Aflatoxins from Moldy Corn Cause No Reductions in Channel Catfish Ictalurus punctatus Performance

Aflatoxins are a group of mycotoxins produced by the mold organisms Aspergillus flavus and A. parasiticus on feed grains and oil seeds such as corn, peanuts, and cottonseed. Research conducted in aquaria, about 15 yr ago, demonstrated that channel catfish Ictalurus punctatus are very tolerant to dietary aflatoxin B₁ (AFB₁) from a purified source. To evaluate the effect of feeding diets containing aflatoxin from a natural source, moldy corn (MC) naturally contaminated with a high concentration (550 pg/kg) of total aflatoxins was incorporated into practical diets. The diets were fed to Juvenile catfish in two experiments. Experiment 1 consisted of feeding catfish (mean body weight 7.1 g/fish) four diets containing 20% or 40% of two lots of corn; one with no apparent mold contamination, which was designated as clean corn (CC), or the previously described MC. Each diet was fed twice daily to five 100-L aquaria of 20 fish each for 12 wk. Experiment 2 consisted of three diets containing either 50% CC or MC, or a combination of 25% CC and 25% MC prepared by the cooker-extrusion method. Each diet was fed once daily for 130 d to five replicate 0.04-ha ponds of catfish fingerlings. Results of these experiments indicate that feeding diets containing aflatoxin from moldy corn does not affect channel catfish weight gain, feed consumption, feed efficiency, survival, hematocrit, or hepatosomatic ratio. No liver abnormalities were observed upon gross examination. Levels of aflatoxin were reduced approximately 63% in the diets used in experiment 2 after exposure to the high temperature (ca. 120 C) of the cooker-extrusion process used to manufacture commercial catfish diets.     

Reproductive Performance of Pigmented and Albino Female Channel Catfish Induced to Spawn with HCG or Ovaprim

Reproductive performance of albino and pigmented channel catfish ( Ictalurus punctarus ) females was compared when spawning was induced with HCG (human chorionic gonadotropin) or Ovaprim ³ (domperidone and [d-Ala⁶, Pro⁹ NEt]-luteinizing hormone-releasing hormone). In 1985, only HCG was used to induce spawning. Albino females required more injections, had a longer latency period from time of first injection to spawning, and had lower spawning success (30%) than pigmented females (77%). No differences were observed between albino and pigmented females for time-of-day of spawning, number of eggs obtained by manual stripping, and number of eggs/kg body weight. In 1988, HCG, Ovaprim, and saline (control) were used to induce spawning. HCG induced spawning in 80% of albino and 71% of pigmented females. Ovaprim induced 67% of pigmented females to spawn, but only 2 of 5 albino females spawned. One of four pigmented females injected with saline spawned. Albino females yielded 40–50% fewer eggs/kg body weight than pigmented females. Other performance characteristics for albino and pigmented females were similar whether injected with HCG or Ovaprim. High temperatures encountered during the 1985 spawning season my have had a differential effect on albino and pigmented fish and may account for some differences in spawning success.     

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.     

Re-evaluation of vitamin E supplementation of practical diets for channel catfish, Ictalurus punctatus, production

A 10-month feeding trial was performed with channel catfish, Ictalurus punctatus , to re-evaluate the minimum level of dietary vitamin E supplementation required under conditions of commercial production. Four levels (0, 15, 30 and 60 mg kg⁻¹ diet) of supplemental vitamin E were added as DL -α-tocopherol acetate to a typical commercial catfish diet. Sixteen 0.04-ha ponds were stocked in July, at a rate of 25 000 fish ha⁻¹, with two size classes (averaging 18 and 265 g fish⁻¹) of fingerling channel catfish, and each diet was fed to fish in four replicate ponds once daily to satiation. After 10 months of feeding, a total harvest was performed to obtain final production data, and samples were obtained from fish in all ponds. Liver and plasma samples were obtained for α-tocopherol determination, and liver, heart and muscle samples were processed for histological evaluation.
No discernible differences occurred among fish fed the different diets with respect to weight gain or survival. Mean production rate was 9734 kg ha⁻¹, with a final average fish weight of 0.53 kg. A significant ( P < 0.05) effect of diet was noted in plasma and liver α-tocopherol levels, which increased with dietary supplementation. An effect of size also was apparent, with plasma and liver α-tocopherol levels being higher in larger fish compared with smaller fish within a dietary treatment. Histological evaluation revealed no differences among fish fed the different dietary treatments. Based on the lack of overt histological signs of deficiency, it appears that the current level of vitamin E supplementation of commercial catfish diets may be reduced considerably with no detriment to channel catfish health or production.     

