Size-dependent spawning and egg quality of Red Snapper: Final Progress Report Submitted to MARFIN
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Size-dependent spawning and egg quality of Red Snapper: Final Progress Report Submitted to MARFIN

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  • Alternative Title:
    Final Progress Report Submitted to MARFIN
  • Description:
    The project goal was to study the reproductive biology of red snapper in the laboratory emphasizing the size-specific spawning potential and the quality of female spawns. The objective was to determine the size-specific potential of young female red snapper to contribute to the spawning stock. Adult red snapper ranging in size from 305-579 mm TL (12.5-25 in.) for females and 298-521 mm TL (11.75-20.5 in.) for males were captured by hook and line at weekly intervals during a period from the end of May through the middle of October. Fish were brought to the lab in a transport tank, held overnight then sexed by catheterization. Individual females were injected with HCG (Human Chorionic Gonadotropin; 1.1 IU per gram body weight) and paired with two ripe males injected with HCG (0.55 IU per gram). Fish were held at field temperatures and photo period in spawning tanks for up to 3 days or until they spawned. Spawned eggs were counted and a subsample measured. Spawning in the laboratory took place between,2300 and 0100 hours typically 30-36 hours after injection. Laboratory spawnability of red snapper was highest in June, July and August and decreased in September and October. Overall laboratory spawnability for age 2 fish was low (-20%) and increased significantly in older females (-70%). Batch fecundities ranged from several hundred eggs for a 317 mm, age 2 female to 255,000 for a 552 mm age 5 snapper. There were no discernible differences in egg diameter related to female size or age. Mean egg diameters ranged from 0.71 to 0.81 mm with an overall mean of 0.77 mm and showed no obvious size-dependent or seasonal trends when all size classes were plotted together. However, when spawns from age 3 fish were plotted by month a trend of declining egg size later in the spawning season was apparent. Based on results from this study it is reasonable to conclude that while some age 2 female red snapper are spawnable, age 2 fish are unlikely to contribute significantly to spawning stock biomass. Numerous age 2 (25%) and age 3 (33%) males with flowing sperm were captured, one as small as 298 mm TL (11.75 in.), suggesting that age 2 males may participate in spawning at a higher frequency than females.
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