J.M. Navarro, G.E. Leiva, G. Martinez, C. Aguilera
Abstract:
Temperature and diet have been described as environmental factors playing an important role on the scope for growth of bivalves. The effects of these factors on the growth of marine bivalves have been extensively reviewed, however only a few studies have been carried out in relation to reproduction. These studies have been mainly related with gonad maturation, egg quality and larvae survival.
The main objective of the present study was to know the effects of the different combinations of two temperatures (16 and 20 C) and three diets (microalgae, microalgae supplemented with lipids and microalgae supplemented with carbohydrate) on the scope for growth of the chilean scallop Argopecten purpuratus, during reproductive conditioning. All the physiological variables related with the energy balance (energy acquisition and utilization) were measured at the different combinations of temperature and diet and related to a standard size scallop (3 g dry tissue weight). Clearance rate showed high differences with diet but not with temperature, with the highest values when the scallops were fed with Microalgae + Lipid. Net absorption efficiency was high at 16 and 20 C when the scallops were fed with microalgae and microalgae + lipids (69 to 78%). Lower values were obtained with the diet microalgae + carbohydrate, ranging between 27 and 53%. Oxygen uptake was high in A. purpuratus, with values as high as 1.6 ml O2/h for a scallop of 3 g dry tissue weight, representing a large percentage of the energy absorbed. This physiological variable did not show significant differences at the different temperature/diets combinations. Ammonia excretion represented a very small amount of the energy absorbed and it was independent of temperature and diet most of the time. To know the effects of the different combinations of temperatures and diets on the energy balance of A. purpuratus, the physiological index scope for growth (SFG) was calculated. The highest SFG was obtained with the diet microalgae + lipid at the two experimental temperatures. These results were in agreement with measurements of the gonad index, where the higher values were obtained in scallops fed with this diet. Similarly, the larger percentage of mature individuals at the end of the reproductive conditioning period, was obtained with the diet microalgae + lipid, at both experimental temperatures.
(Instituto de Biologia Marina "Dr. Jurgen Winter", Universidad Austral de Chile, Valdivia, Chile)