Genetic architecture of early life history traits for channel catfish, Ictalurus punctatus ♀ x blue catfish, I. furcatus ♂ hybrid production

Hybrid catfish, the progeny of channel catfish, Ictalurus punctatus, females x blue catfish, I. furcatus, males are in high demand by the aquaculture industry due to their superiority for pond culture. Unfortunately, fry production is a limiting factor due to lack of natural hybridization between the species and the necessity to sacrifice males for artificial fertilization. In this study, we used a quantitative genetic breeding design to assess genetic, environmental, and genotype by environment interactions to detail the genetic architecture of fitness during the "critical" early life history (ELH) stages. Males and females were crossed using a full-factorial design, creating 20 unique families. Offspring from each family were split into 2 temperature-controlled environments based on conditions that mimic early (26.6 degrees C) and late (32.2 degrees C) seasonal temperatures. Embryonic survival, hatch success, larval morphology, and deformities were quantified at hatch, mid-yolk sac transition, and swim-up stages of early development. Variation in early performance traits (calculated as variance components, VC) were partitioned to maternal/paternal effects as well as parental x environmental interactions, analyzed across and within temperatures. Embryonic survival ranged from 45 to 93% by 120 degrees-hours post-fertilization and was not impacted by temperature. Maternal effects were responsible for large amounts of variation (VC = 51%), and paternal effects also became apparent during later stages of embryonic development but in smaller quantities (VC = similar to 7%). Temperature significantly impacted hatch success, in which hatch decreased at 32.2 degrees C (from 40% to 32%). Therefore, we conclude that temperatures at the start of the spawning season yield higher hatch success. Maternal effects were highly significant (VC = 65%), and there were also significant paternal effects (VC = 12%) with wide family variation (ranging from 14 to 71%). The deformity rate increased from 3.6% at 26.6 degrees C to 6.0% at 32.2 degrees C, but variation was driven more by maternal effects rather than temperature. For morphology, fry reared at 32.2 degrees C had smaller body sizes at each developmental stage. Maternal variation across morphology traits ranged widely from 9 to 80% and was highest for maternal yolk. Paternal effects/interactions ranged from to 0-29%. Genetic x environmental interactions were also observed for morphology traits since values for VCs differed within each temperature. This information showed the importance of environmental effects, parentage, and their associated interactions, which by isolating indicators of male/female quality, can be used to develop parameters for broodstock selection. Results can also be applied to improve incubation conditions for hybrid catfish during the crucial ELH stages.