The objective was to evaluate the welfare implications of electrical stunning prior to gill-cutting of farmed African catfish as an alternative to live chilling in combination with gutting. Electroencephalogram (EEG) and electrocardiogram (ECG) recordings, in combination with observation of behaviour and responses to noxious stimuli, were used to assess brain and cardiac function in African catfish (body-weight 1571 ± 362 g [mean ± standard deviation], 32 males and 26 females). In the first experiment, the minimum electrical current required to induce a general epileptiform insult by head-only stunning was determined. The individual catfish were fixed in a specially designed restrainer, and applied voltages of 150 V, 200 V, 250 V, 300 V or 350 V (50 Hz AC) were delivered via scissor-model stunning tongs for approximately I s. A general epileptiform insult was observed in 31 fish, for which a successful EEG recording was obtained using 362 ± 32 V, 629 ± 180 mA for 1.2 s. The durations of the tonic, the clonic and the exhaustion phases were 8 ± 3 s, 12 ± 7 s and 7 ± 5 s as measured by EEG, respectively; a distinct exhaustion phase was not clear in II fish. The total duration of the insult was 23 ± 8 s. After the insult the fish recovered. The heart rate was 63 ± 29 beats min I prior to stunning. After stunning, the ECG revealed extrasystole and was irregular. By using an average current of 629 ± 180 mA (at approximately 360 V, 50 Hz AC), at least 91% of fish are effectively stunned with a confidence level of 95%. In the second experiment, the behaviour of 10 individual catfish, which were able to move freely in water, was observed following head-only stunning (370 V). The durations of the tonic, clonic and exhaustion phases in free-swimming fish were II ± 8 s, 20 ± 5 s and 23 ± 20 s, respectively. All fish recovered. In the third experiment, a group of seven catfish was head-only stunned followed by gill-cutting to kill them as a second procedure (ie after recovery from head-only stunning). No brain activity was seen on the EEG 12 ± 5 s after stunning. However, two fish showed responses to noxious stimuli after 2 min and 5 min. A second group of seven catfish was gill-cut only. They responded to noxious stimuli for at least 15 min. The blood loss was 1.2% and I.0% of live weight for the first and second group, respectively. It may be concluded from our results that African catfish are effectively stunned for 23 ± 8 s with a current of 629 ± 180 mA for 1.2 s, after which they recover. Since evoked responses may remain for at least 5 min after stunning and gill-cutting, we recommended that the stunning and killing procedure should be optimised.

The genus Clinostomoides Dollfus, 1950 was erected to accommodate a single worm from Ardea goliath sampled in the Belgian Congo. The specimen was distinguished from other clinostomids by its large size and posterior genitalia. In the following years, metacercariae of Clinostomoides brieni, have been described in Clarias spp. in southern and western Africa. A few authors have referred to Clinostomum brieni, but all such usages appear to be lapsus calami, and the validity of Clinostomoides remains widely accepted. In this study our aim was: position C. brieni among the growing clinostomids molecular database, and redescribe the species with emphasis on characters that have emerged as important in recent work. We sequenced two nuclear (partial 18S and ITS) and one mitochondrial marker (partial cytochrome c oxidase I) and studied morphology in metacercariae from hosts and localities likely to harbour the type species (Clarias spp., Democratic Republic of the Congo, South Africa). Phylogenetic analysis shows C. brieni belongs within Clinostomum Leidy, 1856. We therefore transfer C. brieni to Clinostomum, amend the diagnosis for the genus Clinostomum and provide a critical analysis of other species in Clinostomoides, all of which we consider species inquirendae, as they rest on comparisons of different developmental stages.

