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.     

Low-Quality Diets for Growout of Channel Catfish,Ictalurus punctatus

Abstract

A feeding trial was conducted to evaluate low-quality diets for growout of pond-raised channel catfish. Five practical diets containing various levels of protein (10-28%) of varying quality (with or without animal protein and/or soybean meal), and with or without certain nutrient supplements (vitamin, minerals, lysine, or fat) were fed to channel catfish, Ictalurus punctatusstocked in 0.04-ha earthen ponds at a rate of 17,290 fish/ha. The diets were as follows: (1) 28% protein, nutritionally complete control; (2) 28% protein without supplemental vitamins, minerals, or fat; (3) 18% protein + supplemental lysine, vitamins, and minerals, but without animal protein; (4) 10% protein without animal protein, soybean meal, or supplemental vitamins and minerals; and (5) 10% protein + supplemental lysine, vitamins, and minerals, but without animal protein or soybean meal. Each diet was fed once daily to apparent satiation to fish in five replicate ponds for a single growing season. Fish fed diets containing 18% or 28% protein without supplements had similar diet consumption rates and weight gain as those fed the 28% control diet, but the fish fed the control diet converted diet more efficiently. Fish fed the 10% protein diet without supplements consumed less diet, converted diet less efficiently, and gained less weight than fish fed diets containing higher levels of protein. The addition of supplements to the 10% protein diet increased weight gain and processing yield as compared to fish fed the 10% protein diet without supplements. Body fattiness increased, fillet protein decreased, and carcass, fillet and nugget yields decreased as dietary protein decreased. The data show that pond-raised channel catfish can be grown effectively on a diet containing 18% protein that is of relatively low quality, but fattiness is increased and processing yield is decreased. However, because of the negative aspects of this diet, we would not recommend it for general use in commercial catfish culture. It could be used where fattiness and processing yield are not of consequence, such as recreational ponds. For that matter, the 10% diet without supplements could be used as well in these situations if maximum growth is not desired.     

Use of Corn Germ Meal in Diets for Pond‐Raised Channel Catfish,Ictalurus punctatus

Corn germ meal (CGM) is a by‐product of corn milling. On the basis of its nutrient composition and digestibility values, it appears to be a suitable ingredient for use in channel catfish, Ictalurus punctatus, diets. A study was conducted to examine the use of various levels of CGM in diets for pond‐raised channel catfish. Four 28% protein diets containing 0, 15, 25, and 35% CGM were evaluated. Fingerling channel catfish (mean initial weight: 71 g/fish) were stocked into 24, 0.04‐ha ponds at a rate of 14,826 fish/ha. Fish were fed once daily to apparent satiation for a 167‐d growing season. No significant differences were observed in total amount of diet fed, diet consumption per fish, net yield, weight gain, feed conversion ratio, survival, fillet yield, and fillet protein, fat, and moisture concentrations among fish fed diets containing various levels of CGM. Carcass yield decreased linearly as dietary CGM levels increased. Depending on prices, CGM can be used interchangeably with corn gluten feed in channel catfish diets as replacements for corn, wheat middlings, and soybean meal to reduce feed cost.     

Low Protein Diets for Channel Catfish Ictalurus punctatus Raised in Earthen Ponds at High Density1

This study was conducted to evaluate the use of low protein diets for channel catfish Ictalurus punctatus raised in earthen ponds at high density. Fingerling channel catfish were stocked into 0.04-ha earthen ponds at a rate 24,700 fish/ha and fed experimental diets daily to satiation from April to October 1995. The five diets contained either 32, 28, 24, 20, or 16% crude protein with digestible energy to protein (DE:P) ratios ranging from 8.9 to 16.2 kcal/ g protein. Weight gain was not different among channel catfish fed diets containing 32, 28, or 24% crude protein. Fish fed diets containing 20% or 16% crude protein gained less weight than fish fed the diets containing 28% or 24% crude protein, but not statistically less than the fish fed the 32% crude protein diet. Feed consumption data followed similar trends as weight gain data. Feed conversion ratio increased linearly as dietary protein decreased, but was not significantly different (multiple range test) for fish fed diets containing either 32% or 28% crude protein. There were no differences in survival and hematocrit of fish fed the different diets. No differences (multiple range test) were observed in dressout percentages for fish fed the various diets, but dressout percentage tended to decrease linearly as dietary protein decreased. Visceral fat and fillet fat increased and fillet protein and moisture decreased linearly as dietary protein decreased. Results from this study indicated that dietary protein concentrations as low as 24% are adequate for maximum weight gain of pond-raised channel catfish fed daily to satiation. Fish fed dietary protein levels below 24% grew relatively well, particularly considering that dietary protein was reduced 40–50% below that typically used in commercial channel catfish feeds. However, dietary protein levels below 24% may increase fattiness to an unacceptable level presumably because of the high digestible energy to protein ratio.     

