Microbial Phytase Can Replace Inorganic Phosphorus Supplements in Channel Catfish Ictalurus punctatus Diets1

Abstract.– Juvenile channel catfish Ictalurus punctatus (initial weight: 6.8 g/fish) were fed four practical diets containing 0, 250, 500, and 750 units of microbial phytase/kg and a diet containing 1% feed grade dicalcium phosphate (but no microbial phytase) under laboratory conditions for 12 wk. Fish fed the diets containing 250 units of microbial phytase/kg and above consumed more feed, gained more weight, and had a lower feed conversion ratio (FCR) in comparison to fish fed the basal diet containing no microbial phytase. Fish fed the diet containing dicalcium phosphate had intermediate weight gain and feed conversion ratio as compared to fish fed the basal diet and diets containing microbial phytase. Bone ash and phosphorus concentrations were lower for fish fed the basal diet than for fish fed other diets. No differences in weight gain, feed consumption, FCR, bone ash and bone phosphorus were observed among fish fed the diets containing various levels of microbial phytase. Fish fed the diet containing dicalcium phosphate had a lower bone phosphorus concentration than fish fed diets containing microbial phytase. Fecal phosphorus concentrations were lower for fish fed the diets containing microbial phytase than for fish fed the basal diet and the diet containing dicalcium phosphate. Results from the present study indicated that addition of 250 units of microbial phytase/kg to practical diets can effectively improve bioavailability of phytate phosphorus to channel catfish and may possibly eliminate the use of an inorganic phosphorus supplement in channel catfish diets. However, these data must be verified in trials conducted in ponds, prior to recommending removal of supplemental phosphorus from channel catfish diets.     

Comparative Net Absorption of Chelated and Inorganic Trace Minerals in Channel Catfish Ictalurus punctatus Diets

Coefficients of net absorption for copper, iron, manganese, selenium, and zinc were determined for chelated sources (copper proteinate, iron proteinate, manganese proteinate, selenium proteinate, zinc proteinate) and inorganic sources (copper sulfate pentahydrate, ferrous sulfate heptahydrate, manganese sulfate monohydrate, sodium selenite, zinc sulfate hep-tahydrate) of these elements with channel catfish Ictalurus punctatus . Fish weighing approximately 60 g were placed into 40-L aquaria (12 fish/aquarium) at a temperature of 28 f 2 C and fed either an egg white-based, purified diet or a soybean meal-based, practical diet with and without the test mineral sources for 6 wk then killed and feces collected from the hindgut. Treatments were arranged in a 2 × 2 factorial design. Absorption coefficients for the elements in the basal and mineral supplemented diets were calculated by the indirect indicator (chromic oxide) method and corrected for residual amounts of element in the basal diets. Net absorption of the chelated minerals was significantly higher ( p < 0.05) than net absorption of the inorganic minerals in both basal diets. Average percentage improvement in net absorption of chelated minerals over inorganic minerals was 39.3% in the purified diets and 81.1% in the practical diets. These results may indicate that appreciably lower amounts of chelated trace minerals than inorganic trace minerals can be used as supplements in catfish feeds.     

Effects of Various Dietary Carotenoid Pigments on Fillet Appearance and Pigment Absorption in Channel Catfish, Ictalurus punctatus

A study was conducted to evaluate effects of various carotenoids on skin and fillet coloration and fillet carotenoid concentration in channel catfish, Ictalurus punctatus. For 12 wk, juvenile catfish were fed one of six experimental diets containing no supplemental carotenoid or 100 mg/kg of one of following carotenoid additions: β‐carotene (BCA), lutein (LUT), zeaxanthin (ZEA), canthaxanthin (CAN), and astaxanthin (AST). Visual yellow color intensity score was highest for fish fed LUT, followed by ZEA, AST, and CAN, and lowest for fish fed basal and BCA diets. Skin and tissue Commission Internationale de I’Eclairage yellowness value was the highest in fish fed LUT, followed by fish fed ZEA, AST, and CAN, and lowest for fish fed basal and BCA diets. Fish accumulated the supplemental carotenoids in muscle tissues, but concentrations of different carotenoids in the tissue varied greatly. Approximately 30% of the LUT added was converted to echineone; no conversion was observed among other supplemental carotenoids. Results from the present study indicate that channel catfish can accumulate yellow pigments LUT and ZEA and red or pink pigments CAN and AST in the flesh, resulting in yellow coloration. The yellow pigment BCA does not appear to deposit in skin or flesh at levels sufficient to alter the coloration.     