A Practical Calcium Hardness Criterion for Channel Catfish Hatchery Water Supplies

Three pairs of brood channel catfish Ictalurus punctatus were induced to spawn in aquaria supplied with flowing water from a reservoir filled with ground water (calcium hardness = 110 mg/L as CaCO₃= 44 mg/L as calcium). Fertilized egg masses were allowed to incubate in aquaria for 6 h and each mass was then split into five portions. The five portions were then allowed to hatch and the resulting sac fry developed in waters with calcium hardnesses of 0, 1, 5, 10, or 100 mg/L as CaCO₃ (0, 0.4, 2, 4, or 40 mg/L as calcium). Test waters were prepared from distilleddeionized water and reagent-grade chemicals; tests were conducted using static-renewal conditions. Survival from hatch to onset of exogenous feeding ("swim-up") averaged 62% in calcium-free water and 98% at all other calcium hardness levels. Wet weight gain, dry weight loss, and resistance to environmental hypoxia were significantly affected ( P < 0.05) by environmental calcium levels: best growth, yolk utilization rate (indicated by changes in dry weight and visual observation), and tolerance to low dissolved oxygen concentrations were found at calcium hardnesses of 10 and 100 mg/L as CaCO₃. Based upon these results, a minimum calcium hardness of 10 mg/L as CaCO₃ (4 mg/L as calcium) is recommended for channel catfish hatchery water supplies.     

Evaluation of Various Concentrations of Dietary Protein and Animal Protein for Pond-Raised Channel Catfish Ictalurus punctatus Fed to Satiation or at a Restricted Rate

A factorial experiment was conducted to evaluate effect of dietary protein (28% or 32%), animal protein (0, 3, or 6%), and feeding rate (satiation or >90 kg/ha per d) on production characteristics, processing yield, and body composition of pond-raised channel catfish Ictalurus punctatus . Fingerling channel catfish (average weight: 55 g/fish) were stocked into 60, 0.04-ha ponds at a rate of 18,530 fish/ha. Five ponds were used for each dietary treatment. Fish were fed once daily to satiation or no more than 90 kg/ha per d for 147 d. Fish fed at a rate of >90 kg/ha per d consumed about 85% of the amount of feed consumed by fish fed to satiation. Dietary protein did not affect the total amount of feed fed, amount of feed consumed per fish, weight gain, feed conversion efficiency, or fillet protein. Animal protein had no effect on the total amount of feed fed, amount of feed consumed per fish, weight gain, or fillet protein and ash. Fish fed a diet containing 6% animal protein converted feed more efficiently than fish fed diets containing 0% and 3% animal protein. Fish fed to satiation daily consumed more feed, gained more weight, converted the feed less efficiently, and had a higher carcass yield, a higher level of visceral fat as compared to fish fed at a rate of >90 kg/ha per d. Feeding rate had no effect on fillet protein. Results from this study indicated that both a 28% and a 32% protein diet with or without animal protein provided the same growth rate of channel catfish raised in ponds from fingerlings to marketable size if feed is not restricted below a maximum rate of 90 kg/ha per d. Even though there were some interactions among the three factors evaluated, dietary protein levels of 28% to 32% and animal protein levels of 0% to 6% do not appear to markedly affect carcass yield and fillet proximate composition of pond-raised channel catfish.     

