Effects of starvation and recovery on growth, proximate composition and RNA/DNA ratio in juvenile spotted ivory shell (<I>Babylonia areolata</I>)

Abstract

To investigate the compensatory growth responses of the scavenging gastropod Babylonia areolata,a refeeding after starvation study was performed at (25.8±1.7) ℃. Juvenile spotted ivory shells weighing a mean of 5.25 g were starved for 7 (S7),15 (S15),25 (S25),and 40 (S40) days,respectively,and then fed to satiation once a day during the 30 days refed period. The four corresponding control groups were fed to satiation during the experiment. Three tanks each containing 30 snails made up a group. The results indicated that the water contents of the whole soft body increased gradually during starvation,and was significantly higher than that of the control when the snails were fasted for 15 days (P0.05). The lipid and glycogen contents were significantly lower than those of the controls when food were prohibited for 15 days and 25 days respectively (P0.05),while there were no significant differences in protein contents (P 0.05 ). The ratios of RNA/DNA in foot muscle and hepatopancreas of the snails both decreased gradually during the fasting period. After 30 days recovery growth,except for the water content in the S40 group,which was significantly higher than that of the control (P0.05),there were no significant differences in other biochemical composition between refed and control groups(P0.05). The ratios of RNA/DNA were near or markedly higher than that of the control except in hepatopancreas of the S40 group which was lower than that of the control (P 0.05 ). The feeding rate (FR) during refed period was higher (for S7,S15) or significantly higher (for S25,S40) than that of the controls which were fed throughout the experiment,there were no significant differences in food conversion efficiency (FCE) and increments of body weight between the S7,S15,S25 groups and their controls respectively,as well as no significant differences were found between the S7,S25 groups and the controls respectively as to specific growth rate (SGR) (P 0.05 ),while the SGR was markedly higher than that of the control in the S15 group (P 0.05 ). Whereas there were significant decreases in the FCE,SGR and increment of body weight for the S40 group,although the FR of this group was greatly increased compared to the control (P0.05). In conclusion,the snails could utilize lipid and glycogen first as energy resource when being deprived of food,and there is complete compensatory growth in snails as the starvation period was no more than 25 days. The results of the present study indicate that prolonging the feeding intervals properly can facilitate the culture manipulation and spare food under the premise of not affecting the growth rate of the snails,and the RNA/DNA ratios in the two tissues are a valid indicator of nutritional condition in spotted babylon juveniles.