An eight-equation partially-recursive econometric model is specified to indicate the effects of catfish advertising on product awareness, beliefs, attitude and consumption. Results indicate the ad campaign in its first year (i) increased consumers' awareness of farm-raised catfish 15 percent, (ii) improved consumers' perceptions of and attitude toward catfish 3 to 6 percent, and (iii) increased at-home and restaurant purchases of catfish 12 to 13 percent. The response to the ad campaign is broken down into an “attitude effect” and a “reminder effect” to determine the relative behavioral importance of the affective and cognitive components of the ad copy. Model simulations suggest primacy of the reminder effect, implying the factual content of the ads had less impact on behavior than the mere presence of the ads.

A multiperiod programming model was used to simulate the effects of lower marginal income tax rates, the soil and water conservation deduction, and the cash tax accounting option on firm growth for a “representative” farm operating in the Alabama Black Belt region. Results show the lowered marginal income tax rates associated with the Economic Recovery Tax Act (ERTA) of 1981 provide a positive growth stimulus to the modeled firm as measured by accumulated net worth over a 10-year planning horizon. The soil and water conservation deduction in general provides greater tax relief to the modeled firm than either the ERTA income tax rate changes or the cash tax accounting provision. Important complementary and substitute relationships were found to exist between marginal income tax rates and the various tax provisions studied, implying care must be exercised when attempting to evaluate the impact on farm firms of changes in tax policy.

Increasing concentration in food processing has important economic implications for agricultural producers and consumers. This paper addresses the issue by focusing on a case where pure monopsony conditions appear to hold–catfish processing in West Alabama. Farm-level impacts of the market power imbalance are described via a six equation theoretical model. Results show price elasticity of farm supply governing the economic incentive to the processor for exploiting its market power: less (more) elastic supply implies greater (lesser) divergence between competitive and monopsony price. The theoretical model is operationalized using an indirect procedure recently suggested by Houck for estimating farm level supply elasticities. Based on these supply elasticities and historical prices, the model predicts a 12-35 percent potential reduction in prices received by West Alabama producers as a result of market power imbalance.

Harvest response to production and asymmetric price risk was analyzed using an ordinary least squares model. Statistically significant responses to production-quality and output price risk were indicated. Results suggest that alternative pricing strategies designed to reduce risk may alter harvest response and decrease month to month harvest variability.

Cost, returns, and economies of scale for small, medium and large catfish farms with recirculating ponds are presented for the upper Texas coast. Internal rates of return are 0.150, 0.183 and 0.219, respectively. Total investment is higher than farms with static ponds but investment per unit production capacity is 7 percent to 16 percent lower. Average total cost per pound is between $0,565 and $0,541, (11 percent-20 percent lower than farms using current technology). These results have implications for regional comparative advantage of catfish production as well as incentive for adoption of new technology in conventional ponds.

Off-flavor in catfish restricts farm marketings 10 to 45% depending on the season. The economic impact on society of this imposed supply restriction depends, in part, on the elasticity of demand for catfish. Econometric estimates based on disaggregated processing plant data indicate an elastic demand at the processor level but an inelastic demand at the farm level. Short-run social welfare gains from the elimination of off-flavor are estimated to equal 12.0% of farm revenues ($10.0 million in 1983). The inelastic demand for catfish at the farm level, however, means that most of the societal gains will accrue to individuals beyond the farm gate. Thus, an economic justification exists for public sector funding of off-flavor research.

Channel catfish raised in the southern United States require two growing seasons to reach market size. Growing seasons are separated by a cool period of about 3 months when feed intake and growth are greatly reduced. A cool-weather feeding strategy to improve feed intake, growth or health of catfish might improve survival and reduce the time needed to achieve market size. We conducted a feeding trial with channel catfish at a suboptimal temperature (15°C) to determine the effects of supplementing diets with either a dairy/yeast prebiotic or flaxseed oil (high in 18:3n-3) compared with a control with soybean oil (high in 18:2n-6). The trial was conducted in recirculating systems with 1140-l tanks containing 100 fish each (mean initial weight 61.4 g±0.43 s.e.m.). A 28%-protein basal diet was supplemented with 20 g/kg cellulose and 20 g/kg soybean oil (SBO, control), 20 g/kg cellulose and 20 g/kg flaxseed oil (FLAX) or 20 g/kg of a dairy/yeast prebiotic and 20 g/kg soybean oil (PREB). Fish were fed once daily to satiation and weighed every 3 weeks to track growth. Hematology, non-specific immune responses, proximate and fatty acid composition of muscle were determined to assess diet effects. Catfish-fed FLAX or PREB had higher weight gain, feed consumption and lysozyme activity than fish fed SBO. Total n-3 fatty acids in muscle were higher in fish fed SBO or FLAX than those fed PREB. Total n-6 long-chain polyunsaturated acids were higher in muscle of fish fed PREB than those fed SBO. Fatty acids in the PREB and SBO diets were similar, so the PREB appeared to increase elongation and desaturation of n-6 fatty acids in muscle. Flaxseed oil and the dairy/yeast prebiotic both have potential to increase catfish performance at a low temperature.

