Catfish aquaculture

This article deals with the biology, broodstock management, seed production techniques and grow-out culture practices in C. macrocephalus

Grow-out culture of the Asian catfish Clarias macrocephalus (Gunther)

Asian catfish Clarias macrocephalus is an esteemed food fish especially in Southeast Asia due to its tender and delicious meat. This commodity constitutes a valuable fishery for small-scale fishers in the region and has a great potential for aquaculture. The important considerations in the grow-out culture of catfish are reliable water supply, soil with good compaction properties for dike construction, supply of fingerlings, feeds, labor, pond supplies and technology assistance. The farm must also be accessible by road, near to market facilities and has a peaceful environment. Rearing catfish in ponds is the most popular and commonly practiced. The pen culture is a system fully enclosed by nets on all sides but utilizes the dug-out pond, dam or lake bed as bottom enclosure. Tanks in abandoned old hatcheries with freshwater source can be used for catfish culture. In the cage culture system the stock is fully enclosed by nylon nets on all sides and bottom similar to an inverted mosquito net installed in suitable areas like reservoirs, dams, lakes and dug-out ponds. The rice-fish (catfish) culture is also practiced where the rice pond canals are utilized to retain water at 1-2 m depth to provide shelter to the fish while the rice plot maintains 10-20 cm water depth. For the stock, select fingerlings that are active, healthy and uniform in size. Handling of fish stock is important to avoid mortality due to stress during harvest, sorting, counting and transport. Furthermore, stocking of fish is recommended during the cooler part of the day. Catfish fingerlings stocking density is about 5 to 20 pcs/m2 depending on the water supply and support facilities of the farm. The catfish, C. macrocephalus, requires a substantial amount of dietary protein for growth. For this species a formulated diet with crude protein (CP) of 34%, moist diet (trash fish or blanched chicken entrails plus rice bran or cooked broken rice), and a combination of pellet feeds (50%) and moist diet (50%) have been tested and acceptable for the grow-out culture. Economic evaluation based on a grow-out culture in pond with an area of 1,000 m2 showed that feeds and fingerlings are the major variable costs. The net income, return on investments and payback period, respectively range from PhP22,972-PhP35,741, 80-122% and 0.8-1.2 years when using pellet, moist feed or a combination of these feeds. Feeding using formulated diet has an advantage of convenience, quality and quantity over moist diet which has issues such as inconsistent supply, storage requirement and fouling the rearing water

Induction of oocyte maturation and ovulation in the freshwater Asian catfish, Clarias macrocephalus by LHRHa and pimozide

Three experiments were conducted to determine the effects of a simultaneous injection of varying doses of luteinizing hormone-releasing hormone analogue (LHRHa; 0.005–0.10 μg)/body weight (BW) in combination with a fixed dose of pimozide (PIM; 1 μg)/g BW on oocyte maturation and ovulation in the catfish Clarias macrocephalus (body weight: 39 to 167 g). This was done by monitoring the development and size of the oocytes after hormone injection at various sampling intervals for 48 hours. In Experiment I (March 1989), only the fish injected with 0.10 μg LHRHa + 1μg PIM/g BW underwent final maturation and ovulation. However, oocyte maturation and ovulation were observed in all treated fish in Experiment II (April 1989). Oocyte maturation and ovulation were also induced except in fish injected with the lower dose combination (0.005 μg LHRHa + 1 μg PIM/g BW) or PIM alone (1 μg/g BW) in Experiment III (September 1989). No maturation was observed in all vehicle-injected control fish in the three experiments. Mean egg diameter of fish that were induced to mature increased during ovulation but remained similar in size in fish which did not undergo final maturation. This study showed that captive C. macrocephalus can be induced to undergo oocyte maturation and ovulation at 15 to 16 h after a simultaneous injection of 0.01 to 0.10 μg LHRHa + 1 μg PIM/g BW

Withdrawal of exogenous 17-alpha methyltestosterone causes reversal of sex-inversed male grouper Epinephelus suillus (Valenciennes)

