The purpose of this study was to determine the effects of supplemental feeding with forage fish on the spawning success and egg quality of channel catfish Ictalurus punctatus. Channel catfish broodstock were maintained for 2 years on a diet of either commercial catfish feed with 32% protein or commercial catfish feed and live blue tilapia. Fish fed forage fish had significantly larger eggs and a higher gonadosomatic index prior to the second spawning season. They also spawned larger eggs, had a higher hatch rate, and produced more and larger fry than fish fed only commercial feed. During the second year of the study, growth rates and food conversion ratios were better over the winter months for channel catfish fed supplemental forage but worse over the summer months compared with fish fed only commercial feed. Over the two spawning seasons, broodstock fed forage fish produced an average of 9,221 sac fry/kg of females stocked in the spawning ponds. The addition of 10-15 kg/ha of blue tilapia to channel catfish broodstock ponds in the summer appears to be a practical method of increasing spawning success and fry production.
Mibolerone (MI), a synthetic steroid, was used to sex‐reverse undifferentiated Oreochromis aureus fry. Fry were exposed to 0.0, 0.3, 0.6, or 1.0 ppm MI in static‐water solutions for five weeks (immersion treatments) or were fed a diet containing 1.0 ppm MI for four weeks in a flow‐through system. Following hormone treatment, the fish were grown to over 60 mm total length prior to sex determination using gonadal squash examination. Fish immersed in 1.0, 0.6, or 0.3 ppm MI had average tissue MI concentrations of 14.4, 5.6, and 3.3 ppm, respectively. Immersion in either 1.0 or 0.6 ppm MI for five weeks resulted in an average of 82% males and 18% ovo‐testicular fish (inter‐sex fish) with no gonadal females being produced. Exposure to 0.3 ppm MI resulted in 78.7% males, 20.7% ovo‐testicular fish, and 0.7% gonadal females. Feeding a diet containing 1.0 ppm MI resulted in 85% males, 11% ovo‐testicular fish, and 4% gonadal females. Fry growth and survival were negatively correlated with the MI concentration of the immersion treatments. Exposing tilapia fry to static‐water solutions of 0.6 ppm MI for five weeks appears to be a feasible method of eliminating the production of functional females. Immersion solutions should be changed at least weekly to maintain an effective hormone concentration.
Mibolerone (MI), a synthetic steroid, was used to sex‐reverse undifferentiated Oreochromis aureus fry. Fry were exposed to 0.0, 0.3, 0.6, or 1.0 ppm MI in static‐water solutions for five weeks (immersion treatments) or were fed a diet containing 1.0 ppm MI for four weeks in a flow‐through system. Following hormone treatment, the fish were grown to over 60 mm total length prior to sex determination using gonadal squash examination. Fish immersed in 1.0, 0.6, or 0.3 ppm MI had average tissue MI concentrations of 14.4, 5.6, and 3.3 ppm, respectively. Immersion in either 1.0 or 0.6 ppm MI for five weeks resulted in an average of 82% males and 18% ovo‐testicular fish (inter‐sex fish) with no gonadal females being produced. Exposure to 0.3 ppm MI resulted in 78.7% males, 20.7% ovo‐testicular fish, and 0.7% gonadal females. Feeding a diet containing 1.0 ppm MI resulted in 85% males, 11% ovo‐testicular fish, and 4% gonadal females. Fry growth and survival were negatively correlated with the MI concentration of the immersion treatments. Exposing tilapia fry to static‐water solutions of 0.6 ppm MI for five weeks appears to be a feasible method of eliminating the production of functional females. Immersion solutions should be changed at least weekly to maintain an effective hormone concentration.
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