Impact of Great Blue Heron Depredations on Channel Catfish Farms

With the growth of channel caffish Ictalurus punetatus production in the Delta Region of Mississippi over the last 30 years have come concurrent depredation problems caused by great blue herons Ardea herodias . Biomass in stomachs from herons collected at catfish farms averaged 41% catfish, 38% sunfish Lepomis sp ., 17% shad Dorosoma cepedianum , and 4% gambusia Gambusia sp.; whereas observations of herons foraging indicated that 45% of the prey taken were gambusia. Our observational data indicate that herons take an average of 12 10-cm catfish fingerlings daily. The diurnal density of foraging herons on catfish ponds averaged 0.17 herons/ha in 1990, which means that the average 127-ha farm supports approximately 22 herons. Nocturnal foraging, especially on dark nights, appears to be minimal. If our data are approximately correct, the average catfish farm could be losing $30/ha per yr to herons, assuming that this catfish fingerling mortality can be attributed solely to heron depredation.     

Foraging Behavior and Monetary Impact of Wading Birds at Arkansas Baitfish Farms

Abstract— We conducted foraging observations, food habits studies, and producer surveys to determine the foraging behavior and monetary impact of great blue herons Ardea herodas , great egrets A. alba , and little blue herons Egrerra caerulea foraging at Arkansas baiffish farms. Although great egrets captured most baitfish/minute, captures/strike were nearly identical among the three wading bird species. American gizzard shad Dorosoma cepedianum , goldfish Carassius auratus , and giant water bugs Hemiptera: Belostomatidae were collected from the gastro-intestinal tract of great blue herons. Only golden shiners Noremgonus crysoleucas and goldfish were found in great egrets. We found dragonflies Odonata , golden shiners, green sunfish Lepomis cyanellus , and water bugs in little blue herons. In contrast to other birds collected, snowy egrets E. thula were found to contain mosquito fish Gambusia affinis . Among 2,742 teleost otoliths recovered from collected great blue herons, great egrets, and little blue herons, most otoliths belonged to the Cyprinidae family (including the baiffishes). Surveyed farm managers use various auditory and visual stimuli to disperse fish-eating birds from their farms. Surveyed baitfish farmers suggested that the average cost of their annual bird harassment program was $11,580 at relatively small farms (< 202 ha) and $104,560 at relatively large × 202 ha) baitfish aquaculture facilities. We estimated the replacement cost of baitfish consumed by wading buds based upon their daily food requirements, the food habits of herons and egrets at baiffish farms, the hypothetical abundance of wading birds at a particular baitfish farm (relative to survey results), the duration of herons and egrets reported by farm managers, and current baitfish market values.     

Evaluation of a Methyl Anthranilate-Based Bird Repellent: Toxicity to Channel Catfish Ictalurus punctatus and Effect on Great Blue Heron Ardea herodias Feeding Behavior

Abstract— We evaluated the methyl anthranilate-based bird repellent, ReJeX-iT TP-40™ (TP-40), for 1) its toxicity to channel catfish fingerlings (catfish), Ictalurus punctatus; 2) its effect on great blue heron (heron), Ardea herodias feeding behavior; 3) its efficacy in reducing heron predation on catfish; and 4) its effects on catfish growth. TP-40 effectively maintained MA concentrations near the water's surface and below toxic levels for catfish in the water column. Water samples collected from 0.03 and 0.35 m below the surface of catfish rearing tanks (6,664 L) treated at application rates up to the equivalent of 200 kg/ha contained less than 5 ppm active ingredient, which is less than the no observable effect limit for catfish fry. No treatment-related mortality of catfish was observed. Handling times of catfish fingerlings captured by herons from tubs treated with TP-40 initially increased at application rates of 19.6 kgha or greater but decreased as a function of the number of catfish captured. Under simulated aquaculture conditions, TP-40 did not affect the number of catfish eaten by herons from ponds treated at surface application rates of 0, 2, 22, and 220 kglha. TP-40 had no affect on the time herons spent handling live or dead catfish. Ponds treated with TP-40 at 220 kgha had a 46% increase in visibility (secchi disk method) and a 58% reduction in total suspended solids, suggesting the formulation was phytotoxic. TP-40 did not affect fish growth. Analysis of individual behavior showed that herons may have habituated or become indifferent to the effects of the repellent after repeated exposure. Under the conditions of the study, herons did not maintain their body weight unless catfish were made available by disease or supplemental feeding, suggesting that herons may be inefficient at capturing healthy catfish. Surface applications of TP-40 at 20 to 220 kg/ha were not effective in limiting predation by herons.     