Palatability of Sarafloxacin HCl-Medicated Feed to Channel Catfish

Two experiments were conducted to evaluate the palatability of sarafloxacin HCl to channel catfish, Ictalurus punctatus. Fingerling channel catfish were raised in 110-1 glass aquaria supplied with flowing well water at a rate of 1 l/min. Fish were fed to satiation once daily either a purified or a practical diet formulated to contain 0, 500, 1,000, 2,000, or 4,000 mg active sarafloxin HCl/kg of diet. Feed consumption was quantified daily for 5 days. All fish were weighed at the beginning and at the end of each experiment. There was a significant decrease in feed consumption of fish fed purified diets with increasing levels of sarafloxacin HCl. However, feed consumption was adequate to provide the proposed dosage regardless of drug concentration. Fingerling channel catfish readily consumed practical diets containing sarafloxacin HCl; feed consumption and weight gain of fish fed medicated and non-medicated practical diets did not differ. There were no apparent palatability problems that would negate use of sarafloxacin HCl in commercial channel catfish feeds.     

Nutritional value of frass from black soldier fly larvae,Hermetia illucens,in a channel catfish,Ictalurus punctatus,diet

Frass is the by‐product of the larval meal industry and includes larval waste, exoskeleton sheds and residual feed ingredients. Experimental frass was derived from the larvae of black solder flies fed distillers' dried grains with solubles and had a protein and fat content of 216 and 60 g/kg, respectively. A 10‐week study was conducted to evaluate the effect of dietary levels of frass on growth, feed utilization, and body proximate and mineral composition of channel catfish, Ictalurus punctatus. Five diets containing 0, 50, 100, 200 and 300 g frass per kg diet were fed to channel catfish (5.24 ± 0.04 g) in quadruplicate aquaria to apparent satiation twice daily. Final weight gain was significantly increased in fish fed diets containing frass at levels from 100 to 300 g/kg. Fish fed diets without frass, and with 300 g/kg frass, showed the lowest and highest feed intake, respectively. Feed and protein efficiencies, however, were significantly lower in fish fed frass at levels of 200 g/kg and higher compared to the control diet. Survival, whole‐body composition and mineral content were not affected by frass. In summary, black soldier fly larval frass has potential as a protein source or just an ingredient for enhancing palatability of catfish diets.     

Comparative growth and yield of channel catfish and channel × blue hybrid catfish fed a full or restricted ration

Growth and yield (kg ha^?1) of the channel catfish (Ictalurus punctatus, Rafinesque, 1818) and the channel × blue hybrid catfish [I. punctatus female ×I. furcatus (Lesueur, 1840) male], which shared the Jubilee strain of channel catfish as the maternal parent, were compared in sixteen 0.1 ha earthen ponds (14 852 fish ha^?1) during the April to November growing season. Each fish genetic group was fed a commercially formulated 32% protein feed daily to apparent satiation or at 80% of the mean daily satiation ration. Net yield and individual weight were higher for channel × blue hybrid catfish compared with channel catfish and for fish fed a full ration compared with a restricted ration. When fed a full ration, the channel × blue hybrid catfish grew faster from May to September than did the purebred channel catfish because the hybrid catfish consumed a greater percentage of its body weight at each feeding. Net yield within each fish genetic group was lower when feed ration was restricted. The per cent reduction in net yield in response to feed restriction was similar for each fish genetic group.     

Effect of Dietary Protein Concentration and Feeding Rate on Weight Gain,Feed Efficiency,and Body Composition of Pond-Raised Channel Catfish Ictalurus punctatus1

