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Abstract
Hybrid catfish (female channel catfish Ictalurus punctatus × male blue catfish I. furcatus) can be obtained by induced spawning and artificial fertilization; the results, however, are variable. A threshold degree of maturity must be reached before broodfish can be induced to spawn, but selection of such fish can be very subjective. In the present study, female brood channel catfish were classified subjectively as poor, fair, or good as well as on the basis of body weight, total body length, body width and girth, and the ratios of these measurements. Brood females were held at 24, 26, and 28°C in 100-L aquaria and injected with synthetic analogues of luteinizing hormone releasing hormone at 20 μg/kg, followed 12 h later by an additional injection of 100 μg/kg. Data were collected regarding spawning success, time to egg release following injection, fecundity, egg diameter, hatching, and survival rates. For the population as a whole at all three temperatures the spawning rate was 73.8%, but among females that met certain selection criteria greater spawning rates occurred. Females with a length: body width value of less than 5.5 had a spawning rate of 88.9%, and those subjectively classified as good had a spawning rate of 85.7%. The temperature at which broodstock were held affected the spawning rate; females classified as fair and good had spawning rates of 52.9, 82.4, and 95.5% at 24, 26, and 28°C, respectively. Females classified as good spawned earlier than lesser-quality fish. Likewise, females with length: girth values of 1.8 or less or length: width values of 5.0 or less spawned sooner than females with higher values. Brood selection criteria also resulted in selected subsets with greater fecundities, larger egg diameters, and, in some cases, an overall greater production of swim-up fry per kilogram of female.
Received August 13, 2010; accepted October 11, 2010