Recovery and Viability of Edwardsiella ictaluri from Great Blue Herons Ardea herodias Fed E. ictaluri-Infected Channel Catfish Ictalurus punctatus Fingerlings

Feeding activities of great blue herons Ardea herodias in catfish ponds during outbreaks of enteric septicemia of catfish have been implicated as a mechanism for the transmission of the disease from infected to uninfected ponds. Although Edwardsiella ictaluri , the causative agent, has been identified in gastrointestinal tracts of great blue herons, the role of these birds as a vector of E. ictaluri is not well documented. The potential of these birds to contaminate catfish ponds with E. ictaluri was investigated by feeding captive herons over a 4-d period with catfish fingerlings injected intraperitoneally with live E. ictaluri . Daily fecal samples, throat and rectal swabs, and feather samples were collected, cultured and examined for E. ictaluri using both a selective media and a monoclonal indirect fluorescent antibody test specific for E. ictaluri . Gastrointestinal tracts sampled at the conclusion of the feeding trial were similarly examined. While E. ictaluri was detected using the indirect fluorescent antibody test, no viable E. ictaluri was cultured from either feces, gastrointestinal tracts or feathers. Growth of E. ictaluri was not observed at 40 C, the rectal temperature observed in captive great blue herons. Prior incubation at 40 C suppressed the growth of E. ictaluri at 24 C, an optimal temperature for growth of this bacterium. These results indicate that great blue herons appear to play little or no role in the transmission of E. ictaluri among catfish ponds.     

Principal economic effects of cormorant predation on catfish farms

Substantial economic losses of farmed catfish to fish‐eating birds such as the double‐crested cormorant, Phalacrocorax auritus, continue to be reported on U.S. catfish farms. An economic analysis was conducted of the on‐farm effects of both the increased expenditures to scare fish‐eating birds from catfish farms and of the value of the catfish that were consumed by cormorants. A survey was conducted of U.S. catfish farmers in the Delta region of Mississippi and Arkansas, to obtain farm‐level data on expenditures to scare birds. Estimations of the lost revenue from catfish consumed by cormorants were developed from a concurrent study on cormorant distribution, abundance, and diet in the region. The economic effects of bird predation in terms of both fish consumption and management costs were evaluated across three farm sizes and nine catfish production practices. Catfish farmers spent on average $704/ha ± $394/ha to scare birds, making bird‐scaring costs one of the top five costs of raising catfish. The greatest cost components of scaring birds were manpower (39% of all bird‐scaring costs) and the variable and fixed costs of trucks used to scare birds (34% of all bird‐scaring costs). Losses were greater on hybrid than channel catfish fingerling ponds. Industry‐wide, the value of catfish losses averaged $47.2 million (range of $25.8–$65.4 million). Total direct economic effects (including both the increased costs to scare birds and the revenue lost from fish consumed by cormorants despite bird‐scaring attempts) averaged $64.7 million (ranging from $33.5 to $92.6 million). Profitability improved by 4% to 23% across the farm size/production strategies analyzed upon removal of the economic effects from bird predation, with greater effects occurring on smaller‐scale farms. One‐third of the farm size and production scenarios analyzed changed from being unprofitable to showing a profit in the absence of such negative economic effects associated with bird depredation. Overall, the combined effects of increased farm expenditures to scare birds from farms and the value of the catfish lost to predation by cormorants caused substantial negative economic effects on catfish farms.     

