The effect of starvation on refeeding, digestive enzyme activity, oxygen consumption, and ammonia excretion in juvenile white shrimp Litopenaeus vannamei

Abstract

Juveniles of the white shrimp Litopenaeus vannamei were kept Without food for between 0 to 15 clays to evaluate the impact of starvation oil physiologic state (oxygen consumption, poststarvation refeeding, index, nitrogen excretion, and O:N ratio) and digestive enzymes activity. Physiologic changes were found after 6 days of fasting, and refeeding ability declined as a result. Nevertheless. the shrimp were able to Survive 16 days Without food. Starvation Caused metabolism to drop progressively toward a basal level (21 J (.) h(-1 .) g(-1)) and a decrease in the rate of ammonia excretion, because of the catabolism of amino acids front soluble protein in the hepatopancreas. This decrease led to an increase in digestive enzymes specific activity (U/mg protein). But, expressed as total U. all digestive enzyme activities decreased in the absence of substrate from 0.016 to 0.007 U/hepatopancreas (HP) for alpha-amylase and 2.58 to 0.63 U/HP for total trypsin. L. vannamei juveniles showed a true physiologic adaptation mechanism to food depiivation: no changes in body weight but loss in hepatosomatic index, no exuviations, including the utilization of HP soluble proteins (a drop from 269 to 53 mg/mL). After 10 days. a neoglycogenic pathway and the corresponding tissue enzymes activities seemed enhanced, and the animals derived all energetic Substrates mainly from protein (O:N ratio of 17) to cover their metabolic costs. Estimates of basal metabolism (Hem) from the routine respiration rate per clay (from 361 to 725 J (.) g ww(-1) (.) day(-1) through the 15-day starvation period). and loss of nonfecal energy (HxE) from the nitrogen excretion rate (varying from 39 to 57 J (.) g ww(-1) (.) day(-1) during the same period) were used in a bioenergetic partition model of a fasting juvenile. Which indicated that the energetic requirement to Survive Without feeding was in the range of 418 and 771 J (.) g ww(-1) (.) day(-1) during the 15-day period of starvation.