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.     

Wading Bird Depredations on Channel Catfish Ictalurus punctatus in Northwest Mississippi

We interviewed farm managers about their perceptions of wading bird problems and conducted preliminary surveys of wading bird populations at 67 randomly selected channel catfish Ictalurus punctatus pond complexes in northwest Mississippi during December 1995. At a subsample of 24 complexes and 10 other complexes previously surveyed in 1990, we surveyed wading bird populations bimonthly throughout the year in 1996 and observed great blue herons Ardea herodias and great egrets Ardea alba feeding at catfish ponds. Seventy-five percent of farm managers questioned felt that wading birds were causing losses to their fish stocks, and 74% believed the problem was increasing. Consistent with interview results, 88% of the pond complexes surveyed had one or more wading birds present. Despite reported harassment programs by producers, great blue heron densities at 10 complexes previously surveyed in 1990 had increased by more than eightfold in 1996. Great blue heron densities varied with location, season and time of day, but the average 127-ha farm supported about 78 herons and 56 great egrets. Despite similar populations, the potential impact of these two species was quite different. Live catfish, averaging 10.3 cm in length (circa 10 g) comprised only 8% of the egret diet by weight, and most of the fish were obtained from fingerling ponds during periods when these fingerlings may be weakened by the bacterial disease, enteric septicemia of catfish. In contrast, live catfish, averaging 16 cm in length (circa 34 g), comprised 44% of the great blue heron diet by weight. Herons foraged from both fingerling and food fish ponds, primarily in the early morning and evening. Based on average population densities and foraging rates, herons at the average 127-ha farm in northwest Mississippi consumed 114,000 (circa 3,900 kg) catfish, annually. However, further studies are recommended to document production losses.     

Economic Effectiveness of Advertising Aquacultural Products:

An industry advertising program for catfish, financed by farmers' voluntary contributions on feed on $6.00 per ton, commenced April 1987. This study estimates the impacts of that program on consumers' perceptions of catfish, purchase frequency, and profitability. Results indicate the ad campaign in its first year increased consumers' perceptions of product attributes (flavor, fishy odor, and nutrition) and overall attitudes toward catfish 2-4%, and increased purchase frequencies for at home and restaurant consumption 11-12%. The increased consumer demand for catfish attributable to advertising was estimated to have generated between $0.72 and $11.04 million in additional farm income in 1988, a net return of between $0.48 and $7.46 per media dollar invested. Results highlight the free-rider problem associated with voluntary programs: the estimated benefits of the advertising compaign were enjoyed by all producers yet only a portion shared in the cost. The profitability of industry advertising coupled with the inability to withhold benefits from non-contributing members provide a rationale for replacing voluntary contributions with a mandatory program. The issue of the optimal level of industry advertising must await further research.     

Cost of regulations on US catfish farms

Understanding the economic effects of regulations on US aquaculture farms provides insights into which compliance costs create the greatest compliance burden on farms. This can further guide strategies to improve the efficiency of regulatory frameworks and potentially reduce on-farm compliance costs while maintaining adequate oversight. This study estimated the regulatory compliance burden on US catfish farms as part of a national effort to quantify the cost of regulations on US aquaculture farms. Completed survey interviews of catfish farms in the major catfish-producing states covered 63% of the total US catfish production area. Total regulatory costs of the US catfish industry were estimated at $45 million annually. Lost farm revenues (measured as the value of lost production, the value of markets lost from regulations, and the value of business opportunities lost because of regulations) were estimated to be $35 million per annum. Catfish-producing states outside the Alabama/Arkansas/Mississippi region had the highest ($2856/ha) and Alabama the lowest ($1127/ha) regulatory costs per hectare among the surveyed states. The greatest regulatory cost burden on catfish farms ($18 million) was caused by environmental regulations related mostly to the management of federally protected piscivorous migratory birds, followed by labor regulations ($12 million), and taxes/insurance ($7 million). Regulatory costs ($/kg) were 2.6 times higher on smaller (<80 ha) farms relative to larger (>300 ha) farms. Attention is needed to identify alternative regulatory frameworks that provide the same degree of regulatory oversight but are more cost-efficient.     