Regulation of insulin-mediated resumption of meiotic maturation in catfish oocytes was investigated. Insulin stimulation of post-vitellogenic oocytes promotes the synthesis of cyclin B, histone H1 kinase activation and a germinal vesicle breakdown (GVBD) response in a dose-dependent and duration-dependent manner. The PI3K inhibitor wortmannin abrogates recombinant human (rh)-insulin action on histone H1 kinase activation and meiotic G2–M1 transition in denuded and follicle-enclosed oocytes in vitro. While the translational inhibitor cycloheximide attenuates rh-insulin action, priming with transcriptional blocker actinomycin D prevents insulin-stimulated maturational response appreciably, albeit in low amounts. Compared with rh-insulin, human chorionic gonadotrophin (hCG) stimulation of follicle-enclosed oocytes in vitro triggers a sharp increase in 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DHP) secreted in the incubation medium at 12 h. Interestingly, the insulin, but not the hCG-induced, maturational response shows less susceptibility to steroidogenesis inhibitors, trilostane or dl-aminoglutethimide. In addition, priming with phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) or cell-permeable dbcAMP or adenylyl cyclase activator forskolin reverses the action of insulin on meiotic G2–M1 transition. Conversely, the adenylyl cyclase inhibitor, SQ 22536, or PKA inhibitor H89 promotes the resumption of meiosis alone and further potentiates the GVBD response in the presence of rh-insulin. Furthermore, insulin-mediated meiotic maturation involves the down-regulation of endogenous protein kinase A (PKA) activity in a manner sensitive to PI3K activation, suggesting potential involvement of a cross-talk between cAMP/PKA and insulin-mediated signalling cascade in catfish oocytes in vitro. Taken together, these results suggest that rh-insulin regulation of the maturational response in C. batrachus oocytes involves down-regulation of PKA, synthesis of cyclin B, and histone H1 kinase activation and demonstrates reduced sensitivity to steroidogenesis and transcriptional inhibition.

This study examines the dynamic effects of grain prices and energy prices on catfish feed prices and the price of food-sized catfish at the farm level. Using the autoregressive distributed lag model and bounds testing procedure, a long-run relationship between feed and farm prices and their determinants was confirmed. Given the effect of corn and soybean meal prices on catfish feed prices, and catfish fish feed prices on farm prices, the long-run responsiveness of feed prices to a percentage increase in U.S. ethanol production is 0.325, and the responsiveness of catfish farm prices is 0.064. Although both feed and farm prices increase with ethanol production, the relatively small responsiveness of farm prices when compared with feed prices suggests that catfish farmers are worse off. Results are conditional on ethanol production causing an increase in grain prices.

The generalized dynamic Rotterdam model was used in estimating U.S. demand for disaggregated catfish. The overall goal was to examine habit persistence in consumption and to determine the adjustment process in demand. Results indicated that it took up to 1 month for catfish-product demand to fully adjust to changes in expenditures and prices. Additionally, habit persistence played a role in demand where present consumption of a given product was positively affected by past consumption of that product. Consequently, U.S. catfish demand was significantly more elastic in the long-ran.

