Seasonal variations in gametogenesis and gross biochemical composition of the tissues of the pen shell Atrina pectinata in a temperate coastal bay of Korea

Abstract

Seasonal variations in the condition, gross biochemical composition, and reproductive activity of bottom cultured pen shell Atrina pectinata were studied over a period of 13 months from July 2010 to July 2011. Separate analyses were made of adductor muscle, gametes and the remaining tissues for monthly collected individuals. The condition and gonadosomatic indices (CI and GSI) of the pen shell peaked in spring and were followed by a sudden decline in summer. Dry weight, gross biochemical composition, and energy content of whole tissues of a standard animal (dry shell weight = 113.6 g) showed a similar seasonal cycle to those of CI and GSI. The gonadal tissues of the pen shell initiated growth simultaneously with the weight (also protein and carbohydrate) gain of the adductor muscle during the spring period, indicating its opportunistic reproductive strategy by which gametogenesis occurs at the expense of immediately ingested food energy. During the spring growth period, the energy reserves were stored in the forms of proteins and carbohydrates (mainly glycogen) in the adductor muscle. Although energy reserves increased in the form of proteins and lipids in the gonad during that time, a complete exhaustion of these reserves during the summer spawning indicated that proteins and lipids in the gonad are major constituents of gametes. In contrast, rapid consumption of proteins and glycogen in the adductor muscle during spawning suggests that these reserves are used as catabolic substrates during spawning. Inter-annual difference in the spawning period of the pen shell was likely to be related to the energy storage and gamete growth in each spring. Finally, our results suggest that separate biochemical analyses of various organs can provide more realistic information on the processes of energy gain and mobilization of bivalves and, in the case of the pen shell, the adductor muscle plays a critical role as major organ related to energy storage-utilization.