Parental contribution and spawning performance in captive common snook Centropomus undecimalis broodstock

Common snook are a species relatively new to aquaculture and to date, virtually no information is available on captive broodstock spawning characteristics. Understanding basic and fundamental data such as broodstock contribution of captive mass spawning snook is important, not only for the development of a successful selective breeding program for the species, but also for restocking wild fisheries and maintenance of local genetic variation. A scoping study was undertaken to explore the potential of DNA profiling for monitoring mating outcomes in captive snook. Spawning success was monitored among wild harvested broodstock that were undergoing hormonal treatment to induce spawning. The broodstock were maintained in three separate tanks (Tank A: 18 males and 15 females; Tank B: 22 males and 11 females; Tank C: 40 males and 16 females) and were subject to different handling stresses. Sixteen mass spawning events were studied across the three tanks over a 15month period. DNA profiling of eight microsatellite markers was employed to detect and quantify individual parental contributions for 2,154 larvae obtained from the three tanks. The panel of loci was generally robust and allowed unambiguous assignment of 89% of larvae to a single family. All spawns occurred within approximately 24 to 72hours post-implantation and only females implanted with gonadotropin releasing hormone analogue (GnRHa) were found to contribute. Overall, spawning performance among the three tanks was highly variable in terms of the total number of eggs produced (from 86,300 to 2,378,000 per spawn), fertilization success (from 17.0 to 87.3%) and hatch rate (from 47.8 to 98.1%). Three-day larval survival ranged from approximately 25.9 to 90.1% in tank A and 19.9 to 74.2% in tank C. During this study, new information regarding requirements for broodstock husbandry, mating patterns and spawning periodicity of captive common snook broodstock were obtained. Spawn contribution data 1) provided a confirmation of GnRHa treatment efficacy in female snook with a minimum stage of oogenesis (late secondary growth-SGl) required for successful spawning; 2) identified a potential impact of handling on maturation and spawning in male and female broodstock; 3) confirmed that, through photothermal conditioning, captive common snook broodstock can spawn over consecutive days and several times per year, including outside of their natural spawning season.