results regarding possible improved disease resistance could be made since no mortality was observed after a disease challenge with Vibrio harveyi.     

The influence of phytoestrogens and oestradiol-17β on growth and sex determination in the European eel (Anguilla anguilla)

Under aquaculture conditions, European eels (Anguilla anguilla) produce a high percentage of males (80–95%) that normally stop growing at 100–200 g. Females continue to grow to 500–750 g and obtain higher market value. Therefore, increasing the percentage of females in a population would be beneficial to the culture of eels. The present study was carried out in order to examine the effect of oestradiol and phytooestrogens on sex differentiation and growth rate of eels. Juvenile European eels with undifferentiated gonads were fed pellets containing oestradiol‐17β (E2) or phytooestrogens for 100–150 days. Feeding E2 resulted in 50–61% increase in body weight compared with the control. Oestradiol‐17β and phytooestrogens both elevated significantly the percentage of females in the population. Feeding E2 at 20 mg kg^?1 feed resulted in 70% females, while lower concentration of E2 (2 mg kg^?1) resulted in only 30% after 100 days (Experiment 1). The same dose given for 150 days (Experiment 2) resulted in 88% females, indicating that both, the concentration and duration of E2 treatments had a significant effect on sex differentiation. Fish fed genistein at 2 mg kg^?1 for 100 days, resulted in 55% of females, but at a higher dose of 20 mg kg^?1 there were only 15% females. These results demonstrate that phytooestrogens can be used as alternatives to gonadal steroids for sex manipulation in eels, but the optimal concentrations and duration are still to be determined.     

Antioxidant effect of dietary tocopherol and ascorbic acid on growth and survival of Litopenaeus vannamei postlarvae

The nutritional effect of vitamin E in dietsfor Litopenaeus vannamei postlarve (PL19)was investigated. Four formulated diets withdifferent combinations of α-tocopherylacetate (α-TA), ascorbic acid (AA) andhighly unsaturated fatty acids (HUFA) weretested, using four replicates. No significant differences in survival wereobserved among treatments after 34 days offeeding. However, shrimp fed with a dietcontaining 2% fish oil (low n-3 HUFA content),200 mg.kg^?1 α-TA and100 mg.kg^?1 AA (diet H/E/C) showedsignificantly better growth than those fed adiet supplemented with 5% fish oil (high n-3HUFA content), 200 mg.kg^?1 α-TA and100 mg.kg^?1 AA (diet H+/E/C). Shrimp fedwith a diet containing 5% fish oil,900 mg.kg^?1 α-TA and100 mg.kg^?1 AA (diet H+/E+/C) showed a significantly higher tissue level of n-6 PUFAthan postlarvae fed diet H+/E/C. No definiteconclusion could be drawn about a possibleinteraction between α-TA and AA, since acomparison of the diet containing 5% fish oil,200 mg.kg^?1 α-TA and700 mg.kg^?1 AA (H+/E+/C+) and the dietH+/E/C did not show any significant differencesin any of the measured parameters. Theantioxidative status of the shrimp tissue(measured by means of the thiobarbituric acid(TBA) assay and expressed as nM malonaldehyde(MA) per gramme dry weight) was equal for alltreatments. Nevertheless, there was a slightlylower MA value with the diet H+/E/C+,indicating that AA may be an effectiveantioxidant in the aqueous phase and at thewater/lipid interface of the tissue. The tissuelevels of α-T and AA were highlydependent on the amounts in diets and nocorrelation between α-T and AAincorporation could be observed.     

