Disease Resistance Of Different Genetic Types Of Channel Catfish, Ictalurus Punctatus, Female×Blue Catfish, I. Furcatus, Male Hybrid Catfish

Catfish industry is playing a very important role in the US aquaculture industry. In 2015, catfish production constituted more than half of the total domestic freshwater production in the US. Among a lot of catfish species, channel catfish and hybrid catfish are used most widely in catfish farms due to their superior traits, such as faster growth and higher production. Thus, there are extraordinarily considerable economic value and vast prospect of commercial application on the research of catfish. However, with the improvement of intensive aquaculture and the expansion of catfish culture, the US catfish industry has suffered the biggest ever challenge. Outbreaks of catfish diseases become the leading cause of recession of catfish production in consecutive years. Columnaris and ESC(Enteric Septicemia of Catfish) are the most common cases in the catfish disease reports. Although these two diseases were first reported and even their pathogens were isolated decades ago, the pathogenic mechanisms and treatments of high efficacy are still being explored. Therefore, this study compared the disease resistance of different genetic types of hybrid catfish and channel catfish against columnaris and ESC. It can lay the foundation for further genetic improvement to enhance the disease resistance of catfish, improve the issues of frequent disease outbreaks and stimulate the development of catfish industry consequently. The outlines of this study are summarized as follows:Eleven genetic types, Kansas Random × Rio Grande, Kansas Select × Rio Grande, 103 KS × Rio Grande, Marion Select × Rio Grande, 103 KS × B, Marion Select × B, Auburn-Rio Grande × B, 103 KS × D&B, Kansas Random × D&B, Marion Random × D&B, and Kansas Select × D&B, of channel catfish, Ictalurus punctatus, female × blue catfish, I.furcatus, male hybrid catfish were challenged with virulent Flavobacterium columnare in tanks. Sex and the interaction between sex and genotype did not affect the disease resistance. The genetic type was the key factor associated with columnaris resistance of hybrid catfish. There was no apparent sire effect, but there was a significant(P<0.05) dam effect on mortality, median death time and average survival times. 103 KS had the best combining ability to produce hybrids with the best columnaris resistance. The best strategy to improve disease resistance of hybrid catfish is to identify female strains with the best combining ability. Potential genetics of these dam effects requires further study.Two genetic types of hybrids and one genetic type of channel catfish performed similarly in regards to mortality and survival time when challenged with Edwardsiella ictaluri, causative agent of enteric septicemia of catfish(ESC). However, the channel catfish had the largest death rate. The experiment was complicated by co-infections with both ESC and Ichthyophthirius multifiliis(Ich). The mortality and survival time of the two types of ich infected hybrid catfish were similar, while the death rate and extent of death for the channel catfish were the highest. The difference in ESC resistance of the hybrid catfish and channel catfish were not as great as seen in earlier experiments. This may be a result of genotype-environment interactions from the intensity of the infection or the multiple infections. Additionally, the channel catfish used in this study was an intraspecific crossbred in channel catfish and may have improved disease resistance compared to channel catfish in previous comparisons. Intraspecific crossbreeding may be an alternative to interspecific hybridization for enhancement of disease resistance and should be further explored.