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Title: No evidence for intercohort cannibalism in mixed-size cultures of food-size and fingerling hybrid catfish (channel catfish x blue catfish) grown in ponds in winter or summer

Author
item Torrans, Eugene
item Ott, Brian

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2015
Publication Date: 12/21/2015
Citation: Torrans, E.L., Ott, B.D. 2015. No evidence for intercohort cannibalism in mixed-size cultures of food-size and fingerling hybrid catfish (channel catfish x blue catfish) grown in ponds in winter or summer. North American Journal of Aquaculture. 78(1):52-56.

Interpretive Summary: Hybrid catfish (a cross between channel and blue catfish) are harvested by seining and the ponds are typically restocked without draining. A few food-size fish usually escape seining and are left in the pond. Farmers are concerned that these larger fish may eat (“cannibalize”) the smaller fingerlings when they are stocked after the fall harvest. This study examined the cannibalism of smaller fingerlings in both winter and the following growing season. Results show that fingerling survival was similar in ponds with and without larger fish. While those larger fish may grow too large for the processor’s prime fish size range during the next growing season, bringing a discounted price, and will convert feed poorer, the risk of cannibalism is not a concern.

Technical Abstract: Hybrid catfish (' Channel Catfish Ictalurus punctatus X ' Blue Catfish I. furcatus) are normally harvested by seining single-batch pond production systems in fall or winter. Ponds are typically restocked without draining. There is concern that without completely draining the pond after harvest, food-size hybrids that escape seining may cannibalize 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 larger fish over winter or during the following growing season. Three 0.04 ha ponds were each stocked on November 25, 2013, with 100 1.5-year-old hybrid catfish averaging 1.07 kg. Those three ponds and an additional three ponds were then stocked on November 27, 2013, with 300 hybrid catfish fingerlings averaging 14.8 g. The fish were not fed over winter. On March 26, 2014, the ponds were harvested and all fish were counted and weighed. Survival of the large fish was 99.7%. Survival of the understocked fingerlings was not significantly different between treatments, averaging 91.9% and 92.9% in ponds with and without large fish. On April 9, 2014, four 0.04 ha ponds were each stocked with 40 hybrid catfish averaging 1.12 kg. Those four ponds and an additional four ponds were then each stocked with 800 hybrid catfish fingerlings averaging 23.6 g on April 23, 2014. The fish were fed through the growing season and harvested on October 7-10, 2014. Survival of the large fish was 99.4%. Survival of the small fish was not significantly different between treatments, averaging 88.8% and 90.3% in ponds with and without large fish. This study indicates that cannibalism from carry-over fish does not have a significant impact on understocked fingerling survival either over-winter or during the following growing season.