Effect of dietary protein and lipid levels and protein–energy ratio on growth indices, feed utilization and body composition of freshwater prawn, Macrobrachium rosenbergii (de Man 1879) post larvae

A grow‐out experiment was designed to determine the effect of different dietary protein, lipid levels and protein–energy (P:E) ratio on growth performance and feed utilization of the freshwater prawn, Macrobrachium rosenbergii post larvae (PL) culture in pond net enclosures (hapa, 3.75 m^?3 each) for 12 weeks (84 days). The experimental treatments were assigned in triplicate. Six test diets were formulated to contain three different protein levels (300, 350 and 400 g kg^?1 diet) and two lipid levels (100 and 140 g kg^?1 diet) in a factorial manner (3 × 2) to provided six different dietary P:E ratio: 16, 17, 18, 19, 20 and 21 mg CP kJ^?1 g^?1). The result showed that the highest significant (P≤0.05) survival rate, growth indices and feed utilization were observed for M. rosenbergii PL fed a diet with a P:E ratio of 17 mg CP kJ^?1 g¹, whereas, the lowest value was recorded for prawns fed a diet with a P:E ratio of 20 mg CP kJ^?1 g^?1. Whole body contents of protein and lipid were highest (P≤0.05) when fed diets with 21 and 17 mg CP kJ^?1 g^?1 respectively. Concerning dietary protein levels, the highest (P≤0.05) values for survival and growth indices were observed for PL fed a diet containing 300 g kg^?1 diet protein. The same trend was observed for PL fed a diet with 100 g kg^?1 diet lipid level, irrespective of dietary protein levels. A diet containing 300 g kg^?1 protein and 100 g kg^?1 lipid with a dietary P:E ratio of 17 mg CP kJ g^?1 is recommended to stimulate growth performance and nutrients utilization efficiency of M. rosenbergii PL.     

Fluoride retention of Atlantic salmon (Salmo salar) fed krill meal

The present experiment was performed to study how fluoride from krill meal enriched muscle, whole fish and bone of adult Atlantic salmon (Salmo salar) reared in sea water. Atlantic salmon (mean weight 0.5 kg) were divided into four triplicate groups and fed a commercial fish meal based diets with 0, 100, 200 and 300 g krill kg^?1 feed, respectively, for 12 weeks. The fluoride concentrations in the experimental feeds were analysed to be 18, 132, 235 and 358 mg kg^?1, respectively. Growth, mortality and feed efficiency were recorded through the experiment. Fluoride concentration was measured in muscle, whole‐body, and bone initially and after 12 weeks of feeding. The fluoride concentrations in the samples were determined by alkali fusion and fluoride ion‐selective electrode. Growth, mortality and feed efficiency ratio were not affected by the dietary treatments. The results showed that fluoride concentration in muscle, whole body and bone were not affected by the dietary fluoride level. The fluoride concentration in the tissues showed great variation among replicates of the group given the same diet. Fillets of the fish varied between 0.3 and 1.4 mg fluoride kg^?1 wet weight, whereas the whole‐body concentration of fluoride varied between 3.3 and 6.1 mg kg^?1 wet weight and the fluoride bone concentration varied between 5.8 and 7.2 mg kg^?1 fresh weight. These results suggest that Atlantic salmon are highly tolerant of dietary fluoride given as krill meal with concentration of fluoride up to 350 mg kg^?1 diet, and that accumulation of fluoride from feeding diets containing krill meal does not lead to tissue accumulation in the fish, at least over a short period of time.     

Dietary administration of soybean isoflavones enhances the immunity of white shrimp Litopenaeus vannamei and its resistance against Vibrio alginolyticus

The growth response, total hemocyte count (THC), respiratory burst (release of superoxide anion), phenoloxidase (PO) activity, superoxide dismutase (SOD) activity, nitric oxide synthase (NOS) activity and resistance to the pathogen Vibrio alginolyticus were measured in white shrimp (Litopenaeus vannamei) which had been fed diets supplemented with soybean isoflavones (SI) at 0, 5, 10, 20, 40 mg kg^?1 feed for 8 weeks. Dietary SI had no significant influence on survival rate of the shrimp. Significantly greater SGR was observed in treatments with 10, 20 and 40 mg kg^?1 SI supplement than that in control (P < 0.05). Shrimp fed a diet with 20 mg kg^?1 SI showed significant increase in THC, PO activity, respiratory burst activity, SOD activity as well as NOS activity (P < 0.05). Increased THC, respiratory burst activity, SOD activity and NOS activity were also noticed in shrimp fed SI at 10 or 40 mg kg^?1 (P < 0.05). Significant lower cumulative mortality after challenge was observed in shrimp fed diets with SI supplement (10.0–13.3%) than that in control group (36.7%) (P < 0.05). It is therefore concluded that oral administration of SI at 20 mg kg^?1 for 8 weeks could enhance the immune ability of shrimp and improve production in shrimp farming.     