This study seeks to identify interproduct relationships between domestic catfish and a representative selection of imported seafood. In doing so, this study uses multivariate cointegration and structural analyses. Multivariate cointegration analysis suggests that six imported seafood product groupings form a common market with domestic catfish. Structural analysis reveals that 1) domestic and imported catfish are net and gross quantity substitutes; 2) domestic catfish and imported seafood are normal goods; 3) six imported seafood products are identified as gross quantity substitutes for domestic catfish; and 4) according to the derived Allais coefficients, interaction intensities of imported seafood for domestic catfish (from greatest to least) are as follows: tuna, shrimp, salmon, tilapia, catfish, and trout.

The organogenesis of the digestive system was described in the Amazonian pimelodid catfish species Pseudoplatystoma punctifer from hatching (3.5 mm total length, TL) to 41 days post-fertilization (dpf) (58.1 mm TL) reared at 28°C. Newly hatched larvae showed a simple digestive tract, which appeared as a straight undifferentiated and unfolded tube lined by a single layer of columnar epithelial cells (future enterocytes). During the endogenous feeding period, comprised between 20 and 96 h post-fertilization (3.5 to 6.1 mm TL), the larval digestive system experienced a fast transformation with the almost complete development and differentiation of most of digestive organs (buccopahrynx, oesophagus, intestine, liver and exocrine pancreas). Yolk reserves were not completely depleted at the onset of exogenous feeding (4 dpf, 6.1 mm TL), and a period of mixed nutrition was observed up to 6 to 7 dpf (6.8 to 7.3 mm TL) when yolk was definitively exhausted. The stomach was the organ that latest achieved its complete differentiation, characterized by the development of abundant gastric glands in the fundic stomach between 10 and 15 dpf (10.9 to 15.8 mm TL) and the formation of the pyloric sphincter at the junction of the pyloric stomach and the anterior intestine at 15 dpf (15.8 mm TL). The above-mentioned morphological and histological features observed suggested the achievement of a digestive system characteristic of P. punctifer juveniles and adults. The ontogeny of the digestive system in P. punctifer followed the same general pattern as in most Siluriform species so far, although some species-specific differences in the timing of differentiation of several digestive structures were noted, which might be related to different reproductive guilds, egg and larval size or even different larval rearing practices. According to present findings on the histological development of the digestive system in P. punctifer, some recommendations regarding the rearing practices of this species are also provided in order to improve the actual larval rearing techniques of this fast-growing Neotropical catfish species.

Macrogyrodactylus spp. from the gills of Clarias gariepinus in Zimbabwe and Kenya, and C. anguillaris in Senegal were identified using haptoral sclerite morphology and by sequencing the nuclear ribosomal DNA internal transcribed spacers (ITS) 1 and 2, partial 18S and the complete 5·8S rRNA gene. A molecular phylogeny was constructed using all sequenced Macrogyrodactylus species to date. Based on morphology, Macrogyrodactylus congolensis, M. heterobranchii, M. clarii, and M. karibae were identified, with one specimen from Zimbabwe displaying morphological features that were intermediate between M. heterobranchii and M. clarii. In the intermediate form, the partial 18S and ITS1 sequence was identical to that of M. clarii while the remaining ITS1 and complete ITS2 region was almost identical to M. heterobranchii as was the partial cox1 fragment, thus strongly suggesting a hybrid origin. At present, the catfish host of M. heterobranchii and M. clarii do not co-occur in southern Zimbabwe; this hybridization event is therefore proof of historical sympatry of both fish species.

The swimming, air-gaping, and agonistic behaviours of Heterobranchus longifilis (318 ± 67 mm) were examined while fish were in a fasted state under 12L:12D and variable group size (2, 5, 10 and 15 fish) in a 1000-L aquarium. Fish exhibited a predominantly nocturnal activity pattern independent of group size. A diurnal peak of activity occurred, however, at the usual feeding time. A reduction in frequency of agonistic interactions was observed in larger groups. Five fish were then observed under 72L:0D and 0L:72D. The nocturnal activity pattern remained, contrary to the diurnal peak, and was independent of the duration of illumination or darkness. These results suggest the absence of biological clock in H. longifilis, although fish may somehow be influenced by past feeding experience. Behavioural plasticity in this species may provide potential for aquaculture in northern latitudes.