The protogynous hermaphrodite groupers Epinephelus suillus were given bi-weekly injections of 17 alpha-methyltestosterone (MT) intramuscularly for three to six months. Spermatogenesis occurred after three months of MT treatment while spermiation was observed after five to six months of MT treatment in larger fish. Neither cannulated tissue nor milt was obtained when the remaining fish were sampled four months after withdrawal of exogenous MT. However, vitellogenic eggs (size range = 0.34 to 0.56 mm) were cannulated eight months after termination of MT treatment. Presence of eggs in fish which previously had expressible or cannulated milt indicates that the sex-inversed male E. suillus reverted back to the female condition upon withdrawal of exogenous MT. This information is useful in the line production of functional males which is the limiting factor in induced breeding of groupers

Effects of unilateral eyestalk ablation on ovarian histology and oocyte size frequency of wild and pond-reared Penaeus monodon (Fabricius) broodstock

Effects of eyestalk ablation on ovarian maturation of wild and pond-reared Penaeus monodon were determined to compare their reproductive potential. This was done by counting the oocyte size frequency in four regions of the ovary and comparing the percentage of each cell type present at each stage of maturation per group. Sampling of ablated prawns was done during three maturation or spawning periods within the first molt cycle after ablation. It took 5 and 14 days for wild and pondreared prawns, respectively, to show signs of ovarian maturation after ablation. Percentage of proliferating cells, the smallest germinal cells in the prawn ovary, was higher in wild unablated (8.3%) than ablated (2.5–5.0%) groups. Significant differences were observed in all cell types at different stages of maturation. In both unablated and ablated prawns, there was a uniform development of the whole ovary and similar occurrence of atresia at all stages. The presence of bigger oocytes in the ovaries of ablated prawns sampled after spawning provided histological evidence for lower number of eggs per spawn and faster rematuration

Suitability of different formalin-containing fixatives for the eggs of freshwater Asian catfish Clarias macrocephalus (Gunther)

The suitability of different formalin-containing fixatives was tested for the eggs of the catfish (Clarias macrocephalus) by comparing the osmotic pressure of several fixatives with catfish plasma and measuring the size of the eggs at several intervals after fixation. The test solutions consisted of Gilson fluid, 0.5% to 10% buffered formalin, 0.1% to 1% unbuffered formalin with 0.7% sodium chloride (NaCl) and 0.1% to 1% unbuffered formalin with 0.9% NaCl. The osmotic pressure of 1% phosphate-buffered formalin was not significantly different from the catfish plasma, hence it was considered to be the most suitable of all the fixatives tested. Measurement of catfish eggs can be done within 0.5 to 120 hours after fixation in this solution because the rate of swelling (4% to 11% of the size of fresh samples) has been determined. This information is important in induced breeding work of catfish, especially on studies involving the use of egg size

Growth And Yield Of Asian Catfish Clarias Macrocephalus (Gunther) Fed Different Growth-Out Diets

Juveniles of the Asian catfish Clarias macrocephalus (3.6±0.17 g; 78.0±0.09 mm) were fed one of four diets: a laboratory-formulated diet of 18.9% (Diet 1) or 34.2% (Diet 2) protein, a com- mercial feed pellet of 28.9% protein (Diet 3) or a diet of 80% blanched chicken entrails and 20% rice bran (31.7% protein; Diet 4). After 120 days of culture, catfish fed Diet 2 grew significantly better (p0.05). Catfish fed Diet 2 had the highest apparent lipid retention (131.7%). The protein efficiency ratio was lowest (1.3) in Diet 2, but did not differ significantly from Diets 1 and 3. Catfish fed Diet 4 were fatty and had a lower crude protein content. Results suggest that C. macrocephalus fed 34.2% crude protein have a significantly higher weight and total yield. Further, a taste test showed that odor, flavor and appearance did not differ amongst the diets