Iron Methionine and Iron Sulfate as Sources of Dietary Iron for Channel Catfish Ictalurus punctatus

The dietary iron requirement for normal growth and optimum hematological values and bioavailability was determined for channel catfish Ictalurus punctatus fingerlings using egg-white based diets supplemented with 0,5,10,20,60, and 180-mg iron/kg from iron methionine or 20, 60, and 180-mg iron/kg from iron sulfate. The basal diet which contained 9.2-mg iron/kg, 34% crude protein and 3.1 kcal of digestible energy/g was fed to channel catfish fingerlings (8.5 g) in triplicate flow-through aquariums to satiation twice daily for 8 wk. Fish fed the basal diet without iron supplementation exhibited poor growth throughout the 8-wk period. Fish fed iron-supplemented diets did not differ with regard to final weight gain. Survival, feed conversion, total blood cell count, mean corpuscular hemoglobin concentration, serum iron, total iron binding capacity, and transferrin saturation were not significantly affected by dietary iron level. Hemoglobin, hematocrit, mean corpuscular hemoglobin, and mean corpuscular volume were significantly lower in fish fed the basal diet. These values were also consistently lower for fish fed diets with 5 and 10-mg iron/kg from iron methionine. However, differences were not always significant. Results of this study indicate that supplementation of 5-mg iron from iron methionine was sufficient for growth. However, a supplemental iron level of 20-mg/kg diet or a total iron level of 30-mg/kg of diet appeared to be needed for optimum hematological values. Iron methionine and iron sulfate were equally effective in preventing anemia in channel catfish.     

Use of Microbial Phytase in Channel Catfish Ictalurus punctatus Diets to Improve Utilization of Phytate Phosphorus1

A 10-wk feeding trial was conducted in the laboratory during which channel catfish Ictalurus punctatus (average initial weight: 6.5 g/fish) were fed five practical diets containing either 0, 500, 1,000, 2,000, or 4,000 units of microbial phytase/kg diet. Fish fed diets containing 500 or more units of microbial phytase/kg consumed more feed and gained more weight than fish fed the basal diet without supplemental phytase. Feed conversion ratios (FCR) did not differ among treatments except the FCR for fish fed 1,000 units of microbial phytase/kg diet was lower than that of fish fed no supplemental phytase. Fish survival was not different among treatments. Contrast analysis showed that weight gain, feed consumption, bone ash, and bone phosphorus were higher and feed conversion ratio was lower for fish fed diets supplemented with phytase as compared to fish fed no supplemental phytase. The concentration of fecal phosphorus decreased linearly as phytase supplementation increased. Results from this study demonstrate that microbial phytase is effective in improving bioavailability of phytate phosphorus to channel catfish, which may eventually lead to a reduction in the amount of supplemental phosphorus added to commercial channel catfish feeds.     

Dietary Folic Acid and Bacterial Infections in Channel Catfish,Ictalurus punctatus

Channel catfish, Ictalurus punctatus, in a quadruplicate flowthrough aquaria for 15 weeks, were fed a semipurified basal diet containing no folic acid or with folic acid levels ranging from 0.2 to 10.0 mg/kg with or without antibiotic. A second study was conducted for 25 weeks under similar conditions but with semipurified diets containing either 20 or 200 mg/kg ascorbic acid and either 0, 0.4, or 4.O.mg/kg folic acid in a factorial design. Mortalities throughout both experiments were monitored and the etiological causes noted. Fish remaining from the second study were overwintered in circular tanks, kept on the same experimental diets, and challenged with Edwardsiella ictaluri after having been on experimental diets for 50 weeks. In both studies, the addition of folk acid to the basal experimental diet resulted in a decreased incidence of columnaris, Flexibacter columnaris. Folic acid concentration in the diet significantly affected mortalities in fish exmrimentallv challenged with E. ictaluri; however, there was significant interaction between the folic acid concentration and the concentration of ascorbic acid. At the lower concentration of ascorbic acid, 4 mg/kg of folic acid was required to reduce mortalities, but at the higher concentration of ascorbic acid, only 0.4 mg/kg folic acid was needed to reduce mortalities below that of the diet without folk acid. Antibody tilers were not affected by folic acid concentration at the lower concentration of ascorbic acid; however at the higher concentration of ascorbic acid, the diets containing 0.4 or 4 mg/kg of folic acid resulted in increased antibody production.     

