Suppression of Cannibalism during Larviculture of Burbot through Size Grading

Abstract

The survival and percentage of North American Burbot Lota lota maculosa larvae and metamorphosing larvae presumed to have been cannibalized during a 15-d period immediately following a size-grading event were compared with those of fish in nongraded control groups. In larvae (mean TL, 11.8 mm), grading immediately produced a size distinction, as the group that passed the grader was significantly narrower and shorter than the group retained by the grader. The mean coefficient of variation of the length of larvae in the retained group was significantly lower than that of the control group, indicating that grading reduced size heterogeneity. Grading significantly increased larval survival, which averaged 74.3% and 93.3% for the passed and retained fish, respectively, compared with 59.3% in the control. Increased survival was linked to a reduction in the percentage of larvae presumed cannibalized in the graded groups. In metamorphosing larvae (mean TL, 21.0 mm), grading did not significantly change TL, width, or the coefficient of variation of length, nor did it improve survival or reduce presumed cannibalism. This study provides initial empirical evidence that size grading can be an effective way to significantly reduce cannibalism when done at the onset of cannibalism in larval-stage Burbot.

Received May 15, 2013; accepted July 22, 2013

ACKNOWLEDGMENTS

This project was funded in part by the U.S. Fish and Wildlife Service (grant 14330-7-H067). Special thanks to Ray Jones for program funding and coordinating. This project was also supported by the Kootenai Tribe of Idaho and the Bonneville Power Administration (project 198806400; contract 46821). We extend our deepest gratitude to the Kootenai Tribe of Idaho, the British Columbia Ministry of Forests, Lands, and Natural Resource Operations, the Idaho Department of Fish and Game, Cramer Fish Sciences, the U.S. Fish and Wildlife Service, and the University of Idaho Aquaculture Research Institute (UI–ARI). We extend our gratitude to Susan Ireland of the Kootenai Tribe of Idaho for her support and dedication. Without these collaborators this work would not have been possible. Finally, we thank the UI–ARI staff members who assisted during this study. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.