Grey heron, Ardea cinerea L., predation at cage fish farms in Argyll, western Scotland

Abstract. The aims of the present study were to determine the number and age structure of grey herons, Ardea cinerea L., visiting a large freshwater cage trout farm in a study area in Argyll, western Scotland and to quantify heron predation at the site. Heron abundance was assessed on sea loch shores, running and standing freshwater bodies and at the trout farm between September 1985 and August 1987. Herons visited the farm almost exclusively at night or during twilight periods and, as a consequence, were seen more often by farm staff in winter than in summer. Herons selected cages containing small trout (<300g) and removed them from cages by standing on the top nets and fishing through the mesh. Stock losses were of two kinds; trout were either eaten directly or were dropped by herons during manipulation, when characteristic wounds increased susceptibility to disease or made the fish unmarketable. Adult herons were more successful at feeding than first-years and although younger birds spent more time feeding their intake rates remained lower than those of adults in terms of their total time at the farm. Within a cage, smaller fish aggregated closer to the surface than larger ones and so were more vulnerable to heron predation. In many cases, a high proportion of the fish attacked by herons were blind and/or in poor condition. By recording only wounded fish, farm staff considerably underestimated their losses to herons. Nevertheless, attacks sometimes appeared serious to farmers. However, such losses were small compared with other forms of fish mortality and loss.     

Quantitative estimation of the predation of marine ranched striped jack <Emphasis Type="Italic">Pseudocaranx dentex</Emphasis> by herons

The Goto station of the Japan Sea-Farming Association conducted marine ranching experiments with striped jack Pseudocaranx dentex from 1988 to 1999 in the Goto Islands, Nagasaki, Japan. Marine ranching is a stocking method where released fish are fed for some period after release in order to decrease initial mortality from starvation. Ranched fish were fed for 0, 90, and 15 days after stocking in 1997, 1998, and 1999, respectively. During the experiment, herons (grey heron Ardea cinerea, black-crowned night heron Nycticorax nycticorax, and great egret Egretta alba) were often observed preying on released fish in the ranching area. The present study estimated the number of fish preyed upon by herons during observation periods in 1997, 1998, and 1999 from the number of herons that flew into the ranching area and the predation rate on ranched fish by herons. The former was counted during sightings. The latter was estimated from the sighting observations and heron regurgitations. The number of herons that flew into the ranching area increased with the feeding period. The numbers of fish lost to predation by herons in 1997, 1998, and 1999 were estimated to be 0, 5,741, and 829, respectively.     

Temporary Sequestration of Fingerling Channel Catfish in Cages as a Means to Improve Production of Multiple-Crop Ponds

Abstract

Two studies were conducted to determine if temporary sequestration of fingerling channel catfish, Ictalurus punctatus, in cages improves production of multiple-crop ponds. In the first study, 0.04-ha ponds were stocked with 295 large (mean weight = 566 g) and 780 fingerling (mean weight = 21 g) catfish. Fingerlings were stocked into cages or open ponds. At 120 days after stocking, fish in cages were released. After an additional 40 days, ponds were clean-harvested to remove large (>500 g) and small (<500 g) fish. In the second study, ponds (0.08-ha) were stocked with 750 large (mean weight = 46 g) and 750 small (mean weight = 20 g) fingerling catfish. Small fingerlings were stocked into cages or open ponds. At 60 days after stocking, fish in cages were released. Market-ready fish were selectively harvested at five and nine months after stocking. Results from the first study indicated that individual weight, weight gain, and yield of both size classes of fish raised in sequestered ponds were significantly greater (P< 0.05) than that of fish raised in open ponds. In addition, total weight gain and yield of fish in sequestered ponds was significantly greater (P< 0.05) than those in non-sequestered ponds. Results from the second study indicated that a significantly greater (P< 0.05) number of market-ready fish were harvested from sequestered ponds than from non-sequestered ponds. Mean yield of sequestered ponds was 31% greater than that of non-sequestered ponds; however, differences were not significant (P> 0.05). Amount of feed fed to fish raised in sequestered ponds was significantly greater (P< 0.05) than amount of feed fed to fish raised in non-sequestered ponds in both studies. It is unclear which factor or factors were responsible for the enhanced production of sequestered ponds; however, temporary sequestration may reduce agonistic behavior and competition for feed between fish size groups.     