Research on freshwater fishes

Studies on tilapias focused on the refinement of strain comparison methods, refinement and pilot-testing of broodstock improvement procedure, selective breeding and evaluation of red tilapias, genetic variability determination in hatchery-bred tilapia and the development of criteria for tilapia fingerling quality assessment. On carps, feeding of bighead carp (Aristichthys nobilis) to enhance reproductive performance was done and stunting was applied as a technique in broodstock development. Studies on the tolerance of bighead carp fry to low salinities were conducted. Free-living nematodes were tested as alternative larval food. The culture potential of grass carp in lake-based cages was also determined. Research on the native catfish (Clarias macrocephalus) focused on endocrine studies during the final stages of maturation. Hatchery techniques were refined by identification of factors that increase fry production. Practical diets were developed for broodstock, hatchery, nursery and grow-out phases. A collaborative project on the ecological impact of African catfish (C. gariepinus) introduction in natural waters was undertaken. The occurrence of EUS (epizootic ulcerative syndrome) among wild fishes in Laguna Lake decreases the marketability of both wild and cultured fishes from the lake. Hence, the bacteria and virus associated with EUS and their virulence, modes of disease transmission, developmental stages of dermal lesions and hematological changes in severely affected fish were studied. Laguna Lake, where fish catch and aquaculture production contribute significantly to the country s total freshwater fish production, has been the focus of extensive ecological research in collaboration with other local and foreign research and academic institutions

Ovarian maturation stages of the wild giant tiger prawn, Penaeus monodon Fabricius

SEAFDEC Aquaculture Department Contribution No. 233.A qualitative and quantitative study of the ovarian maturation stages of wild-caught Penaeus monodon was conducted to refine the existing method of staging. For industrial purpose, measuring the ovarian width at the first abdominal region can minimize arbitrariness in staging. A width of 20 mm indicates readiness for spawning while reproductive performance is improved when ovarian width is 30 mm or more. Based on histology, the usual 6 to 8 stages of development can be reduced to four stages: previtellogenic, vitellogenic, cortical rod, and spent. The previtellogenic stage (P) is characterized by the predominance of oogonia and primary oocytes in the chromatin nucleolus and/or perinucleolus stage. The vitellogenic stage (V) is marked by the presence of yolky oocytes. The cortical rod stage (C) is distinguished by the appearance of yolky oocytes with spherical or rod-like bodies at the peripheral cytoplasm. The spent stage (S) can be distinguished by the presence of few oocytes with yolky substance and/or cortical rods, thicker layers of follicle cells, and few darkly-stained, irregularly shaped primary oocytes. Individuals classified as stages II+ and III+ showed similarity in size and shape of all lobes in the posterior thoracic region, and histologically, corresponded to the revised stages V and C, respectively. Histochemical staining shows that glycoproteins and lipids are absent in the primary oocytes and present in yolky oocytes. Glycoproteins but not lipids occur in the cortical rods. Analysis of variance showed significant differences in mean gonad weight and gonadosomatic index values but not in the mean body length and body weight values in stages P to C. Uniformity in the number, stage and composition of oocytes in the four regions of the ovary at each stage showed that stage of ovarian maturity in wildprawns can be represented by any region of the ovary. Differences in the oocyte size frequency and mean values of average and maximum oocyte diameter in the four stages showed that these are good indicators of stage of maturation in wild P. monodon

The in vitro effects of cyclic nucleotides, cyanoketone, and cycloheximide on the production of estradiol-17 beta by vitellogenic ovarian follicles of goldfish (Carassius auratus)

The effects of human chorionic gonadotropin (HCG), forskolin, cyclic nucleotides, the phosphodiesterase inhibitors IBMX and theophylline, cyanoketone, and cycloheximide on the production of estradiol-17β by isolated ovarian follicles of vitellogenic goldfish (Carassius auratus) were examined using 18-hr incubations. HCG and all test agents which are known to increase intracellular concentrations of cAMP significantly stimulated the production of estradiol-17β. However, dibutyryl cGMP was unable to stimulate estradiol-17β production at any concentration used (1–10 mM). Cyanoketone at a concentration of 1 μg/ml completely blocked forskolin-induced estradiol-17β production. Even in the presence of cyanoketone, however, forskolin stimulated conversion of exogenous testosterone to estradiol-17β in a dose-dependent manner, suggesting the involvement of an adenylate-cyclase system in the induction of aromatase activation by vitellogenic follicles of goldfish. Cycloheximide also completely abolished HCG-induced estradiol-17β production when this inhibitor was added within the first 1 hr after the addition of HCG. These results provide evidence that the stimulation of estradiol-17β by goldfish vitellogenic follicles in response to HCG is dependent upon the synthesis of new protein