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1.
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.  相似文献   
2.
There is growing use of hybrid catfish (Ictalurus punctatus ♀ X Ictalurus furcatus ♂) in commercial aquaculture to utilize hybrid vigour to improve production A conjoined twin specimen found during the course of production studies by the United States Department of Agriculture Catfish Genetic Research Unit (USDA‐CGRU) was submitted to the Aquatic Research and Diagnostic Laboratory (ARDL). After preliminary inspection, it was transported to Mississippi State University, College of Veterinary Medicine for further evaluation. The specimen was examined using both computed radiography and computed tomography antemortem. Following humane euthanasia, the specimen was examined both grossly and histologically. Tissues from both fish were also submitted for genetic analysis to determine whether twins were derived from the same egg. This report records the presentation and examination of a pair of conjoined hybrid catfish (I. punctatus X Ictalurus furcatus).  相似文献   
3.
Twelve 0.4‐ha ponds were stocked with 10,000 hybrid catfish fingerlings in March 2015. Six ponds were partially harvested in August to remove fish larger than ～0.57 kg. All remaining fish were removed in October and November. Partial harvest of faster‐growing fish removed ～26% of the fish initially stocked; feeding rate (and therefore external nutrient loading) was reduced by about the same amount. However, reduced nutrient loading after partial fish harvest had no meaningful effects on water quality, phytoplankton biomass, phytoplankton and zooplankton community structure, or supplemental aeration. Lack of ecosystem change was caused by persistent internal recycling of nutrients added to the system before partial harvest and continued high (albeit reduced) external nutrient loading after partial harvest. Decisions to employ partial fish harvest to manage single‐cropped hybrid catfish ponds should be based on economic considerations and risk reduction rather than the expectation that fish biomass reduction will improve water quality.  相似文献   
4.
Abstract.— Induction of triploidy and tetraploidy in Nile tilapia, Oreochromis niloticus , was investigated by heat shock, cold shock, hydrostatic pressure, and/or chemicals (cytochalasin A, B, and D). Additionally, efficacy of combined protocols was determined. Heat shock 10 min after fertilization induced triploidy when incubation temperature was 24 C but not when incubation temperature was 31 C. Heat shock of 40–41 C at 4–6 min after fertilization was effective in inducing up to 100% triploidy with hatchability similar to controls. Cold shock at 13 C for 45 min five min after fertilization induced 85–100% triploids. Heat shock and multiple heat shocking were the most effective treatments for the induction of tetraploidy. Two heat treatments of 41 C applied at 65 and 80 min after fertilization for 5 min each produced approximately 80% tetraploidy in hatched fry. Immersion of fertilized eggs in cytochalasin A, B, or D at concentrations up to 10 μg/L applied at various times and durations was ineffective in inducing triploidy or tetraploidy.  相似文献   
5.
Feed‐based production of ictalurid catfish in ponds is the largest aquaculture sector in the USA. Feed has an oxygen demand, and increases carbon dioxide, ammonia nitrogen, and phosphate inputs to ponds. Major sources of oxygen in ponds are phytoplankton photosynthesis and mechanical aeration; the major sink for oxygen is respiration by fish and by microorganisms in the water column and sediment. Dissolved oxygen concentrations decline when respiration exceeds photosynthesis, and the most crucial time for low dissolved oxygen concentration is at night. Mechanical aeration is applied to avoid nighttime dissolved oxygen concentrations from falling below the critical level for catfish of 3 mg/L. Electrically powered paddlewheel aerators are used by most catfish producers. The oxygen‐transfer efficiency of these aerators is known, but calculations of aeration requirement from stocking and feeding rates are not reliable because of variation in phytoplankton abundance and in weather conditions. Dissolved oxygen concentrations must be monitored, and when measurements suggest that nighttime dissolved oxygen concentration will be unacceptably low, tractor‐powered emergency aerators must be operated to supplement dedicated aeration. Dissolved oxygen concentration also is important in hatcheries, and small aeration systems have been developed for hatchery application.  相似文献   
6.
This study was designed to determine the effect of ovarian fluid pH of stripped unfertilized channel catfish, Ictalurus punctatus, eggs on fertilization and hatch rate of channel catfish ♀ x blue catfish, Ictalurus furcatus♂, hybrid catfish eggs. A significant correlation was established between ovarian fluid pH of stripped channel catfish eggs and hybrid embryo hatch rate (R2 = 0.75, P = 0.01), suggesting ovarian fluid pH of stripped catfish eggs prior to fertilization can be predictive of the hatching success of hybrid catfish embryos. These data were used to categorize pH of stripped eggs: pH <7.0 as “low pH eggs,” pH 7.0–7.4 as “medium pH eggs,” or pH >7.4 as “high pH eggs” quality eggs. The range in percent hatch rate for these pH categories was <15%, 15–30%, and >30%, respectively. Higher calcium concentrations during incubation do not appear to improve hatching success of “low pH eggs.” The predictive model presented herein describes a quick method for evaluating stripped catfish eggs for hybrid fry production in catfish hatcheries.  相似文献   
7.
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.  相似文献   
8.
Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, to “superdosing” of 6‐phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4‐ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4‐ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond‐raised hybrid catfish and had no beneficial effects on water quality.  相似文献   
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