Economic Impact of Double‐Crested Cormorant,Phalacrocorax auritus,Depredation on Channel Catfish,Ictalurus punctatus,Aquaculture in Mississippi,USA

The Yazoo River Basin of Mississippi, USA, supports the largest concentration of hectares devoted to channel catfish, Ictalurus punctatus, aquaculture production in North America. The Yazoo Basin also supports large numbers of resident, wintering and migrating fish‐eating birds, with the Double‐crested Cormorant, Phalacrocorax auritus, implicated as the most serious depredating species. We used data from aerial surveys of numbers and distribution of cormorants in the Yazoo Basin and on commercial catfish ponds during winters (November–April) 2000–2001 and 2003–2004 to refine estimates of regional economic losses due to cormorant depredation. In both periods, the greatest monthly estimates of cormorant foraging occurred from 1 January to 31 March. Losses in terms of biomass, number, and dollar value were greater for foodfish ponds than fingerling ponds. Monthly weighted estimates of catfish consumed were 1775.3 and 1346.6 m.t. over winters 2000–2001 and 2003–2004, respectively. Total estimated losses for foodfish and fingerling ponds in 2000–2001 were $11.56 and $0.48 million, respectively, and in 2003–2004 were $5.22 and $0.40 million, respectively. Maximum dollar loss occurred during March in 2000–2001 and during February in 2003–2004. In this study, the volatility in variable production costs and nominal sales price, and distribution of cormorants on pond types and regionally were key factors in resulting economic loss estimates.     

PRODUCTIVE EFFICIENCY OF CATFISH FARMS IN CHICOT COUNTY,ARKANSAS

Technical, allocative, and cost efficiency measures of a sample of small-and medium-sized catfish farms in Chicot County, Arkansas were estimated using a weight-restricted data envelopment analysis technique. A measure of cost efficiency is used to determine operator characteristics, farm practices, and institutional support services that are likely to lead to higher levels of efficiency. Experience of the operators and extension contacts were important factors positively influencing farm level efficiency. Extension services in Chicot County generated about $5.2 million in cost savings among catfish farms or about $2,737 per contact. Importantly, higher cost efficiency of catfish farm efficiency in Chicot County, Arkansas, can be achieved by adjusting inputs used in production to optimal levels rather than by adjusting the scale of operation.     

Regulatory costs on U.S. salmonid farms

The economic effects of the implementation of regulations on aquaculture farms in the United States, while of concern, are not well understood. A national survey was conducted of salmonid (trout and salmon) farms in 17 states of the United States to measure on‐farm regulatory costs and to identify which regulations were the most costly to this industry segment. The response rate was 63%, with a coverage rate of 94.5% of the U.S. production of salmonids. The regulatory system resulted in increased national on‐farm costs of $16.1 million/year, lost markets with a sales value of $7.1 million/year, lost production of $5.3 million/year, and thwarted expansion attempts estimated at $40.1 million/year. Mean farm regulatory costs were $150,506/farm annually, or $2.71/kg; lost markets with annual sales values of $66,274/farm; annual lost production of $49,064/farm; and an annual value of thwarted expansion attempts estimated at $375,459/farm. Smaller‐scale farms were affected to a disproportionately greater negative extent than larger‐scale farms. Per‐farm regulatory costs were, on average, greater for foodfish producers than for producers selling to recreational markets, but per‐kg regulatory costs were greater for those selling to recreational compared to foodfish markets. Regulatory costs constituted 12% of total production and marketing costs on U.S. salmonid farms. The greatest regulatory costs were found to be effluent discharge regulations. The majority of regulatory costs were fixed costs, but regulatory barriers to expansion precluded compensatory adjustments to the business in spite of growing demand for salmonid products. Results of this study show that the on‐farm regulatory cost burden is substantial and has negatively affected the U.S. salmonid industry's ability to respond to strong demand for U.S. farm‐raised salmonid products. Results also suggest that the regulatory system has contributed to the decline in the number of U.S. salmonid farms. While regulations will necessarily have some degree of cost to farms, the magnitude of the on‐farm regulatory cost burden on U.S. salmonid farms calls for concerted efforts to identify and implement innovative regulatory monitoring and compliance frameworks that reduce the on‐farm regulatory cost burden.     