Two experiments were conducted in earthen ponds to evaluate the effect of dietary protein concentration and feeding rate on weight gain, feed efficiency, and body composition of channel catfish. In Experiment 1, two dietary protein concentrations (28% or 32%) and four feeding rates (≤ 90. ≤ 112, ≤ 135 kg/ha per d, or satiation) were used in a factorial arrangement. Channel catfish Ictalurus punctatus fingerlings (average size: 27 g/fish) were stocked into 0.04-ha ponds at a rate of 24,700 fish/ha. Fish were fed once daily at the predetermined maximum feeding rates for 282 d (two growing seasons). In Experiment 2, three dietary protein concentrations (24, 28, or 32%) and two feeding rates (≤ 135 kg/ha per d or satiation) were used. Channel catfish (average size: 373 g/fish) were stocked into 0.04-ha ponds at a rate of 17,300 fish/ha. Fish were fed once daily for 155 d. In both experiments, five ponds were used for each dietary treatment. Results from Experiment 1 showed no differences in total feed fed, feed consumption per fish, weight gain, feed conversion ratio (FCR), or survival between fish fed diets containing 28% and 32% protein diets. As maximum feeding rate increased, total feed fed, feed consumption per fish, and weight gain increased. There were no differences in total feed fed, feed consumption per fish, or weight gain between fish fed at ≤ 135 kg/ha per d and those fed to satiation. Fish fed the 28% protein diet had a lower percentage carcass dressout and higher percentage visceral fat than fish fed the 32% protein diet. Dietary protein concentrations of 28% or 32% had no effect on fillet protein, fat, moisture, and ash. Feeding rate did not affect FCR, survival, percentage carcass dressout, or fillet composition, except fillet fat. As feeding rate increased, percentage visceral fat increased. Fish fed at ≤ 90 kg/ha per d had a lower percentage fillet fat than fish fed at higher feeding rates. In Experiment 2, dietary protein concentration or maximum feeding rate did not affect total feed fed, feed consumption per fish, weight gain, FCR, or survival of channel catfish. Feeding rate had no effect on percentage carcass dressout and visceral fat, or fillet composition. This was due to the similar feed consumption by the fish fed at the two feeding rates. Fish fed the 24% protein diet had lower carcass dressout, higher visceral fat and fillet fat than those fed the 28% or 32% protein diet. Results from the present study indicate that both 28% and 32% protein diets provide satisfactory fish production, dressed yield, and body composition characteristics for pond-raised channel catfish fed a maximum rate of 90 kg/ha per d or ahove.     

Effects of Seasonal Variations, Thyroid and Steroid Hormones, and Carp Pituitary Extract on the Artificial Production of Channel Catfish Ictalurus punctatus× Blue Catfish I. furcatus Hybrids

The primary objective was to compare thyroid hormones and levels of carp pituitary extract for the artificial production of female Ictalurus punctatus × male I. furcatus hybrid catfish. The effects of different carp pituitary extract dosage rates (5, 6, 9, and 10 mg/kg), carp pituitary extract (6 and 10 mg/kg) supplemented with the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃), or pregnenolone (DHP) were determined for inducing ovulation of female channel catfish, fertilization of channel catfish eggs with male blue catfish sperm, and hatching rate of these embryos. Hormone treatments thyroxine and tri-iodothyronine with carp pituitary extract, carp pituitary extract alone, and pregnenolone with carp pituitary extract used to artificially produce hybrid catfish were not different in terms of ovulation rates, eggs/kg, fry/kg body weight of female channel catfish, fertilization rates, or hatching rates (P > 0.05). These findings suggest that lower amounts of carp pituitary extract may be used to induce spawn of female channel catfish for production of channel-blue catfish hybrids and the addition of thyroid and steroid hormones is ineffective at the rates used in this study.     

Effects of Periodic Feed Deprivation on Growth, Feed Efficiency, Processing Yield, and Body Composition of Channel Catfish Ictalurus punctatus

