GENETIC EFFECTS AND COMBINING ABILITY FOR OVERSIZED AND UNDERSIZED CHANNEL CATFISH Ictalurus punctatus FEMALE X BLUE CATFISH I. furcatus MALE HYBRID CATFISH

Oversized hybrid catfish (channel catfish, Ictalurus punctatus, female X blue catfish, I. furcatus, male) have become a significant problem at harvest for food-sized fish in the catfish industry. Conversely, hybrid catfish fingerling producers complain concerning undersized fingerlings. The population distribution of hybrids from F1 crossbred channel catfish dams was more variable than that from pure-strain dams with the greatest percentage of large fingerlings that would likely grow into oversized food fish from these crossbred dams. The same phenomenon was observed for hybrid progeny from F1 blue catfish crossbred sires. The F1 crossbred sires and dams were also more likely to produce undersized hybrid progeny. This initial study indicates that the use of F1 crossbred blue catfish males or F1 crossbred channel catfish females greatly increases variation in fingerling hybrid progeny. There are multiple ways to analyze size variability. If alternative measures of size variability were used such as the coefficient of variation, vagaries of the calculation will result in the opposite, but incorrect conclusion regarding variability of the hybrid progeny from crossbred brood stock because of the large standard deviation.

When the combining abilities were calculated from pooled full-sib and half-sib families across all genetic groups, there was no significant specific or general combining ability for the extremely large hybrid fingerlings, indicating that selection for combining ability in the parent species would likely not alleviate the oversized hybrid food-fish problem. However, there was significant dam general combining ability for slightly larger hybrid fingerlings and undersized fingerlings, indicating selection of the appropriate dam would likely increase uniformity in hybrid fingerlings, positively impacting the hybrid fingerling industry, which could also lead to greater uniformity of hybrids in the food-fish industry. Significant combining abilities existed for all of the other economically relevant traits of hybrid catfish.