Evaluation of a Confinement System for Growout of Channel Catfish Ictalurus punctatus

Rising costs of inputs have created a need to improve catfish production efficiencies. An inexpensive confinement system was evaluated for channel catfish Ictalurus punctatus foodfish production. Barriers were constructed in five 0.1-ha earthen ponds to partition ponds into 1/3 and 2/3 sections. Large fingerling (136 g) catfish were stocked at 11,115 fish/ha in the smaller 1/3 section (shallow end) of the confinement ponds or in open ponds (control). Seining efficiency was significantly greater for the confinement system. Yield and daily growth of food fish were significantly lower and feed conversion ratio higher in the confinement system compared to open ponds. Partial budget analysis showed a net loss of –$313/ha. Additional work is needed to develop inexpensive production systems to capture efficiencies of confinement without decreasing production.     

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.     

Impact of Double-Crested Cormorant Depredations on Channel Catfish Farms

Resurgent wintering populations of double-crested cormorants in the past 10 years have caused serious depredation problems for commercial channel catfish ( Ictalurus punctarus ) growers in Mississippi. Catch rates of catfish by cormorants were found to average 5 catfish per cormorant-hour. Catfish taken averaged 12 cm in length. However, cormorants took fingerling catfish at rates as high as 28 per cormorant-hour. The average number of cormorants found feeding on a single pond in this study was 30.5. If this number (but not necessarily the same individuals) fed all day in an 8 ha pond stocked at 51,000 fishlha, the fish population would be halved in 30 days. Further, using this example, the cost of harassment patrols on a 200 ha catfish farm complex over a 5 month period would be exceeded in 22 days by the losses in this one pond. Wild gizzard shad ( Dorosoma cepedianum ) occurred in some ponds, and seem to be preferred by cormorants over caffish.     

Growth, Yield, Dressout, and Net Returns of Bighead Carp Hypophthalmichthys nobilis Stocked at Three Densities in Catfish Ictalurus punctatus Ponds

Abstract— Alternative fish species that can be cultured together with catfish Ictalurus punctatus provide an opportunity to diversify caffish farms. A 2-yr study was conducted in 0.10-ha earthen ponds to evaluate the effect of bighead carp (BHC) stocking density on growth, yield, dressout yield, and net returns. Initially, bighead carp (average weight of 22 g) were stocked at rates of 380, 750, or 1,130 fishha in ponds with catfish. Caffish were cultured under commercial conditions by stocking caffish at a density of 12,500/ha, aerating nightly and feeding at an average rate of 82 kgha per d. Stocking rates for 2-yr-old fish were reduced to 77, 260, and 435/ha in the second growing season. There were no significant differences among treatments ( P > 0.05) in summer growth of bighead carp in either year. Bighead carp stocked at 1,130 fishha had significantly higher yields than those stocked at 380/ha, but did not reach minimum market size of 2.2 kg during the first year ( P > 0.05). There were no significant differences ( P > 0.05) in caffish growth, yield, survival, or feed conversion ratios due to the bighead carp stocking densities. Partial budget analysis indicated that net benefits were positive for all three treatments over a range of prevailing prices of bighead carp. Bighead carp production in catfish ponds is economically feasible over a wide range of prices. Given the market risk of producing smaller fish at the higher density, the medium density is the preferred stocking density of fingerling bighead carp in catfish ponds.     