Two studies were conducted in 110‐L flow‐through aquaria and 0.4‐ha ponds to evaluate effects of periodic feed deprivation on the growth performance of channel catfish Ictalurus punctatus. Fish were deprived of feed 0, 1, 2, or 3 consecutive d/wk, l d per 5‐d period, or 3 consecutive d per 10‐d period and fed to satiation on days fish were fed. In Experiment 1, fish fed less frequently than daily consumed significantly less feed (over the experimental period) and gained significantly less weight than fish fed daily, except that feed consumption of fish deprived of feed 1 d/wk was not significantly different from that of fish fed daily. Compared with fish fed daily, fish deprived of feed 2 d/wk had significantly lower feed conversion ratio (FCR). Visceral fat of fish deprived of feed 1 or 2 d/wk was similar to that of fish fed daily, but fish deprived of feed for longer periods had significantly lower visceral fat than fish fed daily. Regression analysis indicated that feed consumption, weight gain, and visceral fat increased linearly as the number of days that fish were fed increased. In Experiment 2, there were no significant differences in the amount of feed fed between fish deprived of feed 1 d/wk and those fed daily. Net production of fish deprived of feed 1 or 2 d/wk or 1 d per 5‐d period was not significantly different from that of fish fed daily, but fish deprived of feed for longer periods had significantly lower net production than fish fed daily. Visceral fat of fish deprived of feed 1 d/wk or 1 d per 5‐d period was similar to that of fish fed daily, but fish on other treatments had significantly lower visceral fat than fish fed daily. Regression analysis showed that as the number of days fed increased the amount of feed fed and net production increased quadratically. Feed conversion ratio, carcass yield, visceral fat, and fillet fat increased, while fillet moisture decreased linearly as the number of days fed increased. Although feeding less frequently than daily may improve feed efficiency, and fish deprived of feed may demonstrate compensatory growth when a full feeding regime is resumed, it may be difficult to provide enough feed to satiate all size‐classes of fish under a multiple‐batch cropping system without causing water quality problems. Under normal economic conditions, fish should be fed daily to apparent satiation without waste and without causing water quality problems. However, during periods of unfavorable economic conditions, channel catfish raised from advanced fingerlings to market size may be fed less frequently than daily to reduce production cost. Results from the present study indicated that feeding channel catfish to satiation 5 or 6 d/wk (not feeding on one or two weekend days) could provide some benefits in reducing production cost through reduced feed and labor costs for food‐sized channel catfish during periods of low fish prices and high feed prices.     

Differences in Growth in Blue Catfish Ictalurus furcatus and Channel Catfish Z. punctatus Fed Low-Protein Diets With and Without Supplemental Methionine and/or Lysine

Three feeding experiments were conducted to evaluate growth and body composition in blue caffish Ictalurus furcatus or channel caffish I. punctatus when fed diets containing 22% protein with or without supplemented methionine and/or lysine. All experiments were conducted in 110‐L aquaria that were part of a recirculating system. In Experiment 1,15 juvenile blue catfish (2.7 g) were randomly stocked into aquaria and fed one of three diets containing different (22%, 27%, and 32%) percentages of protein. Fish were fed twice daily to excess for 10 wk. In Experiment 2, juvenile blue catfish (5.4 g) were randomly stocked into aquaria and fed one of six diets containing either 22% (diet 1) or 32% (diet 2) protein. The diet containing 22% protein (diet 1) had either 0.3% crystalline L‐methionine (diet 3), 0.4% crystalline L‐lysine (diet 4), or 0.3% L‐methionine + 0.4% L‐lysine (diet 5) added. A sixth diet was formulated to contain 32% protein and 0.2% crystalline L‐methionine. Fish were fed in excess for 12 wk. In Experiment 3, juvenile channel caffish (10.3 g) were stocked and fed diets 14 from Experiment 2, twice daily in excess for 8 wk. In Experiment 1, after 10 wk, final individual weight, weight gain (%), and specific growth rate (SGR) of blue catfish fed diets containing three protein levels were not significantly different (P > 0.05) and averaged 12.9 g, 378%, and 2.2%/d, respectively. Fish fed the diet containing 27% protein had higher (P < 0.05) whole‐body protein (65.4%) compared to fish fed diets containing either 22% or 32% protein. In Experiment 2, final weight, weight gain (%) and SGR of blue catfish were not significantly (P > 0.05) different among diets and averaged 24.7 g, 355%, and 1.8%/d, respectively. Percentage whole‐body protein and lipid were not significantly (P > 0.05) different between fish fed diets containing 22% or 32% protein. In Experiment 3, channel caffish fed a diet containing 32% protein had significantly (P > 0.05) higher final individual weight, weight gain (%), and SGR compared to fish fed diets containing 22% protein, with and without supplemental methionine or lysine. Results indicate that blue catfish may be able to utilize a diet with 22% protein, and that addition of crystalline methionine and/or lysine did not improve growth. However, channel catfish grown in aquaria did not appear to have similar growth when fed a diet containing 22% protein compared to fish fed 32% protein, even when supplemental methionine or lysine was added. Further research on blue catfish and the use of a low‐protein diet (22% protein) needs to be conducted in ponds.     