Substitution of Canola Meal for Soybean Meal in Diets for Channel Catfish Ictalurus punctatus

Abstract Canola meal was used in channel catfish Ictalurus punctatus diets at levels of 0, 15.4, 30.8, 46.2 and 61.6%, by progressively replacing (on an equal nitrogen basis) 0, 25, 50, 75, or 100% of solvent-extracted soybean meal in the control diet. The feeds were formulated to contain approximately 29% crude protein and 2,650 kcal of digestible energy/kg on an air-dry basis. Each diet was fed to juvenile channel catfish to satiation twice daily for 10 wk. Fish fed the diets containing the two lowest levels of canola meal (15.4 and 30.8%) had similar weight gains, feed intakes, feed utilization efficiencies, and percent survivals relative to the group fed the control diet. Weight gains and feed intakes declined significantly as the dietary levels of canola meal were increased to 46.2% or higher, probably because of reductions in diet palatability and some impairment of feed utilization due to the presence of increased levels of antinutritional factors, particularly glucosinolates. Whole body percentages for moisture and crude protein were unaffected by the dietary treatments. Body ash contents, however, were lowest for fish fed the control diets but were essentially the same for fish fed the other diets. Fish fed the diet containing 30.8% canola meal had lowest body fat content but this effect may not have been diet related. Values for red blood cell concentration, hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration were not affected by dietary canola meal level, but hematocrit was higher (although not always significant) for fish fed the control diet. The results of this study suggest that canola meal can comprise about 31% of the diet of channel catfish by replacing half of the amount of soybean meal used in the control diet without adversely affecting growth or any other aspect of performance.     

Supplemental Phosphorus in Practical Channel Catfish Diets1

Three experiments were conducted to evaluate the need for supplemental phosphorus in the diet of channel catfish Ictalurus punctatus as well as to compare dicalcium phosphate and defluorinated phosphate as sources of supplemental phosphorus. Fingerling channel catfish were stocked into 0.04-ha earthen ponds at a rate of 1,000 fish/pond (24,700ha). The fish were fed a feed typical of commercial catfish feeds containing 28% protein and 2.8 kcal digestible energy/g once daily to satiation during the growing season (April to October). Fish in experiment 2 were overwintered and fed at a rate of 1% body weight twice weekly when the water temperature exceeded 13 C. The basal diet used in experiments 1 and 2, which contained no supplemental phosphorus, had estimated available phosphorus concentrations of 0.26 and 0.20%, respectively. Dicalcium phosphate was added to provide available phosphorus concentrations of 0.34 and 0.41% for experiment 1, and 0.27 and 0.35% for experiment 2. Diets used in experiment 3 to compare dicalcium and defluorinated phosphates contained 0.40% available phosphorus. Data from experiments 1 and 2 indicated that a concentration of dietary phosphorus of about 0.27% was adequate for maximum weight gain and efficient conversion of feed by channel catfish. However, a concentration of about 0.35% available phosphorus was required for maximum bone mineralization in experiment 2. There were no differences in growth or bone mineralization between fish fed dicalcium or defluorinated phosphate. We conclude that the small increase in bone phosphorus (about 4%) is biologically insignificant, and suggest that 0.3% available phosphorus be adequate for channel catfish raised in earthen ponds. Also, either dicalcium or defluorinated phosphate can be used as a source of supplemental phosphorus in channel catfish diets. However, defluorinated phosphate may be desirable because of its low solubility in water.     

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.     