Threadfin Shad Dorosoma petenense Effects on Water Quality, Phytoplankton, and Channel Catfish Production in Ponds

Threadfin shad Dorosoma petenense are often stocked into commercial catfish ponds for biological control of algae. It is thought that the fish will alter the phytoplankton community, improve water quality, and enhance channel catfish production. Co-stocking of shad and catfish is a common practice, although there is limited information regarding the effects of threadfin shad on pond dynamics and catfish production. To evaluate the influence of shad in catfish ponds, this study was conducted in ten 0.04-ha experimental earthen ponds near Auburn, Alabama. All ponds were stocked in April with 600 fingerling channel catfish Ictal-urus punctatus (13,200/ha) with a mean length of 10.4 cm (4.1 in). Additionally, five of these ponds were randomly chosen and stocked with 70 adult threadfin shad (1,750/ha) weighing a total of 3.3 kg (16.5 kg/ha). At harvest in November, an average of 1,284 threadfin shad (32,100/ha), weighing a total of 55 kg (1,375 kg/ha) were collected from each shad pond. Water quality was improved with the addition of threadfin shad to channel catfish ponds. Mean total ammonia-nitrogen was significantly lower and less variable in the shad treatment. Observed mean nitrite concentrations, though not significant, were lower in the shad treatment. The phytoplankton community of the shad treatment had significantly higher density, more taxa, and smaller organisms. Pond water in the shad treatment had higher projected early morning dissolved oxygen levels requiring less aeration. Channel catfish had significantly higher survival in the shad treatment, furthermore, though not statistically significant, observed mean fish production was higher and feed conversion ratio was lower than in the no-shad treatment.     

Economic assessment of commercial-scale Edwardsiella ictaluri vaccine trials in U.S. catfish industry

Abstract

Enteric Septicemia of Catfish (ESC) is a ruinous bacterial disease affecting the U.S. catfish industry. Previous attempts to develop ESC vaccines have failed to achieve industry acceptance, largely attributed to difficulties in delivering the vaccine to immunocompetent fish. Recently, a live attenuated ESC vaccine has been developed, coupled with a mechanized platform designed to accurately deliver measured doses of vaccine with feed. This delivery scheme for vaccine-feed admixture has shown tremendous promise under controlled research settings. This study evaluated the economic effects of on-going commercial-vaccination trials on catfish fingerling operations in Mississippi. Commercial-vaccination trials for both channel and hybrid catfish demonstrated significant improvement in survival, growth, feed consumption, feed conversion and gross yield. At a realistic vaccination cost of $750/ha, the net economic benefits to channel and hybrid catfish fingerling-production phases were $3199 and $6145/ha, respectively. Whole-farm models showed additional profit ranging from $71,758 to $133,887/400-ha on farms that integrate fingerling production to their production strategies due to appropriation of more of the otherwise incumbent fingerling production acreage into foodfish production. Commercial adoption of the oral-vaccination platform would greatly enhance profitability while laying the foundation for development and delivery of polyvalent vaccines against other catfish diseases.     

Overwintering Paddlefish in Monoculture and in Polyculture with Channel Catfish and Rainbow Trout

Paddlefish, "Polydon spathula," overwintered in monoculture and in polyculture with fingerling channel catfish, "Ictalurus punctatus," or with rainbow trout, "Oncorhynchus mykiss," were examined for growth and compatibility in nine 0.04-ha ponds. Paddlefish in polyculture had significantly greater (P ≤ 0.05) individual weight gains than those in monoculture. Feed in polyculture treatments probably served as a fertilizer, promoting zooplankton production for paddlefish consumption and growth. Paddlefish in polyculture with fingerling channel catfish had significantly greater (P < 0.05) individual weight gains than paddlefish polycultured with rainbow trout, although there was less feed input with channel catfish than with rainbow trout. Bloody and frayed fins on paddlefish stocked with rainbow trout suggested fin nipping by rainbow trout which may have interfered with paddlefish feeding and growth. Paddlefish overwintered in polyculture with fingerling channel catfish demonstrated increased weight gains and good species compatibility.     