Effect of Dietary Protein Concentration on Growth and Processing Yield of Channel Catfish Ictalurus punctatus1

Abstract.— This study was conducted to evaluate the effect of dietary protein concentration and an all‐plant diet on growth and processing yield of pond‐raised channel catfish Ictalurus punctatus. Four diets were formulated using plant and animal proteins to contain 24%n, 28%, 32%, or 36% crude protein with digestible energy to protein (DE/P) ratios of 11.7, 10.2, 9.0, and 8.1 kcal/g, respectively. An all‐plant diet containing 28% protein with a DE/P ratio of 10.2 kcal/g was also included. Channel catfish fingerlings averaging 40 g/fish were stocked into 24, 0.04‐ha ponds at a density of 18,530 fish/ha. Five ponds were used for each dietary treatment except for the all‐plant diet which had four replicates. The fish were fed once daily to apparent satiation for 160 d. No differences were observed in feed consumption, weight gain, survival, carcass and nugget yield, or fillet moisture and protein concentrations among treatments. Fish fed the 28% protein diet had a lower feed conversion ratio (FCR) than fish fed diets containing 24% and 32% protein, but had a FCR similar to fish fed the 36% protein diet. Fillet yield was higher for fish fed the 36% protein diet than fish fed the 24% protein diet. Visceral fat was lower in fish fed the 36% protein diet than fish fed other diets. Fish fed the 32% and 36% protein diets exhibited a lower level of fillet fat than fish fed the 24% protein diet. The 36% protein diet resulted in a lower level of fillet fat than fish fed the 28% protein diet. There was a positive linear regression in fillet yield and fillet moisture concentration and a negative linear regression in visceral fat and fillet fat against dietary protein concentration. No differences in any variables were noted between the 28% protein diets with and without animal protein except that fish fed the 28% protein diet without animal protein had a higher FCR than fish fed the 28% protein diet with animal protein. This observation did not appear to be diet related since FCR of fish fed the 32% protein diet containing animal protein was not different from that of fish fed the 28% all‐plant protein diet. Data from the present study indicate that dietary protein concentrations ranging from 24% to 36% provided for similar feed consumption, growth, feed efficiency, and carcass yield. However, since there is a general increase in fattiness and a decrease in fillet yield as the dietary protein concentration decreases or DEP ratio increases, it is suggested that a minimum of 28% dietary protein with a maximum DEIP ratio of 10 kcal/g protein is optimal for channel catfish growout.     

Effect of Dietary Protein Concentration and Stocking Density on Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctatus

Diets containing 28% and 32% crude protein were compared for pond‐raised channel catfish Ictalurus punctatus stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48.5 g/fish were stocked into 30 0.04‐ha ponds. Five ponds were randomly allotted for each dietary protein ± stocking density combination. Fish were fed once daily to satiation for two growing seasons. There were no interactions between dietary protein concentration and stocking density for any variables. Dietary protein concentrations (28% or 32%) did not affect net production, feed consumption and weight gain per fish, feed conversion ratio, survival, processing yields, fillet moisture, protein and ash concentrations, or pond water ammonia and nitrite concentrations. Fish fed the 32% protein diet had slightly but significantly lower levels of visceral and fillet fat than fish fed the 28% protein diet. As stocking density increased, net production increased, while weight gain of individual fish, feed efficiency, and survival decreased. Stocking densities did not affect processing yield and fillet composition of the fish. Although highly variable among different ponds and weekly measurements, ponds stocked at the highest density exhibited higher average levels of total ammonia‐nitrogen (TAN) and nitrite‐nitrogen (NO₂‐N) than ponds stocked at lower densities. However, stocking density had no significant effect on un‐ionized ammonia‐nitrogen (NH₃‐N) concentrations, calculated based on water temperature, pH, and TAN. By comparing to the reported critical concentration, a threshold below which is considered not harmful to the fish, these potentially toxic nitrogenous compounds in the pond water were generally in the range acceptable for channel catfish. It appears that a 28% protein diet can provide equivalent net production, feed efficiency, and processing yields as a 32% protein diet for channel catfish raised in ponds from advanced fingerlings to marketable size at densities varying from 14,820 to 44,460 fish/ha under single‐batch cropping systems. Optimum dietary protein concentration for pond‐raised channel catfish does not appear to be affected by stocking density.     