Bioavailability and interactions with other micronutrients of three dietary iron sources in Atlantic salmon, Salmo salar, smolts

Atlantic salmon, Salmo salar L., with mean initial weight of 60 g were fed a diet based on cod muscle meal supplemented with elemental iron, iron sulphate or haem-bound iron in concentrations of 0, 25, 50, 100, 500 and 1500 mg iron kg^?1 for 8 weeks. No significant differences in growth or mortality were found, except in fish fed 1500 mg haem iron kg^?1, which showed reduced growth. In fish fed diets supplemented with elemental iron below 1500 mg iron kg^?1, blood haemoglobin and hepatic iron concentration decreased compared with fish fed the unsupplemented diet. Fish fed diets supplemented with iron sulphate showed increased blood haemoglobin and hepatic iron concentrations between 25 and 100 mg iron kg^?1. Fish fed diets supplemented with haem-bound iron showed increased hepatic iron at all dietary iron levels, while blood haemoglobin concentration decreased in the group fed 1500 mg haem iron kg^?1. The bioavailability of haem iron relative to sulphate iron was calculated by the slope ratio method to be 239% and 148% using blood haemoglobin and hepatic iron, respectively. Relative bioavailability of elemental iron was zero when dietary supplementation levels were between 25 and 500 mg iron kg^?1, while a small part was utilized when 1500 mg elemental iron kg^?1 was supplemented. Additions of 500 and 1500 mg haem-bound iron kg^?1 resulted in a complete loss of ascorbic acid in these diets. When these groups were discounted, no significant relationship between hepatic iron and hepatic ascorbic acid was found. There was no significant effect of dietary iron on whole-body manganese concentration and only a weak effect on whole-body zinc concentration. No significant correlations between dietary iron and hepatic copper concentration were found in any of the dietary treatments. This study also showed that the level of inorganic iron supplementation may be reduced by inclusion of 20 g blood meal kg^?1 in the diet.     

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.     

Non-gelatinized corn supplemented with α-amylase at sub-optimum protein level enhances the growth of Labeo rohita (Hamilton) fingerlings

A feeding trial was conducted for 60 days to delineate the effect of both gelatinized and non‐gelatinized corn with or without supplementation of exogenous α‐amylase at two level of protein 35% (optimum) and 27% (sub‐optimum) on growth, tissue composition and protein sparing effect of carbohydrate in the diet of Labeo rohita fingerlings. Three hundred and sixty fingerlings (average weight 10.00±0.15 g) were randomly distributed in 12 treatment groups with two replicates for each. Twelve semi‐purified diets containing either 35% or 27% CP were prepared with different levels of α‐amylase (0, 50, 100 and 150 mg kg^?1) and starch type [gelatinized (G)/non‐gelatinized, (NG)] viz. T₁ (NG, 35% CP, 0 mg kg^?1α‐amylase), T₂ (G, 35% CP, 0 mg kg^?1α‐amylase), T3 (NG, 27% CP, 50 mg kg^?1α‐amylase), T₄ (NG, 35% CP, 50 mg kg^?1α‐amylase), T₅ (G, 27% CP, 50 mg kg^?1α‐amylase), T₆ (G, 35% CP, 50 mg kg^?1α‐amylase), T₇ (NG, 27% CP, 100 mg kg^?1α‐amylase), T₈ (NG, 35% CP, 100 mg kg^?1α‐amylase), T₉ (G, 27% CP, 100 mg kg^?1α‐amylase), T₁₀ (G, 35% CP, 100 mg kg^?1α‐amylase), T₁₁ (NG, 27% CP, 150 mg kg^?1α‐amylase) and T₁₂ (NG, 35% CP, 150 mg kg^?1α‐amylase). The fish were acclimatized to the experimental condition for 24 days during which control diet (NG, 35% CP) was fed. Weight gain percentage, specific growth rate, protein efficiency ratio and apparent net protein utilization of NG corn‐fed groups at 42.43% were significantly higher (P<0.05) than the same level of G corn‐fed groups. We conclude that 42.43% NG corn supplemented with 50 mg α‐amylase kg^?1 feed at sub‐optimum level of CP (27%) significantly enhanced the growth and protein in L. rohita fingerling. Addition of dietary α‐amylase to G corn had no added advantage on growth of L. rohita fingerling.     