The Economic Impact of the Catfish,Ictalurus punctatus,Industry on Chicot County,Arkansas

Abstract

This study analyzed the contribution of the catfish industry to the economy of Chicot County, Arkansas, using an input-output model. The objective was to quantify the economic contribution of the industry in terms of creating new dollars, jobs, and income to the local community. Mail surveys and personal interviews were used to collect data from catfish farmers, processors and other businesses related to the catfish industry. For farmers, the information solicited included production and marketing costs, sales and employment. Out of approximately 85 questionnaires administered to catfish farms, 44 usable questionnaires were obtained for a response rate of 52%. Businesses directly related to the catfish industry provided information on employment and sales and included: processors, seiners and haulers, pond builders, tractor and equipment dealers, and feed bin manufacturers. Other businesses with indirect ties to the catfish industry included: input supply companies, banks, fertilizer and chemical companies, auto shops, electricians, and bookkeeping firms. The survey data were used to modify the IMPLAN database for Chicot County to reflect the 2001 level of catfish production, processing and services available to support the industry. This database was then used to estimate the economic impact of the industry to the county's economy. In 2001, the 85 catfish farmers in the county operated about 7,859 ha (19,500 acres). The farm-gate value of catfish production exceeded $63 million. Employment on catfish farms was approximately 510. In addition, 59 other businesses depended on the catfish industry. Results indicated that total employment created in Chicot County by businesses directly or indirectly involved with the catfish industry was 2,665 jobs. This represented 48% of all employment in Chicot County. Total tax revenue (federal, state, and local taxes) generated from both direct and indirect catfish businesses was $22 million. Combined, the total economic impact of the catfish industry in Chicot County, including direct, indirect and induced effects, was over $384 million. The output multiplier calculated for live catfish production was 6.05. Thus, each $1 of earnings by catfish farms generated $6.05 total economic activity in the Chicot County economy. If current economic difficulties should result in contractions in catfish acreage in Chicot County by 10%, unemployment rates would increase by 2%. This study demonstrates the importance of the catfish industry to the economy of Chicot County.     

Reducing Catfish Farm Losses Due to Dockages Assessed by Processing Plants

Dockages can have a significant effect on catfish, Ictalurus punctatus, farm revenues. This study was conducted to quantify common dockages, examine seasonal and yearly variations in dockages assessed, and determine optimal production practices given various dockage scenarios. A convenience survey of invoice records from 30 commercial catfish farms and 10 processing plants provided 3686 daily catfish load records that were used to quantify dockages. A linear programming model was developed to examine optimal production practices given 11 alternative production scenarios with five size‐grading technologies subject to 24 types and levels of dockages. The survey revealed that 95% of catfish loads delivered to processing plants between 1997 and 2002 were assessed dockages that resulted in average losses of 2.45% per load or $0.066/kg of catfish marketed over the study period. Out‐of‐size discounts constituted the greatest losses. Dockage losses can be reduced by shifting either to longer‐term single‐batch production or more intensive grading. Longer‐term production results in fewer smaller fish that would incur dockage losses. However, cash flow constraints require more intensive early‐season grading. The grader choice depended on the dockage tolerance level and rate, the frequency distribution of sizes of catfish in the population, the efficiency of the grading technology, and the cost of the grading method. Larger farms minimize losses with intensive active grading (University of Arkansas at Pine Bluff grader).     