Induced Spawning of Wild American Shad Alosa sapidissima Using Sustained Administration of Gonadotropin-Releasing Hormone Analog (GnRHa)

American shad Alosa supidissima broodstock were collected from the Susquehanna River during their spawning migration. Mean volume of expressible milt (± standard deviation) was 2.5 (±1.7) mL/kg body weight; mean spermatozoid count was 66.2 ± 10⁹ (±163 ± 10⁹) spermntozoa/mL; and duration of 50% motility was 36.5 (±10.3) see. Ovarian biopsies indicated the presence of oocytes of various sizes (200–2,000 μm in diameter) and stages of development. Fish were implanted with a delivery system loaded with gonadotropin-releasing hormone analog (GnRHa) and started spawning 2 d after treatment. Fertile eggs were collected daily for the next 9 d, for a total of 50,100 eggs/kg body weight with a mean fertilization success of 62%. Upon cessation of spawning, the ovaries of all females still contained large numbers of oocytes at various stages of development, as at the beginning of the experiment, but with a greater number of atretic oacytes. Our observations show that American shad have an asynchronous ovarian development, and treatment with a GnRHa delivery system is effective in inducing several successive spawns of fertile eggs.     

Induced Final Maturation and Spawning of the Marbled Grouper Epinephelus microdon Captured from Spawning Aggregations in the Republic of Palau, Micronesia

A high percentage (98.3%, N = 60) of the marbled grouper Epinephelus microdon individuals captured from spawning aggregations during July and August 1993 in the waters surrounding the island of Koror, Republic of Palau, Micronesia, were in the stage of maturity at which final maturation and spawning could be hormonally induced. The sex ratio of the captured fish was highly skewed towards males (4 male:1 female). Sexually immature females comprised the smallest size class, (<0.6 kg body weight (BW) or 33.0 cm total length (TL)), while sexually mature females were restricted to the 0.6–1.5 kg BW (33.0–46.4 cm TL) groups. Males predominated in size classes >0.6 kg BW, and individuals >1.5 kg BW (46.4 cm TL) were exclusively male. All females with oocytes that averaged ( N = 50) >400 μm in diameter were successfully induced to spawn by a two-injection protocol using human chorionic gonadotropin (HCG) at total dosages of 2,100–3,200 IU/kg fish. All males used in the spawning trials were administered a single injection of HCG at dosages of 500 or 1,000 IU/kg fish. Fecundity ranged between 7.96 × 10⁵−1.24 × 10⁶kg BW, average spawned egg diameters ranged between 769–832 μm, percent fertilization ranged between 32.6%–99.9%, and hatching percentages were >90.0%. Total fat content of eggs obtained from a pooled spawning event was 14.1 mg/100 mg dry weight. The data indicate that HCG is a suitable treatment for the induction of spawning in marbled grouper females that possess a mean oocyte diameter of 400 μm or greater.     

Restricted and Satiate Feeding of Two Genetically Isolated Strains of Juvenile Channel Catfish Ictalurus punctatus Reared on 28% and 32% Protein Diets