Effect of oestradiol-17β immersion treatments on sex reversal of mud loach, Misgurnus mizolepis (Günther)

Mud loach, Misgurnus mizolepis (Günther), were sex reversed using the immersion technique. Fry were raised in water containing 50, 100 or 200 μg oestradiol-17β I^?1 for 1, 2 or 3 weeks. Survival rates decreased as dose and duration of treatment increased: in most instances they were significantly (P < 0.05) lower than those of the controls. Growth rates were unaffected except for fish in the 200 μg I^?1 treatments. The 200 μg T^?1 treatments for 2 and 3 weeks produced monosex female populations. The 100 μg I^?1 treatment for 3 weeks produced 99% females and 1% intersex individuals. Histologically, ovaries of sex-reversed fish were similar to those of normal females. Morphologically, however, they were different in that the ovaries of sex-reversed fish were not connected to the genital pore. The hormone treatments affected the size and morphology of the pectoral fins, which exhibit sexual dimorphism in mud loach.     

Susceptibility of channel catfish (Ictalurus punctatus) fed with dietary sodium chloride to nitrite toxicity

Juvenile channel catfish (Ictalurus punctatus) were fed with nutritionally complete, basal diets supplemented with NaCl at 0, 10, 20 or 40 g kg^?1 diet (0, 1, 2, or 4%) to apparent satiation twice daily for 10 weeks. Catfish were exposed to nitrite after six (7.70 mg L^?1 nitrite‐N) and ten (7.18 mg L^?1 nitrite‐N) 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 haematology (haematocrit, haemoglobin and methaemoglobin) and plasma electrolyte dynamics (nitrite, chloride, sodium and potassium). Mortality from nitrite toxicity was also determined. Mortality from nitrite exposure tended to decrease with increasing NaCl in the diet at 6 weeks and was significantly lower in the 40 g kg^?1 NaCl group (12.5%) compared to the control group (57.5%). A similar trend in mortality occurred at 10 weeks as well; however, the differences among dietary treatments were not significant. The improvements in blood MetHb (non‐significant), chloride and nitrite levels in catfish may at least in part be responsible for the improved survival after nitrite exposure, which trended in support of the prevailing hypotheses for the positive effects of NaCl on nitrite toxicity.     

Spawning induction in Kutum Rutilus frisii kutum (Kamenskii, 1901) using carp pituitary extract or GnRH analogue combined with metoclopramide

Kutum Rutilus frisii kutum (Kamenskii, 1901), Cyprinidae is an endemic fish of the Caspian Sea. Iranian Fisheries Organization (Shilat) produce up to 200 million fry (1–2 g body weight (b.w.)) to restock the Caspian Sea population annually. Some of these fry are produced by spawning induction in broodfish by carp pituitary extract (CPE). The objective of this study was to assay the effectiveness of the gonadotropin releasing hormone analogue (d ‐Ala⁶, Pro⁹‐Net GnRH) alone or in combination with metoclopramide (MET), a dopamine antagonist, on the percentage of ovulated females, latency period, ovulation index and fertilization success. The following hormone treatments were tested: single injection of 2 mg kg^?1 b.w. of CPE as a positive control, GnRHa alone 20 and 40 μg kg^?1 b.w. and combination of GnRHa and MET as follows: 5 μg+2.5 mg, 10 μg+ 5 mg and 20 μg+10 mg kg^?1 b.w. Negative control group was injected with 0.7% saline. The percentage of ovulated females, ovulation index and fertilization success were 90%, 71.3±1.24%, 68.4±2.3%, respectively, in the group treated with GnRHa+MET at a dose of 20 μg+10 mg kg^?1 b.w. and were significantly higher than those in the positive control (60%, 64.5±0.23%, 69.1±4.5%) (P<0.05). However, the latency period in this group was longer than that in the positive control (P<0.05). Only 20% and 40% fish ovulated in groups that received 20 or 40 μg kg^?1 b.w. GnRHa. No fish ovulated in the negative control.     

