A temperature-dependent measure of the mitotic interval (TO) can help standardi/e chromosome manipulation in tish eggs. A tau unit (TO) is the duration in minutes of one mitotic cycle during synchronous embryonic cleavage. It is measured over a range of temperatures, and the resulting relationship of TO to temperature can be used to anticipiate developmental events that are affected by temperature. Optimum induction of chromosome manipulation requires development of a specific treatment of egg shocking for each species. Timing of shock is a critical variable, but pretreatment incubation temperature affects the rate of development and thus the optimum absolute time for shocking. Mitotic intervals (TO) are reliable indicators of developmental rates over normal temperatures for egg incubation, and thus can be used to estimate optimal times for chromosome manipulation. Mitotic intervals for paddletish Polyodon spathula and shovelnose sturgeon Scaphirhynchus platorynchus were estimated by averaging the duration of the second and third embryonic divisions (twocell to four-cell and four-cell to eight-cell stages). Mitotic intervals (TO) for paddletish ranged from 74 ± 2.8 min (mean ± SD) at 16 C to 52 ± 1.4 min at 20°C; T O for shovelnose sturgeon was 66 ± 2.5 min and 45 ± 1.1 min at these temperatures.
In livestock industries such as poultry and swine, an extract of the Yucca shidigera plant has shown promise in controlling ammonia buildup in production facilities. In three trials, effects of Y. shidigera extract on ammonia levels and fish growth in recirculating‐water aquaculture systems were evaluated. When added to in vitro ammonia solutions, extract concentrations of 0.043% and 0.43% caused a significant (P < 0.05) reduction in ammonia levels after 24 h. The 0.43% concentration also caused significantly (P < 0.05) lower levels of nitrite and higher levels of nitrate. Both concentrations were subsequently found to be toxic to juvenile channel catfish (Ictalurus punctatus). In a feeding trial, fish fed diets containing 1.1‐g/kg concentrations of Y. shidigera extract had decreased (P < 0.10) weight gain and increased feed conversion (P < 0.05) compared with fish fed control diet, but there were no significant differences (P > 0.05) in ammonia, nitrite, and dissolved oxygen levels. These results suggest that Y. shidigera could be evaluated as a preconditioning agent for water‐recirculating systems and biofillers but should not be used in direct contact with fish.
Distillers dried grains with solubles (DDGS) were evaluated as an ingredient in practical diets for pond culture of the freshwater prawn Macrobrachium rosenbergii. Juvenile prawns averaging 0.66 ± 0.47 g were stocked into nine 0.02 ha ponds at 19,760/ha. Three isonitrogenous diets (29% crude protein) containing 0, 20, or 40% DDGS were fed to shrimp in triplicate ponds. Average yield, survival, individual weight, and feed conversion did not differ significantly (P > 0.05) among treatments. When averaged over the three diets, results were: yield, 833 kg/ha; survival, 75%; individual weight, 57 B; and feed conversion, 3.1. It appears that DDGS is a suitable ingredient for use in practical diets for freshwater prawns at levels of up to 40% of the total formulation, when prawns are stocked at the densities used in this study.
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