WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2012 29 was placed in each pond and activated when dissolved oxygen concentration fell below 5 mg/L. All fish were harvested in late September, 2010. There was little difference in growth among the hybrids and bluegill, except for the warmouth × bluegill hybrid, which were much smaller than fish of other crosses (Fig. 5). Fish feed represents over half the cost of raising fish and unfortunately this expense has been increasing dramatically the past few years, mostly due to rapid increases in commodity grain prices. Making a profit is related directly to how efficiently the fish use feed and how efficient the fish culturist is in feeding the fish. Because different species or crosses were stocked together, it was not possible to calculate conversion rates for each cross, but we determined the conversion rates for the aggregate group of hybrid sunfish in each pond (Fig. 6). All feed conversion ratios were less than two, indicating that feeding efficiencies were acceptable. Sources of Mortality Fish were lost to predators such as fish-eating birds, otters, and turtles. Sunfish are especially vulnerable to predators because of their relatively small size and tendency to remain in shallow water, especially at night. In the study comparing hybrids, survival ranged from 71 to 80 percent. Mortalities are not always observed by the fish culturist and may result in overfeeding. Careful hand feeding can minimize over or under feeding because the feeder can determine when fish activity stops. Hybrid Sunfish Dress-Out Sunfish dress-out percentage is important because the bottom line of price and revenue are directly affected. For example, if average dress-out is 35 percent and the cost to raise sunfish is $0.91/kg, then the cost to produce fillets is $2.60/ kg ($0.91/0.35=$2.60/kg). This cost does not include processing expenses. Harvested fish were dressed; half were filleted and half were scaled, gutted, and the head removed, which is considered “in the round” processing. There was little difference in dress-out among the crosses (Fig. 7) and there was very little difference among crosses in fillet yield relative to fish size. Although fillets are often in greater demand than fish in the round, producers may market dressed fish to enhance profitability. Yield of fish in the round is greater and processing costs are less. All three hybrids performed (CONTINUED ON PAGE 28) Your research is unique. Your aquatic housing system should be, as well. Aquatic Enterprises Inc. specializes in the design, engineering and in-house manufacturing of custom fresh and saltwater research aquariums and rack systems. The result is an innovative aquatic system that optimizes your research. To find out more about how affordable a custom Aquatic Enterprise system can be, contact us at 206.937.0392 or info@aquaticenterprises.com www.AquaticEnterprises.com biofilters with about 1 m3 of bio-balls, and a rotating drum filter for solids removal. Each tank received water at a rate to provide a complete change every 30 minutes. Equal numbers of each hybrid cross and bluegill were stocked in each tank and there were six replicates of each cross. Fish were maintained on a 16-h light and 8-h dark cycle. Fish were fed daily using a belt feeder. Feeding rate was adjusted by observing feeding behavior of fish and estimating the amount of feed remaining in a tank each morning. When the indoor test was terminated, each fish was weighed and measured (Fig. 4). The weight of bluegill was 23 percent greater than that of the green sunfish hybrid, 29 percent greater than that of the redear hybrid, and 47 percent greater than that of the warmouth hybrid. Second-Year Pond Phase The study continued through the second-year pond grow-out phase. In April, about 256 of each cross were stocked in each of four 100-m2 ponds. Feed was placed into feeding rings twice daily (early morning and late afternoon) and the same ration was used through the summer. Dissolved oxygen, water temperature, pH, ammonia, and nitrite did not exceed normal limits at any time during the pond evaluation. A ½-hp, vertical pump aerator
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