Multi-Locus DNA Fingerprinting of Channel Catfish Ictalurus punctatus

Abstract.— Similarities among multi-locus DNA fingerprints of five channel catfish Ictalurus punctatus strains and the ability to identify the strain of a fish based on its fingerprint pattern were investigated. Five restriction enzymes and 13 multi-locus DNA probes were screened to identify enzyme-probe combination useful for DNA fingerprinting channel catfish. Restriction enzymes Hinf I and Dpn II, in combination with probes (CAC)n, (CGC)n, (CTC)n, (ATCC)n, and (GATA)n, produced useful fingerprints (20–30 resolvable bands for each enzyme-probe combination). Thirty individuals (3 pools of 10 individuals each) from each of five channel catfish strains (albino, Mississippi normal, USDA-102, USDA-102 select, and USDA-103) were fingerprinted with all useful enzyme-probe combinations. Band sharing among samples was higher within strains than among strains and band sharing among strains was higher for strains whose breeding history indicated a high degree of relatedness. Individual fingerprints of 18 fish from each of the USDA-102 select and USDA-103 strains revealed no strain-specific bands, but several diagnostic bands (present at high frequencies in either USDA-102 select or USDA-103 strains and at a low frequencies in other strains) were identified. Band sharing at diagnostic bands was used to correctly identify fish as USDA-102 select or USDA-103 strains with 82% accuracy from fingerprints of 17 USDA-102 select strain fish, 18 USDA-103 strain fish, and 38 fish collected from three commercial farms.     

Behavioral Interactions in Juvenile Channel Catfish,Ictalurus punctatus

Behavioral interactions among juvenile channel catfish, "Ictalurus punctatus," were observed, and fixed action patterns were described and anlyzed. Dominant fish engaged regularly in aggressive activities and never in submissive activities, whereas subordinate fish were observed in submissive activities on a regular basis and rarely in those that were aggressive. Activity levels were significantly higher in dominant fish; however, there was no difference in activity levels between pairs of equal and unequal size fish. A factor analysis indicated that there were three general categoris of behavior in juvenile channel catfish. In addition, two behaviors (which appeared to be displacement activities) were functioning in agnostic encounters. Plasma cortisol concentrations measured in sigle fish and pairs of fish in aquaria and individuals from a holding tank indicated that the least amount of stress occurred in fish that were not interacting with any other individuals. Cortisol levels, however, were lower that those associated with stress levels in fish from other studies.     

Evaluation of Cuphea Meal as an Ingredient Replacement in Channel Catfish,Ictalurus punctatus,Diets

ABSTRACT

Cuphea meal is a new, alternative feedstuff that has potential as a sustainable, economical replacement for wheat, rice, and corn ingredients in channel catfish, Ictalurus punctatus, diets. Channel catfish fingerlings were fed a control diet containing wheat or two experimental diets containing 7.5% cuphea meal, or 12.5% cuphea meal for eight weeks to determine if cuphea meal could replace wheat products in catfish diets. Mean (±SE) weight gains were 317.8 ± 28.8 g, 407.0 ± 36.9 g, and 372.8 ± 29.8 g for fish fed the control diet, the 7.5% cuphea meal diet, and the 15% cuphea meal diet, respectively, and there were no significant differences (P < 0.05) among treatments. Mean (±SE) whole-body protein of fish fed the cuphea diets (13.3 ± 0.66 and 14.5 ± 0.21%) was significantly (P < 0.05) higher than that of fish fed the wheat diet (12.7 ± 0.44%). Cuphea meal enhanced body composition of juvenile channel catfish without affecting growth or survival. Therefore, cuphea meal is a promising candidate for replacement of wheat bran at the levels tested.     

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.     

Application of Compensatory Growth to Enhance Production in Channel Catfish Ictalurus punctatus

Four treatment groups that received repeating cycles of fixed feed deprivation for either 0, 1, 2, or 3 d (control, treatment 1, treatment 2, and treatment 3, respectively), followed by periods of refeeding with a 36% protein commercial catfish feed once daily as long as the active phase of compensatory growth (CG) persisted, were assessed in flow-through aquaria. No-feed periods elicited the CG state and were immediately followed by days of ad libatum refeeding. At the end of 10 wk, average growth rate (AGR) of fish was higher ( P < 0.05) than the control by 40%, 180%, and 191% for treatment 1, treatment 2, and treatment 3, respectively. The average weight of fish in treatment 3 was heavier ( P < 0.05) than the average control group at the end of the study period. Mean daily feed consumption was 3.91%, 5.03%, 5.36%, and 5.98% for control, treatment 1, treatment 2, and treatment 3, respectively. Mean feed consumption per fish per day was 24%, 71.3%, and 70.7% higher than the control in treatment 1, treatment 2, and treatment 3, respectively. Restricted feeding is one of the effective methods to contain ESC-related losses in commercial channel catfish fingerling operations. The mean cumulative survival of treatment groups registered higher ( P < 0.05) survival to Edwardsiella ictaluri infection compared to the daily fed control fish. Results from this study show that compensatory growth response triggered by periodic non-feeding days can improve growth rate, feed consumption, and improved survival to ESC infections in channel catfish fingerlings.     

