George S. Libey

Effect of Triploidy on Growth and Gonad Development of Channel Catfish

Abstract Diploid (2n = 58) and triploid (3n = 87) channel catfish Ictalurus punctatus were reared indoors in circular fiberglass tanks equipped with rotating disc biofilters. Triploids were significantly heavier than diploids at 8 months of age and older. Triploid male and female channel catfish also had smaller gonads with altered histology. Triploids converted feed more efficiently, and may provide greater profits in commercial catfish culture than diploids.

Induction of Triploidy in Channel Catfish

Abstract Triploidy was induced in channel catfish (Ictalurus punctatus) by cold-shocking fertilized eggs at 5 C for 1.0 hour starting 5 minutes after fertilization. Chromosome counts from lymphocytes and kidney tissues showed 100% triploidy in the cold-shocked group and 100% diploidy in the controls. Hatching success of eggs cold-shocked 1.0 hour was 79% compared to 89% in the controls. Cold shocks longer than 1.0 hour caused 100% mortality.

Polyploidy induced by heat shock in channel catfish

Abstract Female channel catfish were induced to ovulate in fiberglass raceways by administering a total dose of 11 mg/kg of carp pituitary extract in two injections. Eggs were handstripped and fertilized with minced testis from donor males. First cleavage division was visible and occurred around 90 min postfertilization. Eggs were heat shocked in 56-1 aquaria at 80, 85, or 90 min postfertilization at temperatures of 40, 41, 42, or 43°C for a duration of 1, 2, 3, or 4 min. Eggs subjected to heat shock produced tetraploids, triploids, diploids, and mosaics. Ploidy level was determined by counts of chromosome preparations of five embryos per treatment combination sampled prior to hatching. Eggs stressed at 42 and 43°C had nearly complete mortality in shocks longer than 1 min. Forty-one degrees and 3 min duration induced tetraploidy in 62% of the embryos sampled. In shocks of 3 and 4 min at 40 and 41°C, postfertilization time did not significantly affect rates of polyploid generation. Hatchability was low in treatments which induced tetraploidy but no abnormalities were found among sampled embryos. Live fry from these groups are being raised for further study.

Evaluation of a trickling biofilter in a recirculating aquaculture system containing channel catfish

Abstract Six 1060 liter recirculating culture systems were tested, differing only in the quantity of filter medium and the recirculating flow rate. After a preliminary loading trial to determine approximate carrying capacities, 45·4 kg of channel catfish Ictalurus punctatus averaging 35·6 cm were stocked in each system. After 15 weeks, final loadings ranged from 67 to 85 g liter −1 system capacities (85–109 g liter −1 culture tank densities). Water quality was good to excellent when the packed towers contained the medium. Dissolved oxygen was probably the most limiting factor of total production. However, the rate of production was influenced by the combined effect of concentrations of dissolved oxygen, NH 3 N and/or NO 2 − N otherwise considered safe.

Oxygen recharge and ammonia stripping capabilities of various closed culture configurations

Abstract A packed tower (trickling filter), empty, half full and full of a medium (styrofoam packing material) and a rotating biological contactor (RBC, rotating disc) were tested at various recirculating flow rates, with and without supplemental aeration, to determine oxygen recharge and ammonia stripping capabilities. Oxygen recharge capabilities increased with increasing flow rates, but at different rates for each filter. Oxygen recharge efficiencies decreased as flow rates increased in the half full and empty towers, were about constant for the full tower and increased in the RBC. Oxygen recharge capabilities were significantly increased with the addition of surface agitation; greater than the sum of the component contributions. With supplemental aeration, the full tower with a recirculation flow of 45·4 liters/min was most efficient and capable of supplying the most oxygen. Ammonia stripping was found to be insignificant in all systems tested.