Suppression of Cannibalism during Larviculture of Burbot through Size Grading

The survival and percentage of North American Burbot Lota lota maculosa larvae andmetamorphosing 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. Themean 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. Inmetamorphosing 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.