Effects of Dietary Mycotoxins Produced by the Mold Fusarium moniliforme on Channel Catfish Ictalurus punctatus1

Channel catfish Ictalurus punctatus (initial weight: 6.1 g/fish) were fed eight diets containing the mold Fusarium moniliforme-cultured corn supplying 0.7, 2.5, 5, 10, 20, 40, 80, or 240 mg of the mycotoxin, fumonisin B₁ (FB₁)/kg diet under laboratory conditions for 12 wk. Fish fed diets containing FB₁ levels of 40 mg/kg and above showed reduced growth, feed consumption, and feed efficiency, but fish fed FB₁ concentrations of 20 mg/kg and below did not. The minimum level of FB₁ that depressed growth appeared to be between 20 and 40 mg/kg. Hematocrit was significantly lower for fish fed diets containing 80 and 240 mg FB,/kg than for fish fed diets containing lower levels of FB₁. Fish fed diets containing 40 mg FB₁kg and above had increased liver glycogen, increased vacuolation in nerve fibers, and perivascular lymphohistiocytic investment in the brain compared to fish fed diets containing lower levels of fumonisins. Results from this study indicate that FB₁ levels below 20 mg/kg diet are not a problem in commercial catfish feeds. However, it is prudent to screen for fumonisins in feed ingredients.     

Evaluation of Practical Diets with Various Levels of Dietary Protein and Animal Protein for Pond-Raised Channel Catfish Ictalurus punctatus1

Three levels of dietary protein (26, 28, or 32%) and four levels of animal protein (0, 2, 4, or 6%) were evaluated in a factorial experiment for pond-raised channel caffish using practical-type extruded feeds. Meat, bone, and blood meal (65% protein) was used as the animal protein source. Channel catfish fingerlings (average weight: 69 glfish) were stocked into 48 0.04-ha ponds at a rate of 24,700 fishha. Four ponds were used for each dietary treatment. Fish were fed once daily to apparent satiation for 158 d. No differences were observed in weight gain, feed consumption, feed conversion ratio, survival, and hematocrits of channel catfish fed diets containing various levels of dietary protein and animal protein. Inclusion of animal protein in the diet did not affect fish dressout, percentage visceral fat, or fillet composition. Comparison of means pooled by dietary protein without regard to animal protein showed that fish fed diets containing 26% protein had a lower percentage dressout than fish fed higher protein diets (55.4% vs. 56.3%). Fish fed the 32% protein diet had lower visceral fat than those fed the 26% or 28% protein diet (2.9% vs. 3.6% or 3.4%). Fillet fat was lower for fish fed the 32% protein diet than for fish fed the 26% protein diet (5.8% vs. 7.1%). Fillet fat in fish fed the 28% protein diet (6.5%) was not different from fish fed either 26% or 32% dietary protein. No differences were detected in fillet protein, moisture, and ash concentrations among fish fed diets containing various concentrations of protein. There were no interactions between dietary protein and animal protein for any variables. Results from the present study indicate that animal protein can be eliminated from diets for grow out of channel catfish fed to apparent satiation using diets containing 26% to 32% crude protein.     

Effects of Fungal Phytase on Utilization of Dietary Protein and Minerals, and Dephosphorylation of Phytic Acid in the Alimentary Tract of Channel Catfish Ictalurus punctatus Fed an All-Plant-Protein Diet

