INFLUENCE OF TRANSITIONING TO DRY DIETS ON GROWTH AND POTENTIAL IMPLICATIONS ON RATE OF DEFORMITIES IN BIGHEAD CARP Hypophthalmichthys nobilis

Two experiments were conducted to evaluate how bighead carp juveniles transition to dry diets after larval rearing with live feeds and potential impacts of diet on growth, survival, and deformities .

The first experiment followed a larval density experiment (12.5, 25, 50 fish L^-1) where two live feed regimes were examined and 30 fish from each initial density and feed regime, in triplicate, were transitioned to a  commercial  dry diet for 11 weeks. Samples were taken to measure growth, feed coefficient ratio, and deformities. Deformities were classified in two categories, slight  (cataracts in or missing one eye, and minor spinal, jaw, and operculum deformities) and severe (cataracts in or missing both eyes, easily noticeable dorsal uplift of the caudal peduncle or curvature  of the  spinal  column and severe jaw deformities) . N o significant effect of initial stocking density or initial feed on survival (97 ± 2%, mean ± SD), growth (4.9 ± 1.3 g)  the rate of deformities was identified . P roportion of non-deformed (0.62 ± 0.13), slightly-deformed (0.27 ± 0.10), and severely-deformed fish (0.11 ± 0.08) were found.  Samples of both non- deformed and deformed fish, from similar history, were taken to measure whole body mineral content.  While there were some general trends observed, such as lower total ash and phosphorus content in deformed than non-deformed fish, no significant differences were found in mineral contents. The rate of deformities was rather high in the experiment, but these levels are not previously unseen in the culture of other carp species.

The second experiment occurred the following year and was conducted to examine whether the initial  commercial  dry diet impacted the rate of deformities. Following a similar live feeding period of 20d, the rate of observed deformities was 7 ± 2%. Fish were stocked (n = 38) to 10L tanks and three diets were tested, in triplicate. T he same commercial diet as the first experiment, as well as 2 formulated diets with either 50% of the protein source being from soybean meal or spirulina powder. The experiment is currently on going, but will follow a similar design to the first experiment, with growth, feed coefficient ratio, deformities observed and whole-body mineral analysis of the fish from each diet group being examined. Fish will be grown to a similar  size before being sampled for mineral analysis due to large differences apparent in growth rates between the commercial and formulated diets (Table 1)