Comparison of three methods of size grading channel catfish stockers

The stocking of size-graded catfish into production ponds should increase production efficiency, but grading large numbers of fish with existing technology is laborious. We evaluated the effectiveness of a mechanical grader recently developed at the University of Arkansas at Pine Bluff (UAPB) relative to that of box and sock graders and assessed injuries sustained by stocker channel catfish Ictalurus punctatus during grading. Three 0.25-acre ponds were stocked at 11,777 lb/acre. Initial total length (TL) ranged from 6.3 to 15.7 in, and initial weight of individuals ranged from 0.04 to 1.10 lb. The fish population in each pond was divided into three groups graded with the box grader, UAPB grader, or sock grader. Fish were graded twice with the box and UAPB graders; a bar spacing of 1(3)/(32) in was used to grade off small fish and a spacing of 1(3)/(8) in to grade off large fish. Sock grader mesh size was 1(3)/(8) in. Mean weights and lengths of the size-classes produced by grading (small, medium, and large) were compared to those of the initial population in each pond. Blood samples were collected from sampled fish, and serum was analyzed for creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) activities to assess fish injury levels. Each grader separated the initial population into distinct populations. Mean weight and TL of the medium size-class was significantly lower for the UAPB grader than for the box grader. The frequency distributions of the fish populations obtained from each grader differed significantly. Undergrade and overgrade error for the medium size-class did not differ significantly between the box and UAPB graders. Undergrade error averaged 5.4% for TL and 1.6% for individual weight; overgrade error averaged 7.8% for TL and 10.3% for weight. Serum CPK and LDH activities were highly variable, which prevented detection of significant treatment differences.
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