A feeding trial was conducted to quantify the effects of phytase at levels of 0, 500, 1,000, 2,000, 4,000, and 8,000 units (U) per kg diet on utilization of dietary protein and minerals by fingerling (12 g) channel catfish Ictalurus punctatus fed an all‐plant‐protein diet composed of soybean meal, corn, and wheat middlings. The effects of phytase on dephosphorylation of phytic acid (phytate) in the alimentary tract of catfish also were determined. After 14 wk, mean weight gains (30.2–43.9 g/fish), feed conversion ratios (2.27–2.40 g feed consumed/g weight gain), protein efficiency ratios (1.47–1.61 g weight gaid/g protein consumed), and dietary protein retentions (23.8–26.7%) did not differ significantly (P > 0.05) among treatment groups. A digestibility trial conducted after the feeding trial showed no difference (P > 0.05) in mean digestibility of diet dry matter (49.0–58.3%) or crude protein (85.4‐88.5%) among treatment groups. Concentrations of ash (46.7–48.6%), calcium (Ca, 17.9–18.5%), phosphorus (P, 9.1–9.5%), and manganese (Mn, 65.5–74.1 mg/kg) were significantly higher (P ≤ 0.05) in bone of fish fed ≥ 500 U/kg than in bone of fish fed 0 U/kg (ash, 43.5%; Ca, 16.4%; P, 8.4%; and Mn, 49.0 ma/kg), but concentrations of these minerals did not differ (P > 0.05) in bone of fish fed ≥ 500 Uk/g. The magnesium (Mg) content of bone did not differ (P > 0.05) between fish fed 0 U/kg (0.29%) or 500 U/kg (0.34%), but was significantly lower in fish fed 0 U/kg than in fish fed ≥ 1,000 U/kg (0.35–37%). Bone Mg levels did not differ (P > 0.05) among fish fed ≥ 500 U/kg. The amount of zinc (Zn) in bone of fish fed 8,000 U/kg (153.3 mg/kg) was significantly higher than that in fish fed 0 U/kg (115.7 mg/kg) or 500 U/kg (130.3 mg/ kg), but did not differ from Zn levels in bone of fish fed 1,000–4,000 U/kg (134.5–135.8 mg/ kg). Dephosphorylation of phytate occurred primarily in the stomach within 2–8 h after diet ingestion, depending on the level of phytase supplementation. Initial levels of total phytate in the diet decreased 32–94% in stomach contents of fish fed l,000–8,000 U/kg within 2 h after feeding. Eight hours after feeding, stomach contents of fish fed ≥ 1,000 U/kg contained less than 6% of initial total dietary phytate. Stomach contents of fish fed 500 U/kg retained 92% of initial total dietary phytate 2 h after feeding and 15% of total dietary phytate 8 h after feeding. Results of this study indicate that phytase supplementation at levels up to 8,000 U/kg diet did not increase weight gain or improve dietary protein utilization of channel catfish fed an all‐plant‐protein diet. Addition of phytase at a level of 1,000 U/kg diet was sufficient to significantly increase the Ca, P, Mg, and Mn content of bone, relative to fish fed an unsupplemented diet, and significantly decrease the quantity of total phytate in feces. A phytase level of 8,000 U/kg diet significantly increased the bioavailability of naturally occurring Zn in feed ingredients and increased the rate of phytate dephosphorylation in the stomach, compared with a diet containing no added phytase. Increased utilization of naturally occurring minerals in feed ingredients reduces the need for mineral supplements in diets and results in decreased elimination of minerals in feces. Thus, use of phytase in catfish feeds can be expected to provide both economic and environmental benefits.     

Effects of Dietary Protein Concentration and Feeding Regimen on Channel Catfish, Ictalurus punctatus, Production

A factorial experiment was conducted to examine effects of dietary protein concentration (24, 28, 32, or 36%) and feeding regimen (feeding once daily or every other day [EOD]) on channel catfish, Ictalurus punctatus, production in earthen ponds. Compared with fish fed daily, fish fed EOD had lower feed consumption, weight gain, net production, and percentage of market‐size fish but had high feed efficiency and required fewer hours of aeration. Fish fed EOD also had lower carcass yield, fillet yield, and visceral and fillet fat. There was a significant interaction between dietary protein and feeding regimen for weight gain. No significant differences were observed in weight gain of fish fed daily with diets containing various levels of protein, whereas weight gain of fish fed EOD with a 24% protein diet was lower than those fed EOD with higher protein diets. Results suggest that response of channel catfish to dietary protein levels depends on whether the fish were fed daily or EOD. Feeding EOD to satiation improved feed efficiency and required less aeration compared with fish fed daily but also reduced net production and processing yield; therefore, EOD feeding should be examined closely before implementation.     