A 10-wk growth comparison trial of two strains of channel catfish Ictalurus punctatus was conducted in 40 120-L flow-through aquaria using a 2 ± 2 × 2 factorial experiment design. The three factors evaluated were: strain (Norris and NWAC103), dietary protein level (28% and 32%), and feeding rate (restricted and satiate). Average initial weight (× SD) for the Norris strain was 3.0 ± 0.08 g/fish, while that of the NWAC103 strain was 4.7 ± 0.13 g/fish. The feeding rate for the satiated group was adjusted based on feeding observations. The feeding rate for the restricted group was adjusted to about ²/₃ of the satiate level. For both satiate and restricted feeding regimens, the NWAC103 strain consumed more feed than the Norris strain. Fish of Norris strain fed the 32% protein diet consumed more feed than fish fed the 28% protein diet; however, there were no differences in feed consumption in the NWAC103 fish fed the two protein diets. Regardless of feeding rate, the NWAC103 fish gained more weight and converted feed more efficiently than the Norris fish. Fillet composition was not affected by fish strain. Fish fed the 28% protein diet had a lower level of fillet protein than fish fed the 32% protein diet. In fish fed to satiation, a 32% protein diet resulted in a lower fillet fat level than a 28% protein diet, but no differences were observed in fillet fat levels between fish fed the two dietary protein levels for the restricted group. Results from the present study demonstrate that under laboratory conditions, the NWAC103 strain of channel catfish is superior to Norris strain in feed consumption, growth rate, and feed efficiency. Our data also indicate that either a 28% or 32% protein diet can be fed to either strain of channel catfish whether they are fed to satiation or fed a restricted ration with no detrimental effects on growth.     

Evaluation of Experimental and Practical Diets for Bluegill Lepomis macrochirus and Hybrid Bluegill L. cyanellus × L. macrochirus

Two experiments were conducted to identify appropriate experimental and practical diets for bluegill Lepomis macrochirus and hybrid bluegill L. cyanellus × L. macrochirus reared in aquaria. In the first study, four experimental diets and five commercial diets were evaluated in juvenile hybrid bluegill initially weighing 4.8 g/fish. The experimental diets contained casein (CAS), casein + gelatin (CAWGEL), casein + L‐arginine‐HCI (CAS/ARG), or casein + gelatin + crystalline amino acids (CAS/AA) as sources of crude protein. The commercial diets included three diets formulated to meet the nutritional requirements of rainbow trout Oncorhynchus mykiss and two diets formulated to meet the nutritional requirements of channel catfish Ictalurus punctatus. Each diet was fed twice daily at a rate of 4% of body weigh/d to triplicate groups of fish. At the end of the 8‐wk feeding trial, weight gain was significantly higher in fish fed the best commercial rainbow trout diets (205–217%) compared to fish fed diets formulated for channel catfish (87–104%). Weight gain and feed efficiency (FE) of fish fed the experimental diets (5346% and 0.19–0.32, respectively) were significantly lower than those of fish fed the commercial rainbow trout diets (143–217% and 0.49–0.64, respectively). In the second experiment, the same dietary treatments were fed for 8 wk to juvenile bluegill initially weighing 3.7 g/fish. Each diet was fed twice daily at a rate of 4% of body weight/d to triplicate groups of fish. Weight gain was significantly higher in fish fed commercial trout diets (291–402%) compared to fish fed diets formulated for channel catfish (164–191%). Weight gain and FE of fish fed CAS/ARG were significantly higher than those of fish fed the commercial catfish diets, but significantly lower than those of fish fed the best commercial trout diets. Results of this study indicate that commercial rainbow trout diets are preferable to commercial channel catfish diets for culture of bluegill and hybrid bluegill. More research is needed to identify appropriate experimental diets for this group of fishes.     

Effects of Feeding Time and Frequency on Growth of Channel Catfish Ictalurus punctatus in Closed Recirculating Raceway Systems

Abstract.– Experiments were conducted to evaluate the effects of feeding time and frequency on the growth, survival, feed conversion, and body composition of channel catfish Ictalurus punctatus cultured in closed recirculating raceway systems. In separate experiments, two stocking sizes (18 and 232 g/fish) of channel catfish were examined. Treatments consisted of 1) feeding catfish once daily, 3% of body weight at 0800 h; 2) feeding catfish once daily, 3% of body weight at 1200 h; 3) feeding catfish once daily, 3% of body weight at 1700 h; and 4) feeding catfish three times daily, 1% of body weight at 0800 h, 1200 h, and 1700 h. Weight gain, specific growth, feed conversion, percentage survival, and fillet proximate composition of channel catfish among treatments did not differ ( P > 0.05). The percentage visceral fat of channel catfish fed the single meal at 0800 h was significantly lower (P < 0.05) than channel catfish receiving multiple feedings, but was not different than the visceral fat content of channel catfish fed at 1200 h and 1700 h. Under the conditions of this study, results indicate neither feeding time or feeding frequency significantly influences the growth, survival, and body composition of channel catfish raised in closed recirculating raceway systems.     