The ability of the fish industry to provide a continuous supply of fish protein depends on both proper biosecurity and strategies to significantly reduce the risk of infectious diseases. Vaccination is a safe and effective means to prevent disease and to increase the productivity and profitability of farmed fish. Vaccines are likely to be the prime prophylactic measure of the future because of rapidly developing advances in fish vaccine technology and producer acceptance. The efficacy of a vaccine is influenced by a variety of factors that must be considered in the development of vaccination strategies for fish. This review highlights some of these factors. The response to a modified live vaccine against Edwardsiella ictaluri is used for illustration.

Over a 3-year period at the Sukamandi station (West Java, Indonesia), 107 Pangasius hypophthalmus females were selected on the basis of a modal oocyte diameter greater than 1.0 mm and treated with either Ovaprim (n = 97) or hCG (n = 10) to induce oocyte maturation and ovulation. The two hormonal treatments led to similar results in terms of ovulation rate (88 and 90 %), hatching rate (72 ± 25 and 82 ± 11 %) and relative fecundity (171000 ± 73000 and 128000 ± 60000 ova·kg–1, with Ovaprim and hCG, respectively). The latency period between the last hormone injection and ovulation was negatively correlated to water temperature but showed important variations at a same temperature depending on individual females (e.g. between 5 and 11 h at 28–29 °C). The ovulation time was therefore difficult to predict accurately in this species. The assessment of the viability of ova retained in the ovarian cavity after ovulation showed that the process of overripening occurs rapidly in P. hypophthalmus. The overall quality of ova began to decline as early as 2 h after ovulation and, after 3 h, hatching rates decreased and the proportion of deformed larvae increased significantly in comparison to those observed at the time of ovulation. In some individual females this process occurred even more rapidly, with a sharp decrease in hatching rates between 1 and 2 h post-ovulation. The duration of ova survival did not appear to depend on the type of hormone treatment used to induce ovulation (Ovaprim or hCG). For optimized gamete management in hatcheries, it is therefore recommended to check carefully the females for the occurrence of ovulation (between 3 and 11 h after the last hormone injection, depending on water temperature) and to strip and fertilize the eggs less than 2 h thereafter.

Both in Indonesia and Vietnam, larval rearing of Pangasius hypophthalmus remains problematic due to the variable and generally low survival rates obtained. The first week represents the most critical period for these larvae and up to now, cannibalistic behaviour was considered as the main cause of mortality. In the present study, two experiments were carried out in order to better understand the evolution and causes of mortality of P. hypophthalmus larvae from hatching up to 8 d of age and to find measures to improve survival rates. The first experiment was designed to evaluate the importance of cannibalism and differences in mortality when larvae from two different females were reared either in groups of 30 individuals or in isolated condition (30 larvae reared separately). In both cases, the culture was carried out either with or without antibiotic. The aim of the second experiment was to test oxytetracycline and different disinfectants (chloramine-T, formalin and ‘formalin + malachite green oxalate’) at different dosages in order to prevent bacterial outbreaks in the culture. The results indicated that the survival rates of P. hypophthalmus larvae was dependent on the initial quality of larvae or eggs and that larval mortality was more a consequence of pathogenic infection than a direct effect of cannibalism. The present study demonstrated that the survival rates of larvae were systematically improved when rearing was carried out in water containing antibiotic (oxytetracycline at a dose of 5 to 20 mg·L−1). Survival rate and final mean body weight of larvae as high as those obtained using antibiotic were also reached with applications of disinfectants such as chloramine-T and formalin. The use of these disinfectants is recommended for commercial P. hypophthalmus hatcheries.