美国红鮰鱼人工繁殖试验

从人工饲养的成鱼中挑选体色单纯、红色较深的个体作后备亲鱼进行强化培育，待其性腺发育成熟后，注射LHRH—A2催熟催产。催熟剂量为每千克鱼体重2～3μg(雄鱼不催熟)，催产剂量为8μg(雄鱼剂量减半)。试验结果，雌鱼的催产率达70．6％；共获受精卵大约18万粒；孵化出鱼苗约16万尾，平均孵化率88．9％；经培育，共获体长3．5cm的鱼种14．82万尾，鱼种的平均培育成活率达92．6％。试验结果表明，亲鱼培育是美国红鮰鱼人工繁殖取得成功的关键，而要获得遗传性状稳定的红鮰鱼鱼种，亲鱼的筛选至关重要；美国红鮰鱼生长快，抗病力强，产量高，肉质鲜嫩，是优良的养殖品种，可以在国内推广养殖。     

Comparison of Various Animal Protein Sources for Growth, Feed Efficiency, and Body Composition of Juvenile Channel Catfish Ictalurus punctatus

A laboratory study was conducted to compare different animal protein sources in diets containing 32% protein for channel catfish Ictalurus punrtatus . The experimental diets were practical-type diets and formulated to meet or exceed all known nutrient requirements for channel catfish. Twenty juvenile channel catfish (initial weight: 6.4 g/fish) were stocked into each of 25 110-L flow-through aquaria (five aquaria/treatment). Fish were fed twice daily to approximate satiation for 9 wk. Fish in each aquarium were counted and weighed collectively every 3 wk. No significant differences were observed in feed consumption, weight gain, feed efficiency, survival, percentages visceral fat and fillet yield, or proximate composition of fillets among channel catfish fed diets containing either 5% menhaden fish meal, meat and bone/blood meal, catfish by-product meal, poultry by-product meal, or hydrolyzed feather meal with supplemental lysine. The data indicate that these animal protein sources can be used interchangeably in diets for channel catfish without affecting fish growth, feed efficiency, or body composition.     

Effects of Dietary Vitamin E Enrichment on Frozen Channel Catfish, (Ictalurus punctatus) Fillets

The storage quality of channel catfish (Ictalurus punctatus), following long term frozen storage, fed diets containing 5 and 10 times the normal level of vitamin E for 45 or 60 days prior to harvest, was evaluated. There were no unusual effects of treatment on fish weight, survival or feed conversion ratios. Muscle vitamin E content was higher (P < 0.05) from fed diets containing supplemental vitamin E than in the control. Oxidation as measured by TBARS and sensory analysis values did not differ (P > 0.05) in response to vitamin E supplementation. Lipid oxidation increased as storage time increased. Lack of change in phospholipid and neutral lipid fractions during storage indicated that autoxidations was the major cause of oxidation in catfish. Vitamin E levels up to 10 times the normal amount did not improve the overall quality of catfish fillets.     

Evaluation of Corn Gluten Feed as a Dietary Ingredient for Pond-Raised Channel Catfish Ictalurus punctatus

Abstract.— This study was conducted to evaluate corn gluten feed as an alternative feedstuff in the diet of pond-raised channel catfish Ictalurus punctatus . Three 32%-protein diets containing 0%, 25%, or 50% corn gluten feed were tested. Channel catfish fingerlings (average weight: 57 g/fish) were stocked into 15 0.04-ha ponds at a rate of 18,530 fish/ha. Five ponds were used for each dietary treatment. Fish were fed to satiation once daily for a 147-d growing period. No differences were observed in feed consumption, weight gain, feed conversion ratio, survival, or fillet protein concentration among fish fed the test diets. Fish fed diets containing 25% and 50% corn gluten feed exhibited a lower level of visceral fat and a higher carcass yield than fish fed the control diet without corn gluten feed. The diet containing 50% corn gluten feed resulted in a lower level of fillet fat and a higher level of moisture than the control diet. There were no visible differences in the coloration of skin or fillet of channel catfish fed diets with and without corn gluten feed. Results from this study indicated that channel catfish can efficiently utilize corn gluten feed at levels up to 50%n without adverse effect on feed palatability, weight gain, or feed efficiency. Corn gluten feed may be beneficial in reducing fattiness of channel catfish and improving carcass yield by reducing the digestible energy to protein ratio of the diet.     

