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Title: Cannibalism in single-batch hybrid catfish production ponds

Author
item Torrans, Eugene
item Ott, Brian

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 8/11/2015
Publication Date: 2/19/2016
Citation: Torrans, E.L., Ott, B.D. 2016. Cannibalism in single-batch hybrid catfish production ponds. Aquaculture America Conference. P. 116.

Interpretive Summary:

Technical Abstract: Hybrid catfish are more efficiently harvested by seining than are Channel Catfish. Due to that, and their faster growth, hybrids are typically produced in “single-batch” production systems, either in intensively-aerated commercial ponds or in split-pond systems. In either production system, hybrids are typically harvested by seining twice in the fall or winter, and then to conserve water the ponds are typically restocked without draining. However, even with a skilled seining crew, 2-3% of the food-size hybrids may be missed after two seine hauls. There is concern among some catfish farmers that without completely draining or poisoning the pond after harvest, enough food-size hybrids (so-called “carry-over” fish) may remain that cannibalism by those larger fish may result in significant mortality of the smaller understocked fingerlings. The purpose of this study was to determine if small hybrid fingerlings stocked after the fall harvest would be eaten by the carry-over fish over winter. Six 0.04 ha ponds at the USDA ARS Warmwater Aquaculture Research Unit pond facility at Stoneville, Mississippi were used in this study. Three ponds were each stocked on November 25, 2013 with 100 (2500/ha) 11/2-year-old hybrid catfish averaging 1.07 kg (2.36 lbs). These fish simulated carry-over food fish from a single-batch production system that were missed after seining at the end of the growing season. All six ponds were then stocked on November 27, 2013 with 300 hybrid catfish fingerlings (7500/ha) averaging 14.8 g (32.5 lbs/100). The fish were not fed overwinter. On March 26, 2014 the ponds were harvested by seining twice and then draining with the remaining fish hand-picked from the pond bottom. Large fish were counted and weighed in 15-fish batches; the fingerlings were euthanized in a MS-222 solution, counted and measured individually for total length and weight. No dead fish were observed during the study. Of the 300 large fish stocked in total, all but one survived over-winter (99.7% survival). Although they were not fed, weight loss by these large fish averaged only 1% in the four months of the study. Weight gain of the fingerlings averaged 15.2% overall and was not significantly different among treatments. Survival of the understocked fingerlings was not significantly different (P=0.674) among treatments, averaging 91.9% and 92.9% in the ponds with and without carry-over fish (Table 1). The difference in fingerling survival was neither statistically nor biologically significant, even though we stocked fingerlings that were smaller than are typically used by the industry, and used more carry-over fish than are normally seen to exaggerate any effect. This study indicates that there is no risk of cannibalism from carry-over fish on understocked fingerlings overwinter. The study was repeated during the following growing season do determine if there was a seasonal effect. That data will also be presented.