Effects of Feeding Diets with and without Fish Meal on Production of Channel Catfish,Ictalurus punctatus,Stocked at Varying Densities

ABSTRACT

Animal protein, generally fish meal, has traditionally been used in the diet of channel catfish. However, our previous research indicates that animal protein is not needed for growing stocker-size catfish to food fish when the fish are stocked at densities typical of those used in commercial catfish culture. Whether this holds when fish are stocked at high densities is not known; thus, we conducted an experiment to evaluate the effect of feeding diets with and without fish meal to channel catfish stocked in earthen ponds at different densities. Two 32% protein-practical diets containing 0% or 6% menhaden fish meal 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 g/fish were stocked into 30 0.04-ha ponds. Five ponds were randomly allotted for each fish meal level?×?stocking density combination. Fish were fed once daily to satiation for two growing seasons. There was a significant interaction between stocking density and fish meal for net production; net production increased in fish fed a diet containing fish meal compared with those fed an all-plant diet at the highest stocking density, but not at the two lower stocking densities. Net production of fish fed diets with and without fish meal increased as stocking density increased. Viewing the main effect means, weight gain decreased and feed conversion ratio increased for fish stocked at the two highest densities, and survival was significantly lower at the highest stocking density. Visceral fat decreased in fish at the two highest stocking densities. Body composition data were largely unaffected by experimental treatment except for a reduction in percentage filet fat in fish at the highest stocking density, and fish that were fed diets containing fish meal had a lower percentage fillet protein and a higher percentage fillet fat. It appears that at stocking densities two to three times higher than generally used, animal protein (fish meal) may be beneficial in the diet of channel catfish. In regard to stocking densities, high stocking results in higher overall production, but the average fish size decreased as stocking density increased.     

Transmission of some fish pathogenic viruses by the heron, Ardea cinerea

Abstract. Various possibilities of transmitting fish pathogenic VHS, SVC and IPN viruses by the heron, Ardea cinerea , were investigated. Shedding of IPN virus in the faeces could be demonstrated for a period of 7 days when about 1 g of IPN virus-infected trout fry was fed to the birds once only, whereas feeding larger quantities of infected fish on 5 consecutive days resulted in virus excretion for a further 5 days only. Infectious IPN virus could not be isolated from samples of blood and virus specific neutralizing antibodies could not be demonstrated in serum samples. A waterborne infection of trout fry was established by adding very small (0·2 g) quantities of faeces from herons fed IPN virus-contaminated fish to 20 1 water. Infectious SVC and VHS virus was also re-isolated from samples of food which were regurgitated by the herons at different times up to 120 min after feeding of contaminated fish. It was concluded that herons are able to act as mechanical vectors for IPN, VHS and SVC viruses and therefore, may be a potential source of infection and spread of the diseases.     

Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and ponds

Growth and survival of hatchery‐bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m^?3 in tanks and 114, 228 and 457 fry m^?3 in ponds. Fish were fed a formulated diet throughout the 28‐day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day^?1, than those in cages suspended in tanks (SGR range 9–11.3% day^?1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m^?3 were similar to each other but were significantly lower than those of fish held at 114 m^?3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m^?3 in tanks and at 114 m^?3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow‐out culture can still be attained at stocking densities of 457 m^?3 in nursery pond and 571 m^?3 in tanks.     

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.     

Evaluation of a trawl to estimate the inventory of catfish in commercial ponds

Most commercial catfish farms use multiple-batch production systems that contain fish sizes ranging from recently stocked fingerlings to fish weighing more than 1.5 kg. Currently, there are no accurate and cost-effective techniques to estimate pond inventories of catfish. Three trials were conducted in earthen catfish ponds with a 12 m × 8 m trawl (bar mesh at mouth of 3.8-cm; 2.54-cm at cod end). The first two trials included trawling with and without feed as bait in 4-ha commercial catfish ponds (Trial 1) and in 1.6-ha experimental ponds (Trial 2). In Trial 3, the trawl was pulled three times without feeding in 1.6-ha experimental ponds. Mean individual weights and size distributions of catfish caught by the trawl were statistically similar to those of catfish caught by the seine (Trial 1) and to stocking data (Trial 2). Single pulls with the trawl resulted in 73% error in estimated fish inventories in Trial 3. However, if pulled two times, the estimated catfish inventory error dropped to 7%, more accurate than other inventory methods, but was variable (coefficient of variation = 186%). The trawl appears to have potential as a means to sample commercial catfish ponds to estimate means and frequency distributions of fish size, but additional refinement and correction would be needed for it to be used reliably to estimate total pond inventory.