An Econometric Estimation of Market Growth for the U.S. Processed Catfish Industry

Inadequate information pertaining to the growth potential of the US. processed catfish industry has been a major factor leading to cyclical periods of excess supply or demand resulting in misal-location of resources and price instability. Better information for industry planners (e.g., producers, processors, government regulatory agencies, and university researchers) on future sales potential would assist in decreasing the misuse of resources. An econometric model of wholesale demand for US. processed catfish was developed to provide estimates of future sales under various scenarios. In addition to the standard variables included in models of demand for food items—price, income, and population—the effects of product life cycle and industry-sponsored generic advertising are quantitatively incorporated. Seasonality of demand and rigidities in marketing and consumer behavior are additional considerations explicitly modeled via monthly dummy variables and a Ner-lovian partial adjustment mechanism, respectively.
Model results indicate the impact of alternative future price scenarios on wholesale processed caffish sales. At the mean real wholesale price of $1.60 (December 1988 dollars) for whole-dressed caffish and a real generic advertising expenditure of one million dollars postulated for 1995, projected aggregate sales are 219.2 million pounds, a 23% increase over 1989 sales. Projected 1995 wholesale sales are very sensitive to price with alternative price postulations of $1.40 and $1.80 resulting in projected sales of 252.3 and 193.6 million processed pounds, respectively. An estimated 7% average increase in wholesale sales of catfish was attributed to the industry-sponsored generic advertising campaign. Model projection estimates and impacts are posed as a quantitative source of information to be used with other information in resource allocation issues faced by industry decision makers.     

Comparative Economics of US Catfish Production Strategies: Evidence from a Cross‐sectional Survey

Understanding the effects of specific management strategies on yields and economic outcomes on commercial catfish farms could provide useful guidance to catfish farmers on the most profitable sets of production practices. Data from the U.S. Department of Agriculture–National Animal Health Monitoring System (USDA–NAHMS) 2009 survey of production practices on catfish farms in Alabama, Arkansas, Louisiana, and Mississippi were used to identify five clusters of catfish farms that use various stocking densities, channel versus hybrid catfish, different aeration levels, and utilize automated oxygen sensors. The lowest production costs ($1.96/kg) were found in cluster 1 and were followed in order of increasing costs per kilogram of clusters 2 and 4 ($2.16/kg) and cluster 5 ($2.73/kg); the highest cost corresponded to cluster 3 ($2.84/kg). The lowest risk levels corresponded to the clusters with the lowest production costs per kilogram of fish and the highest risk levels to the highest production costs. This analysis demonstrated that different types of management models can achieve similar levels of production costs ($/kg), and it appears that there is not one single economically optimum way to raise catfish. The key to least‐cost production is to balance the use of inputs, their associated costs, and the yield produced to achieve economic efficiency within the farm's overall business and management model.     

The Effect of Hybrid Catfish Fingerling Prices on the Relative Profitability of Hybrid Channel Catfish

Previous studies have indicated that the price premium charged for hybrid catfish fingerlings may be a significant factor in the adoption and profitability of hybrid catfish production. An enterprise budgeting simulation analysis was developed to compare costs, risk, and effect of hybrid fingerling costs. Feed, fingerling, and total costs ($/ha and $/kg) were highest for hybrid catfish production, intermediate for NWAC‐103, and lowest for normal channel catfish production. Net returns were highest for hybrid catfish production, but breakeven prices were also highest. Risk analysis showed that downside risk (risk of losing money) was higher for hybrid production for all farm sizes. Risk‐averse farmers would not select hybrid catfish at the mean fingerling values used in the analysis. However, at hybrid fingerling prices less than $0.0081/cm, hybrid catfish production was superior in profitability and breakeven cost of production. Thus, for hybrid catfish production to be preferred economically to normal channel catfish, the price premium for hybrid catfish fingerlings can be no more than 84% ($0.0037/cm) above that of normal channel catfish fingerlings and 57% ($0.0025/cm) above that of NWAC‐103 fingerling prices.     