Net Absorption of Dietary Phosphorus from Various Inorganic Sources and Effect of Fungal Phytase on Net Absorption of Plant Phosphorus by Channel Catfish Ictalurus punctatus

Year-2 channel catfish (average weight 765 g) were fed a commercial-type, all-plant diet containing supplemental phosphorus (0.40%) from one of various sources, or fungal phytase (1,000 and 3,000 units), in 1-m³ circular raceways for 21 d at a temperature of 28–30 C. Subsequently, net absorption of phosphorus from the diets was determined by the chromic oxide indicator method in which feces were collected from the rectum. Net absorption of the supplemental phosphorus was corrected for the absorbed residual phosphorus in the basal diet. Net absorption coefficients for monosodium phosphate, monoammonium phosphate, finely ground defluorinated rock phosphate and monocalcium phosphate were 88.6, 85.4, 81.7, and 81.2%, respectively, and were not significantly different. Net absorption coefficient for dicalcium phosphate was significantly lower, 74.8%, but was significantly higher than those for coarsely ground defluorinated rock phosphate and tricalcium phosphate, which were 55.1 and 54.8%, respectively. These data are in general agreement with relative bioavailability values based on growth response for channel catfish determined in other research, and should be appropriate for determining available phosphorus allowances in commercial feeds and establishing phosphorus budgets in aquaculture feeding operations. The net absorption of phosphorus from the all-plant basal diet was 31.2% and increased significantly to 55.1 and 62.5% with the addition of 1,000 and 3,000 units of fungal phytase, respectively.     

Channel Catfish,Ictalurus punctatus,Immunity to Saprolegnia sp.

ABSTRACT

The Japanese flounder, Paralichthys olivaceus, is one of the most common finfish cultured in Japan and Korea. Despite the relatively high production of fingerlings, some problems remain, mainly related to the larval feeding and cost of maintaining microalgae and rotifers. In order to determine the effects of different diets on the Japanese flounder larval growth and survival, a series of experiments was carried out related to the size and nutritional value of different live feeds. The larvae culture conditions were at 10 or 20 larvae/L in 50 to 2,000 L tanks, with aeration and with or without “green water,” and a temperature range of 18.5 to 22.5°C. The live foods used were microalgae (Chlorella ellipsoidea and Nannochloris oculata), baker's yeast, experimental n-yeasts, oyster trochophore larvae, three strains of rotifer Brachionus plicatilis (L-type, S-type and U-type) and Artemia nauplii. Variations were detected in size, dry weight, and chemical composition of the three strains of rotifers used. The maximum number of rotifers ingested by flounder larvae increased steadily from 7 individuals, at first feeding (3.13 mm), to 42 individuals at 5.25 mm of total length (6 days after first feeding). There was a relationship between larval total length and size of the rotifers ingested. The effect of rotifer size on larval growth and survival appeared to be limited to the first two days of feeding. Of the diets tested in the growth and survival of larval flounder during 14 days after hatching, rotifers fed on C. ellipsoidea and raised in green-water gave the best results. Rotifers cultured on enriched N. oculata and n-yeasts did not support larval growth and caused higher mortalities. The n-yeasts used as rotifer enrichment appeared to satisfy, partially, the nutritional requirement of 7-day-old flounder larvae, as did n-yeast squid wintering oil the requirements of 14-day-old larvae. From 7-9-days after hatching and throughout the second 14-day period, rotifers and Artemia cultured on N. oculata improved the survival of flounder compared with those fed on rotifers cultured on C. ellipsoidea. Moreover, the larval growth did not vary significantly between both microalgae-rotifer feedings. No clear relation was found between total protein, lipid, amino acids and fatty acids of live feeds with the growth and survival of flounder larvae, although the total lipid was higher in C. ellipsoidea than in N. oculata. The Artemia nauplii San Francisco strain appeared to be more suitable for the growth and survival of flounder larvae, than the Utah strain. The nutritional value of Artemia nauplii (Utah strain) for flounder larvae remained unchanged despite the use of either microalgae as nauplii enrichment.     