Evaluation of Dual Injection of LHRHa and the Dopamine Receptor Antagonist Pimozide in Cage Spawning of Channel Catfish Ictalurus punctatus

Abstract.— Control of reproduction in cultured fishes has been improved by the use of gonadotropin releasing hormones (GnRH's) and, in many fishes, the use of dopamine (DA) receptor antagonists. However, little successful use of these treatments has been reported for channel catfish Ictalurus punctatus . This study was conducted to investigate the potential of treatment with a gonadotropin hormone releasing hormone (GnRH) and a dopamine (DA) receptor antagonist to improve cage spawning success in channel catfish. Two and 3-yr-old catfish were selected from ponds. All males were injected with des-Gly¹⁰, [D-Ala⁶]-Leuteinizing hormone releasing hormone ethylamide (LHRHa, 50 μg/kg body weight). Females were randomly assigned to the various injection treatments, control (vehicle injected, C), LHRHa only (L), DA receptor antagonist (pimozide) only (P), and LHRHa and pimozide (LP). After injections, one male and one female were paired and placed into 1 m wide × 1.5 m long × 1.2 m deep spawning cages with a metal spawning can. Spawning cans were checked from 1 to 10 d after injection and successful spawning events were recorded. Five trials were conducted between 13 May and 5 June 1998. The LP treatment yielded significantly more spawns than any other treatment (LP, N = 24, 83% > L, N = 25, 44% > C, N = 23, 43 % > P, N = 11, 36%). The greatest promotion of spawning with LP treatment was in the first two induction trials. In the subsequent three trials, differences between treatments were not significant, although LP tre.ated females tended to spawn more frequently. Percent hatch (60.5 ± 3.4%) did not differ between treatments. Treatment of females with LHRHa + pimozide is a potentially useful method for increasing spawning success, particularly early in the spawning season.     

The Effect of Luteinizing Hormone Releasing Hormone Analog Regime and Stage of Oocyte Maturity for Induced Ovulation of Channel Catfish,Ictalurus punctatus

This study addresses rapid methods to identify mature channel catfish, Ictalurus punctatus, females for induced spawning with luteinizing hormone releasing hormone analog (LHRHa) and common carp pituitary extract (CPE) and the effects of stage of maturity, hormone dose, season, and cannulation before hormone injection. Hormonal intervention is the most effective method for inducing maturation and spawning in channel catfish × blue catfish, Ictalurus furcatus, hybrids. A total of 80 mature channel catfish were staged for maturity based on secondary sexual characteristics and 20–30 oocytes cannulated to ascertain their maturation stage based on the position of gonadal vesicle. Twenty females were randomly assigned to one of the four hormone regimes (priming + resolving dose): CPE 2 + 8 mg/kg (CPEC); LHRHa 20 + 40 µg/kg (LHRHaL); LHRHa 20 + 60 µg/kg (LHRHaM); and LHRHa 20 + 80 µg/kg (LHRHaH) and a fifth treatment consisted of 20 females selected based on apparent maturity as evidenced by external appearance were injected with CPE, 2 + 8 mg/kg without cannulation (CPEO). Two trials were conducted in early part of the spawning season and two trials in peak season. External methods to identify maturity correlated (r = 0.63) with that of “germinal vesicle position” method to identify the stage of maturity in females. Mean percent of females that ovulated, hatched, and fry produced per kg body weight did not differ (P > 0.05) among the five hormone treatments. The mean percent females that ovulated was higher (P < 0.05) for CPE‐induced females that were identified as “excellent” females based on external examination. The performance of cannulated females did not differ (P > 0.05) with that of non‐cannulated catfish. The mean egg quality of hormone‐induced females and percent of females ovulated in response to hormone treatment established a weak but significant linear relationship (Y = 3.85 + 0.008 × ovulation, r² = 0.39, P < 0.05).