Effects of feeding rate and dietary protein levels on the breeding performance of female yellow catfish (Pelteobagrus fulvidraco)

Nutritional components and feeding strategies are multifarious amongst different producers, whereas they are just designed for fish farming but not suitable for improving the reproductive performance of broodfish. Yellow catfish (Pelteobagrus fulvidraco), an omnivorous species, is one of the important aquaculture fish in China. In order to improve the reproductive performance of female yellow catfish (119.86—134.54 g), four feeding strategies (0.5%, 0.75%, 1% and 1.5% BW/d) and three dietary protein levels (34%, 40% and 46%) were examined, respectively, in the two separate trials. The females with moderate feed restriction (1%) showed significant lower mesenteric fat index (MFI) and higher gonadosomatic index (GSI) than the satiation group (1.5%) and excessive feeding restriction groups (0.5% and 0.75%). Females with high MFI were difficult to be artificially propagated and showed a high mortality rate, whilst the fish at 1.0% feeding rate displayed low mortality rate and high ratios of spawned fish, as well as high percentages of fertilization and hatching. Meanwhile, the offspring of 1.0% feeding rate group showed a low malformation rate and high survival rate. Multiple spawning in the same breeding season are applied in yellow catfish to reduce the number of parent fish and increase the fry production, and gonadal recrudescence after spawning might be affected by different nutrient values including dietary protein levels. In the second trail, female yellow catfish were fed with 34%, 40% and 46% crude protein diet at 1% feeding rate for the second spawning, and the best reproductive and breeding performances were observed in the fish group with 46% crude protein diet. These results demonstrate that 1% feeding rate is optimum for the spawning and reproductive performance of female yellow catfish for the first artificial spawning, and 46% dietary protein group had the best reproductive performances in the second spawning.     

Costs of Winter Feeding of Channel‐blue (♀ Ictalurus punctatus × ♂ Ictalurus furcatus) Hybrid Catfish

Previous research has shown that winter feeding is beneficial in preventing weight loss and maintaining catfish health. Although several studies suggest the importance of winter feeding of channel catfish, Ictalurus punctatus, less is known about optimal winter feeding strategies for channel‐blue hybrid catfish (♀ Ictalurus punctatus × ♂ Ictalurus furcatus). Three winter feeding treatments (unfed, fed daily, and fed based on temperature‐threshold feeding) were each assigned randomly to four replicate 0.10‐ha earthen ponds. All ponds were stocked with large channel‐blue hybrid catfish (0.96 ± 0.40 kg) at the rate of 3409 kg/ha and fed using a slow‐sink 28% protein pelleted feed. The two feeding treatments showed significantly greater mean weight at harvest, gross yield, and growth rates than the unfed fish after the 113‐d winter trial. Partial budget analysis indicated that additional costs incurred from the additional feed, fuel, and labor costs over the winter in fed treatments offset the additional revenue from daily winter feeding. However, in the temperature‐threshold feeding treatment, additional costs were similar to additional revenues when 10‐yr average prices were used. Results were sensitive to feed prices and spring catfish prices with positive net benefits from winter feeding at fish prices above $1.58/kg and feed prices below $0.286/kg.     

Development of aquaculture financial planning system

Abstract

Economically efficient feeding levels in intensively stocked ponds might be below minimum biological feeding requirements under adverse market conditions. A catfish production function that estimated relationships between yield and stocking and feeding rates was used as the basis for estimating production relationships. Feed price boundaries were developed that allowed the feeding rate to exceed the minimum biological level but still reflected economically efficient rates over a range of catfish prices and producer risk preferences. At higher stocking densities (20,000/ha), the feed price upper bound is lower than at lower stocking densities. Producers stocking at higher rates will be less likely to maximize profit and meet minimum biological feeding requirements as feed price increases than those producers stocking at lower rates. However, if feed prices exceed the upper bounds calculated in this paper, producers should engage in feeding only at levels necessary to meet farm financial and cash flow obligations until such time as the feed price decreases.     