Environmental Assessment of Channel Catfish Ictalurus punctatus Farming in Alabama

An environmental assessment was made of Alabama channel catfish Ictalurus punctatus farming which is concentrated in the west‐central region of the state. There are about 10,000 ha of production ponds with 10.7% of the area for fry and fingerlings and 89.3% for food fish. Food fish production was about 40,800 tons in 1997. Watershed ponds filled by rainfall and runoff make up 76% of total pond area. Water levels in many of these ponds are maintained in dry weather with well water. The other ponds are embankment ponds supplied by well water. Harvest is primarily by seine‐through procedures and ponds are not drained frequently. The main points related to Alabama catfish farming and environment issues are as follows: 1) catfish farming in Alabama is conservative of water, and excluding storm overflow, about two pond volumes are intentionally discharged from each pond in 15 yr; 2) overflow from ponds following rains occurs mostly in winter and early spring when pond water quality is good and stream discharge volume is high; 3) total suspended solids concentrations in pond effluents were high, and the main sources of total suspended solids were erosion of embankments, pond bottoms, and discharge ditches; 4) concentrations of nitrogen and phosphorus in effluents were not high, but annual effluent loads of these two nutrients were greater than for typical row crops in Alabama; 5) ground water use by the industry is about 86,000 m³/d, but seepage from ponds returns water to aquifers; 6) there is little use of medicated feeds; 7) copper sulfate is used to control blue‐green algae and off‐flavor in ponds, but copper is rapidly lost from pond water; 8) although sodium chloride is applied to ponds to control nitrite toxicity, stream or ground water salinization has not resulted from this practice; 9) fertilizers are applied two or three times annually to fry and fingerling ponds and occasionally to grow‐out ponds; 10) hydrated lime is applied occasionally at 50 to 100 kg/ha but this does not cause high pH in pond waters or effluents; 11) accumulated sediment removed from pond bottoms is used to repair embankments and not discarded outside ponds; 12) sampling above and below catfish pond outfalls on eight streams revealed few differences in stream water quality; 13) electricity used for pumping water and mechanical aeration is only 0.90 kW h/kg of production; 14) each metric ton of fish meal used in feeds yields about 10 tons of dressed catfish. Reduction in effluent volume through water reuse and effluent treatment in settling basins or wetlands does not appear feasible on most farms. However, some management practices are recommended for reducing the volume and improving the quality of channel catfish pond effluents.     

Biochemical Oxygen Demand in Channel Catfish Ictalurus punctatus Pond Waters

A study of the biochemical oxygen demand (BOD) of waters from ten channel catfish ponds at Auburn, Alabama, revealed that the 5-d BOD (BOD₅) seldom exceeded 8 mg/L and that the ultimate BOD (BOD_u) was usually less than 30 mg/L. Water samples from catfish ponds usually needed to be diluted only 2 or 3 times to permit BOD₅ measurements, and nitrification occurred even during a 5-d incubation period. Catfish pond waters were not extremely high in ammonia nitrogen concentration, and ammonia nitrogen introduced in the ammonium chloride-enriched dilution water caused an appreciable increase in BOD of some samples. Plankton respiration is a major component of carbonaceous BOD (CBOD) in catfish pond waters. Thus, the BOD is not expressed as rapidly during 5-d incubations as in typical waste-water. The ultimate BOD (BOD_u) would be a good measurement of oxygen demand for catfish pond effluents, but it is difficult to measure. Data from this study suggest that BOD_u can be estimated from BOD₅, but the correlation is not strong ( R ²= 0.62). An alternative is to develop a short-term BOD measurement specifically for effluents from channel catfish and other aquaculture ponds. This study suggests that a 10-d BOD conducted without nitrification inhibition or addition of ammonia nitrogen in dilution water might be a better alternative to standard BOD₅ or BOD_u measurements normally used in wastewater evaluation.     

