Influence of temperature on gonadal development of Ruditapes philippinarum (Adams and Reeve, 1850) with special reference to ingested food and energy balance

This study evaluated the influence of temperature on gonadal development in Ruditapes philippinarum under controlled dietary conditions, in order to distinguish between the effect of temperature alone and the associated effect of temperature on ingestion. The experiment was therefore divided into two groups: group L (at temperatures of 14 degrees C and 18 degrees C, with a daily ingestion rate of 470-550 mu g organic weight of phytoplankton per g clam live weight) and group H (at temperatures of 18 degrees C and 22 degrees C, with a daily ingestion rate of 1000-1100 mu g organic weight of phytoplankton per g clam live weight). Both ingestion and respiration rates were calculated for each of the diets and temperatures. Gonadal development of the different groups of clams was monitored over the 70-day experimental period by means of image analysis techniques and calculation of the soft tissue dry weight of a standard clam. Experimental results show that when the amount of food ingested is similar a difference of temperature between 14 degrees C and 18 degrees C, or between 18 degrees C and 22 degrees C, has no significant effect on the rate of gonadal development, the effect of temperature possibly being masked by the differences in the respective energy balances. When a higher temperature coincides with a higher ingestion rate, as is often the case with naturally-occurring populations of bivalves, then gonadal development is greater, and faster, at the higher temperature, although this is mainly due to the greater amount of food ingested. When, in experimental (or environmental) conditions, a high temperature (18 degrees C) is associated with a low ingestion rate, a situation of negative energy balance arises, associated with a slow rate of gonadal development that takes place at the cost of the animal's energy reserves. When the temperature is reduced to 14 degrees C, there is a decrease in the ingestion rate and lower energy consumption, leading to a situation of positive energy balance. In these conditions gonadal development is slow and the surplus of available energy is, presumably, used to accumulate energy reserves, as is often the case during the stage of growth prior to the onset of gonadal development in many bivalves that inhabit geographical areas with noticeable seasonal variations. (c) 2006 Elsevier B.V. All rights reserved.