Largemouth bass (LMB) are an important recreational fish and are increasingly grown as a food fish. There is need for methods to consistently produce quantities of LMB fingerlings. Current practice to produce phase one LMB relies on dedicated nursery ponds filled on demand and harvested after several weeks. Managed nursery ponds are fertilized to promote natural food, primarily zooplankton and insect larvae. Fingerlings produced are then feed trained and graded to manage the risk of cannibalism.
Floating raceways represent a novel approach for phase one production of phase I LMB. Mesh size may be chosen to retain fish and possibly components of the bloom. The volume of water pumped through the raceway is directly related to the quantity of natural food presented to the fish. It offers convenient monitoring and ease of harvest. Multiple raceways with diverse age groups can be placed in a single managed pond.
Previous studies conducted at the Kentucky State University Aquaculture Research Center have demonstrated proof of concept. The system also produced smaller sized fingerlings in contrast to conventional pond rearing method. Thus, questions regarding whether sufficient food (density and diversity) are being delivered and how they differ between the pond and floating raceway were explored in this study.
Investigators used eight 0.04 ha ponds fertilized to enhance the spring zooplankton bloom and a fertilization protocol based on methods used at the A.E. Wood Hatchery in San Marcos TX. Fish were not confined in the control (pond) treatment. Treatment fish were confined in a 2.6 m3 growing area inside the raceway with water pumped from the pond. Each treatment was stocked with 6000 LMB swim up fry. Fish and zooplankton samples were collected on a weekly basis and fish were harvested after 35 days. Zooplankton samples were obtained from three sources (Raceway, Raceway pump, and Pond) and were analyzed for quantity and diversity to assess zooplankton community structure. Water quality parameters were monitored on a weekly basis.
Fish were recovered from both treatments. Average weight was 3.57±0.54 grams in the control treatment and 0.86±0.18 grams in the raceway treatment. This represents a respective specific growth rate of 20 and 16 % body weight/day. Mean weight was significantly higher in control treatment than in the raceway treatment (P-value 0.003). Mean recovery was 785±352 fish in the control treatment and 2234±886 fish in the raceway treatment. Recovery rate was highly variable in both treatments such that there were no significant differences between treatments (P-value 0.179). Zooplankton data will be presented at the meeting.