Effects of dietary protein to energy ratios on growth and body composition of juvenile Chinese sucker,Myxocyprinus asiaticus

A growth experiment was conducted to investigate effect of dietary protein to energy ratios on growth and body composition of juvenile Myxocyprinus asiaticus (initial mean weight: 10.04 ± 0.53 g, mean ± SD). Nine practical diets were formulated to contain three protein levels (340, 390 and 440 g kg^?1), each with three lipid levels (60, 100 and 140 g kg^?1), in order to produce a range of P/E ratios (from 22.4 to 32.8 mg protein kJ^?1). Each diet was randomly assigned to triplicate groups of 20 fish in 400‐L indoors flow‐through circular fibre glass tanks provided with sand‐filtered aerated freshwater. The results showed that the growth was significantly affected by dietary P/E ratio (P < 0.05). Fish fed the diets with 440 g kg^?1 protein (100 and 140 g kg^?1 lipid, P/E ratio of 31.43 and 29.22 mg protein kJ^?1) had the highest specific growth rates (SGR) (2.16 and 2.27% day^?1, respectively). However, fish fed the diet with 390 g kg^?1 protein and 140 g kg^?1 lipid showed comparable growth (2.01% day^?1), and had higher protein efficiency ratio (PER), protein productive value (PPV) and energy retention (ER) than other groups (P < 0.05). No significant differences in survival were found among dietary treatments. Carcass lipid content was positively correlated with dietary lipid level, but irrespective of protein level and inversely correlated with carcass moisture content. Carcass protein contents increased with increasing dietary lipid at each protein level. The white muscle and liver composition showed that lipid increased with increasing dietary lipid level (P < 0.05). Dietary protein concentrations had significant effect on condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) (P < 0.05). However, dietary lipid concentrations had no significant effect on CF, HSI (P > 0.05). Based on these observations, 440 g kg^?1 protein with lipid from 100 to 140 g kg^?1 (P/E ratio of 29.22 to 31.43 mg protein kJ^?1) seemed to meet minimum requirement for optimal growth and feed utilization, and lipid could cause protein‐sparing effect in diets for juvenile Chinese sucker.     

Effect of lipid supplementation on reproductive performance of female channel catfish,Ictalurus punctatus,induced and strip‐spawned for hybridization

The influence of different lipid sources and n3:n6 ratios on reproductive performance of female channel catfish, Ictalurus punctatus was evaluated. A commercial catfish feed was top coated with 2% oil and offered to brood stock females fish during 70–85 days before spawning season. Four dietary treatments were formulated using the following top coating ratios: diet 1, soybean oil 9.5 g kg^?1 and linseed oil 10.5 g kg^?1; diet 2, soybean oil 17.5 g kg^?1 and linseed oil 2.5 g kg^?1; diet 3, 20.0 g kg^?1 linseed oil, and diet 4, 10.0 g kg^?1 menhaden fish oil, supplemented with 5.0 g kg^?1 arachidonic acid (ARA), and 5.0 g kg^?1 docosahexaenoic acid (DHA). Fatty acid composition of the eggs reflected the effect of dietary treatment offered during spring season. Supplementation of ARA, EPA and DHA in commercial catfish feed in the form of menhaden fish oil with purified liquid algae extracts of ARA and DHA produced from two to five times the number of fry per female body weight when compared to the effect of fed top coated with vegetable oils. Although, this effect was not statistically significant it may represent an economical improvement for the industry.