Seasonal changes in the reproductive condition and body composition of free-ranging red drum, Sciaenops ocellatus

Abstract

Adult red drum ( Sciaenops ocellatus) from a wild, autumn (fall) spawning population were studied over a 1-year period to evaluate seasonal changes in body composition in comparison with cultured red drum. Each month, female and male fish were captured and blood sampled. Standard length and weight were measured, and gonads, liver, intraperitoneal fat (IPF), and a sample of muscle tissue were collected from each fish. Gonadosomatic index (GSI), hepatosomatic index (HSI), IPF ratio, protein and lipid composition of muscle and liver tissues, and lipid class composition of liver samples were determined for each fish. All tissue indices exhibited a similar seasonal cycle in both sexes, with highest HSI in spring (March–April) and maximal IPF ratio in May, followed in September and October by minimal values for HSI and IPF ratio. Whereas GSI was low, gonadal histology demonstrated activation of spermatogenesis and oocyte development in July and August. Liver composition varied dramatically throughout the year. Liver lipid content ranged from 7.4% of wet weight in November to 30.2% in August, with triglycerides (TG) being the most abundant component at all times. Liver protein was more stable, ranging from 11.5% in August to 16.3% in September. Muscle composition was relatively constant, with muscle crude protein ranging from 20.5% to 25.6% of wet weight and muscle lipid ranging from 0.4% to 2.2% of wet weight. These data indicate that red drum utilize the liver as a major depot for lipid. Depletion of maximal lipid reserves from liver and IPF in late summer indicates that lipid stored during active spring and summer feeding supplies energy for reproduction which is mobilized rapidly (within 1 month) in this fall-spawning species. Body composition of wild fish is similar to that of laboratory cultured red drum.