Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 2004
Publication Date: October 1, 2004
Citation: Green, B.W., Heikes, D., Goodwin, A.E. 2004. Comparison of three grading channel catfish stockers. North American Journal of Aquaculture. 66:251-260.
Interpretive Summary: Separating channel catfish into defined size groups before stocking in grow out ponds reduces size variation in the fish population through harvest, reduces the number of sub-marketable fish at harvest, and improves ability to census the fish population accurately. Separating fish by size is called grading, and can be accomplished with mechanical graders or passive graders. This experiment evaluated performance of the recently developed UAPB in-pond mechanical grader compared to a box grader (mechanical) and in-pond grading net (passive) at separating a catfish population into distinct size classes.
Each grader separated the initial catfish population into distinct size groups. Fish condition affected the grading process: because the fish used in this experiment were thin, the sizes at which the population was split into groups was shifted to higher size classes. A population of medium size fish was obtained with both the box and UAPB graders. However, average individual weight and length of medium size fish was smaller in the population selected by the UAPB grader. This means the bar spacing on the UAPB grader must be set slightly wider if the goal is to obtain a fish population similar to the box grader. The grading error was similar for both the box and UAPB graders. Large fish were graded successfully from the initial population with each grader, but fish selected with the grading net were smaller than those selected with the box or UAPB graders.
This experiment demonstrated the importance of evaluating fish condition when grading fish by size. Also, mechanical graders allow separation of fish populations into distinct size groups more quickly than passive graders. This should allow for savings in labor costs associated with grading.
Stocking size-graded catfish into productions ponds is beneficial. This study evaluated the effectiveness of the recently developed mechanical grader, denoted the UAPB in-pond mechanical grader, compared to box and sock graders, and assessed injuries sustained during grading a population of stocker channel catfish Ictalurus punctatus. Three 0.25-acre ponds were stocked at 11,777 lb/acre. Initial population individual total length (TL) and weight ranged from 16.3-15.7 in/fish and 0.04-1.10 lb/fish, respectively. The fish population in each pond was divided into three groups and graded with the box, UAPB, or sock grader. Fish were graded twice with the box and UAPB grader; a bar spacing of 1-3/32 inch was used to grade off small fish, and 1-3/8 in to grade off large fish. Sock grader mesh size was 1-3/8 inch. Fish populations were sampled prior to and following grading, and weighed and measured individually. Blood samples were collected from sampled fish and serum analyzed for creatine kinase and lactate dehydrogenase. Each grader separated the initial population into distinct populations. Fish used in this experiment were thin, which resulted in grading split points being shifted to higher size classes. Mean individual weight and total length of medium size-class fish was significantly lower for the UAPB grader compared to the box grader. The frequency distributions of the graded fish populations obtained with each grader differed significantly from one another. Undergrade and overgrade error for the medium size-class population did not differ significantly between the box and UAPB graders and averaged, respectively, 5.4% and 7.8% for TL, and 1.6% and 10.3% for individual weight. Serum creatine kinase and lactate dehydrogenase activities were highly variability, which prevented detection of significant treatment differences.