An Evaluation of Natural and Artificial Dietary Lipid Sources on Egg Quality and Fry Production in Channel Catfish (male) X Blue Catfish (female) Hybridization

Abstract

Hybrid catfish (channel catfish Ictalurus punctatus? x blue catfish I. furcatus?) display many characteristics that are favorable to aquaculture production such as increased growth, resistance to disease, higher dress out and ease of seining. The implementation of this hybrid variety into full scale aquaculture production is limited mainly by the difficulties involved with spawning, incubation and larval rearing. One of the confounding stages that has high mortality rates is the complex developmental steps that take place after fertilization. In this phase, the developing embryo must obtain its nutrients and structural components for development from the egg reserves. Therefore, to maximize the survival of these hybrid embryos through hatch, a high quality egg should be supplied by the female. This study was conducted in an attempt to isolate nutritional lipids that lead to high quality egg production in female channel catfish. A 10 week feed trial was conducted in ponds in Auburn, Alabama. In March, 219 female channel catfish brood stock were stocked into nine ponds 0.04 ha in size each for an approximate stocking rate of 1,332 kg/ha. Three dietary treatments were randomly allocated to the fish. Diet-1 was a standard 32% crude protein, 6% lipid floating catfish feed. Diet-2 was the same feed supplemented with forage fish at approximately 28 kg/ha. The third diet was the aforementioned catfish feed top-coated with 2% lipid (1% Menhaden fish oil, 0.5% high DHA oil and 0.5% high ARA oil). The fish were fed the prepared feeds three times a week at 1.5% body weight per feeding. Dissolved oxygen and temperatures were measured twice daily at dawn and dusk, and low DO events were mitigated by nighttime aeration. Ammonia, nitrite and pH parameters were measured twice a week. In May, the females were harvested, administered injections of luteinizing hormone releasing hormone analog to induce ovulation and strip spawned. The eggs were fertilized with blue catfish sperm and incubated in paddle wheel troughs. Percent viable fry was estimated by egg mass assessments 24 hours prior to hatch and resultant fry counts. The spawning data indicates brood fish fed the high lipid diet spawned larger egg masses (+17.6 g eggs/kg brood fish, p=0.003) and had larger eggs both in weight and diameter, when compared to either the control or forage fish treatment (+2.5mg and +0.3mm, p=0.001). These eggs, in turn, had increased complements of high quality lipids such as DHA, EPA and total n-3 fatty acids (p=0.001).