Masculinization of Channel Catfish Ictalurus punctatus by Oral Administration of Trenbolone Acetate

All-male populations of channel catfish, Ictalurus punelatus , were produced by feeding a diet containing trenbolone acetate to swim-up fry for 60 d. This hormone was effective in producing 100% males at doses of 50 to 150 mg/kg of diet. Fish that received 0 or 1 mg/kg of diet did not differ from the expected 1:1 sex ratio. Survival of control fish and fish fed diets containing trenbolone acetate were similar ( P > 0.05) at the end of the treatment period and after a 60-d grow-out period. Our results represent the first report of successful masculinization of channel catfish with a synthetic anabolic androgenic steroid.     

Effect of Exposure to Potassium Permanganate on Stress Indicators in Channel Catfish Ictalurus punctatus

Juvenile channel catfish Ictulurus punctatus were exposed to 1× (0.44 mg/L), 3× (1.32 mg/L), or 5× (2.19 mg/L) the recommended therapeutic concentrations of waterborne potassium permanganate (KMnO₄) for 36 h to determine the toxicity of the chemical. The fish were observed for 14 d after exposure. Gill, liver, and blood samples were collected before exposure, at 12, 24, and 36 h of exposure, and at 48-h intervals for 14 d thereafter. Analysis of homogenized gill tissue showed a transient increase in manganese content that quickly disappeared once exposure was discontinued. Fish exposed to the 3× and 5× concentrations of KMnO₄ experienced 9 and 50.6% mortality, respectively. Plasma cortisol was elevated more than ten-fold at the 5× concentration. Both plasma chloride and osmolality were significantly reduced at the 3× and 5× concentrations but were unchanged at the 1×. Packed cell volumes (PCV) of whole blood rose significantly in response to 3× and 5× concentrations of KMnO₄ Mortality may have been the result of blood electrolyte depletion as indicated by increased PCVs, loss of chloride, and reduced osmolality. All stress indicators measured, except PCV at the 5× concentration, were indistinguishable from unexposed controls within 48 h after exposure was discontinued. At the l× concentration (the concentration most like that employed in a disease treatment) no changes were observed in any stress indicators measured suggesting that KMnO₄ may be safely used as a disease therapeutant for channel catfish.     

Phosphorus Availability of Common Feedstuffs to Channel Catfish Ictalurus punctatus as Measured by Weight Gain and Bone Mineralization1

The efficacy of using weight gain and bone mineralization to estimate phosphorus availability from feed ingredients for channel catfish was investigated at the conclusion of a 12-wk feeding trial. Juvenile channel catfish (initial weight = 7.8 g/fish) were fed one of seven test diets each containing phosphorus from a single source. All diets were isocaloric, isonitrogenous, and met all nutrient requirements of channel catfish except for phosphorus, which was assumed to be the factor limiting growth. Phosphorus was considered to be 90% available to fish fed the diet containing monosodium phosphate, but a relative value of 100 was assigned to this treatment for purposes of comparison. All other availability values were calculated relative to this value. Phosphorus availabilities (based on weight gain) for wheat middlings, cottonseed meal, and soybean meal were 38%, 43%, and 49%, respectively, which are in the range previously reported for channel catfish. Phosphorus availability values (based on weight gain) for dicalcium phosphate, menhaden fish meal, and meat and bone/blood meal were 82%, 75%, and 84%, respectively. These values were considerably higher (93–96%) than previously reported for catfish when based on bone ash or bone phosphorus. However, availability data based on weight gain for feedstuffs of animal origin generally agreed with phosphorus availability data reported for rainbow trout. Based on our data, mineral utilization by animals in general, and on known physiology of channel catfish, we suggest that weight gain may be a reliable indicator of phosphorus availability and that phosphorus availability values may be overestimated when base on bone mineralization.     

斑点叉尾(鮰)养殖技术及病害防治

我国自美国引进斑点叉尾(鮰),并深入进行了养殖技术研究,已在全国20多个省、市、自治区推广应用,十几年来产值达数十亿元.斑点叉尾(鮰)病害及防治技术的研究,解决了养殖中重大技术难点,它的应用取得了巨大经济效益和社会效益.