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 Channel Catfish,Ictalurus punctatus,and Blue Catfish,Ictalurus furcatus,Fed Diets Containing Various Levels of Protein in Production Ponds

A comparative study was conducted on growth and protein requirements of channel catfish, Ictalurus punctatus, and blue catfish, Ictalurus furcatus. Four diets containing 24, 28, 32, or 36% protein were fed to both channel (initial weight 6.9 g/fish) and blue (6.6 g/fish) catfish for two growing seasons. There were significant interactions between dietary protein and fish species for weight gain and feed conversion ratio (FCR). No significant differences were observed in weight gain of channel catfish fed various protein diets, whereas higher protein diets (32 and 36%) resulted in better weight gain in blue catfish than lower protein diets (24 and 28%). No consistent differences were observed in the FCR of channel catfish fed various levels of dietary protein, whereas significantly higher FCRs were noted in blue catfish fed the 24 and 28% protein diets compared with fish fed 32 and 36% protein diets. Regardless of dietary protein levels, blue catfish had higher carcass, nugget, and total meat yield, and higher fillet moisture and protein, but lower fillet yield and fillet fat. Regardless of fish species, fish fed the 36% protein diet had higher carcass, fillet, and total meat yield than fish fed the 28 and 32% protein diets, which in turn had higher yields than fish fed the 24% protein diet. It appears that blue catfish can be successfully cultured by feeding a 32% protein diet.     

Wildlife-Caused Losses for Producers of Channel Catfish Ictalurus punctatus in 1996

The National Agricultural Statistics Service surveyed by telephone and mail in January and February 1997 all known producers of channel catfish letalurus punctatus to acquire current information about wildlife-caused losses in calendar year 1996. Many producers tried to prevent wildlife-caused losses of their catfish by shooting (57%), vehicle patrol (55%), or frightening (36%), at an estimated cost of >$5 million. Yet, 69% of catfish producers cited some wildlife-caused losses. Birds were most frequently cited as a cause of losses, and double-crested cormorants Phalacrocorax auritus was the species cited most frequently (53%). The next most frequently cited birds were herons Ardea spp. (48%), egrets Egretta spp . (16%), and pelicans Pelecanus spp. (8%). Muskrats Ondatra zibethicus were cited by 10% of producers, primarily for damaging dikes and roads. The main problems caused by wildlife were feeding on catfish (67%), injuring catfish (40%) or disturbing feeding patterns of the catfish (23%). The total estimated cost of losses was $12 million. Overall, wildlife damage and damage prevention may have cost catfish producers > $17 million, about 4% of the total $425 million of catfish sales in 1996. Of the 44% of all catfish producers who were familiar with Wildlife Services (WS), 51% had ever contacted WS for assistance, 55% used methods suggested by WS to reduce their losses, and 40% received direct assistance from WS in 1996. Mississippi producers, who most frequently received direct assistance from WS, had proportionately lower wildlife-caused losses.     

Evaluation of Three Strains of Channel Catfish Ictalurus punctatus Fed Diets Containing Three Concentrations of Protein and Digestible Energy1

Abstract A 3 × 3 factorial experiment was conducted using three strains of channel catfish Ictalurus punctatus, USDA102, USDA103, and Mississippi normal (MN), and three concentrations of dietary protein. Three practical diets were formulated to contain 25, 35, or 45% crude protein with digestible energy/protein ratio of 10.0, 8.1, or 6.8 Kcal/g, respectively. Juvenile channel catfish (mean initial weight: 15.1 g/fish) were fed the experimental diets twice daily to approximate satiation for 8 wk. Regardless of dietary protein concentration, the USDA 103 strain consumed more feed, gained more weight, and converted feed more efficiently than other two strains. The MN strain consumed less feed and gained less weight than the other strains. Regardless of the strain of channel catfish, differences in weight gain, feed consumption, and feed conversion ratio were observed among fish fed diets containing various levels of protein with the 35% protein diet being the best. Neither dietary protein concentration nor strain had significant effect on fillet protein level. Data pooled by fish strain showed that fish of MN strain had lower fillet fat and higher moisture than fish of other two strains. Data pooled by dietary protein showed that fish fed the 45% protein diet had a lower level of fillet fat than fish fed the 35% protein diet, but this did not appear to be a strain effect, rather it was a result of decreased feed consumption. Results from this study clearly demonstrate that per formance of the USDA103 strain of channel catfish was superior to other strains tested. The growth characteristics of the USDA103 strain of channel catfish make the strain a promising candidate for commercialization. However, data are needed on performance of the strain from fingerling to marketable size under conditions similar to those used for the commercial culture of channel catfish prior to their release to the catfish industry.