Economics of Intensively Aerated Catfish Ponds

The US catfish industry is evolving by adopting production‐intensifying practices that enhance productivity. Catfish producers have increased aeration rates over time, and some now use intensive rates of aeration (>9.33 kW/ha). Costs and production performance were monitored at commercial catfish farms using high levels of aeration (11.2–18.7 kW/ha) in Alabama, Arkansas, and Mississippi. A multivariate‐cluster analysis was used to identify four different management clusters of intensively aerated commercial catfish farms based on stocking density, size of fingerlings at stocking, and feed conversion ratios (FCR). Breakeven prices of hybrid catfish raised in intensively aerated pond systems were estimated to range from $1.86/kg to $2.17/kg, with the lowest costs associated with the second greatest level of production intensity. The two medium‐intensity clusters generated sufficiently high revenues for long‐term profitability. However, the least‐intensive and the most‐intensive clusters were economically feasible only when catfish and feed prices were closer to less probable market prices. Feed price, FCR, and yield contributed the most to downside risk. Intensive aeration in catfish ponds, up to the levels analyzed in this study, appears to be economically feasible under the medium‐intensity management strategies identified in this analysis.     

Costs and Risk of Catfish Split‐pond Systems

Split ponds are recently developed pond‐based aquaculture systems that allow intensification of catfish aquaculture. Successful industry‐wide adoption of newly developing technologies like split‐pond systems will depend upon their productivity and cost efficiencies. Costs and production performance of the following three split‐pond design scenarios were monitored in Arkansas and Mississippi: (1) research design developed at the Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi; (2) waterwheel design tested on commercial catfish ponds; and (3) screw‐pump design tested on commercial catfish ponds. An economic engineering approach using standard enterprise budget analysis was used to develop estimates of breakeven prices (BEPs) ($/kg) for producing foodsize hybrid catfish (♂Ictalurus furcatus × ♀Ictalurus punctatus) for each scenario. Estimates of BEPs of hybrid catfish raised in split ponds ranged from $1.72 to $2.05/kg. The cost of catfish production in split ponds was sensitive to yield, fish prices, and feed prices. Annual net cash flows from both commercial split‐pond systems were high and sufficient to make the investment profitable in the long run. Feed price, feed conversion ratio, and yield contributed the most to downside risk of split ponds.     

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.     

Fermented earthworms as a feed additive enhances non-specific immune response in catfish (Clarias gariepinus)

Catfish which is an important component of global freshwater aquaculture production is also prone to a wide range of diseases resulting in economic losses. Improvement of the immune status of catfish is a promising preventive approach to control disease. The purpose of this study was to determine the effect of fermented earthworms as a feed additive on the non-specific immune response of walking catfish (Clarias gariepinus). Earthworms were fermented by inoculation with a bacterial mixture of Bacillus spp. and Lactococcus raffinolactis. The study featured a completely randomized design, with five treatments in quadruplicate. The various treatments consisted of fermented earthworms supplemented (FE) at at 0%, 2.5%, 5%, 7.5%, and 10% (w/w). Catfish with an average weight of 15 g were stocked at a density of 50 fish per 50 L/tank, reared for 2 months, and fed thrice a day at a feeding rate of 3% of total boby weight. The parameters observed included phagocytic activity (PA), phagocytic index (PI), extracellular respiratory burst, leucocyte differentiation, super oxide dismutase (SOD), natural agglutination, leucocrit, and hematocrit. Results showed that that FE supplemented at 2.5% significantly increased the respiratory burst activity, hematocrit, PA, PI, SOD, and leucocyte differentiation (P?<?0.05) but did not affect natural agglutination. The results collectively suggest that FE as a feed additive is an effective and applicable strategy to improve the non-specific immunity of catfish.

     

The Cost of Off-Flavor

Off-flavor problems in farm-raised catfish Ictalurus punctatus increase production costs and pose inventory management problems for catfish farmers. Multiperiod mathematical programming techniques were used to test the effect of 16 different off-flavor scenarios on expected net returns above variable cost with and without cash flow restrictions. The patterns of off-flavor incidence had less effect on farm profits than whether or not fish are off-flavor during certain key months of the year. To be feasible, systems designed to purge off-flavor from catfish would need to cost less than $0.05 to $0.06/kg (if cash flow is not a consideration) or $0.04/kg to $0.25/ke (with cash flow considerations).