Reducing operational costs and avoiding transmission of diseases continue to be critical areas of study in aquaculture. Two experiments were designed to address these issues. The first experiment examined a major cost associated with sunshine bass (Morone chrysops x M. saxatilis) production, feeding. The effects of four diets on the survival, growth, and body composition of sunshine bass were examined in a feeding experiment, followed by a fasting period. The diets consisted of a high nutrient commercial diet, a practical diet (wheat gluten based), a semi-purified diet (standard nutrient requirements), and a frozen natural diet. Fish were fed by hand three times a day at a rate of 4% of their body weight for 51 days. Survival was significantly lower for fish fed the semi-purified diet. Maximum growth was found in fish fed the commercial diet. To our knowledge, no previous studies with sunshine bass conducted a fasting experiment (14 days) aimed at replicating the conditions of transport and acclimation of farmed fish to new environments. Body composition was significantly affected by diet, and protein depleted faster than lipid during the fasting period. Analysis suggests that sunshine bass utilized protein and glycogen prior to lipid during fasting. At the end of fasting, samples of juveniles were collected for histological analysis of the liver and posterior intestine. The liver contained hepatocytes with larger deposits of lipids and nucleus pushed to the cell wall in fish fed the AN diet than the fish fed the FC diet. The posterior intestine revealed significant differences in the height of folds and number of goblet cells.
The second experiment was designed to eliminate the transmission of pathogens, specifically viral hemorrhagic septicemia (VHS), in hatchery operations. Avoiding viral disease transmission is vital for sport fish hatchery-based stocking programs in regions affected by VHS. Iodine compounds are nonselective antiviral substances that have been used widely as disinfectants, but their effects on embryo survival and early ontogeny of fish are less known. Two groups of walleye (Sander vitreus) were collected from the Maumee River, Perrysburg, Ohio in March 2009. Gametes were collected on site, and transported to the aquaculture laboratory in the School of Environment and Natural Resources, The Ohio State University. Eggs from each individual female were fertilized with the combined sperm of 3-4 males. Following fertilization, a tannic acid treatment for egg de-adhesion was used. Then embryos were exposed to iodine at 0 (control) or 100 mgL-1 (in triplicate) for 30 min., and incubated in California trays at 10-12 °C. Survival was estimated at the eyed-stage. Larvae were sampled prior to first feeding at 9 days post hatch (DPH) and approximately every 10 days until 48 DPH to assess growth. The results suggest that embryo survival following iodine treatment appears to be affected by the condition of the parents, but the growth of embryos was unaffected by the treatment. Histological analysis of larval swim bladder morphology revealed that non-inflated swim bladders had features of an underdeveloped organ with hyperplastic epithelium and vacuolarized cells.