Do formulated feeds for juvenile Panulirus ornatus lobsters require dietary cholesterol supplementation?

Abstract

Mortality rates of wild spiny lobster seed Panulirus ornatus are typically high, with losses of 40–60% occurring within 30 days of capture. Mortality appears symptomatic of a micro-nutrient deficiency or captivity related stressors. Cholesterol is a micro-nutrient essential for healthy ecdysis, growth and survival in crustaceans. This paper reports a 7-week study examining the growth, survival and tissue cholesterol responses of juvenile P. ornatus lobsters fed a low cholesterol basal diet that was serially supplemented with cholesterol at 0.75 g kg − 1 increments from 1.25 to 4.25 g kg − 1 dry matter (DM). The basal diet contained 45 g kg − 1 phospholipid (from natural ingredients and supplemented soybean lecithin) and this was fed to all lobsters for 2 weeks prior to commencement of the experiment to reduce cholesterol reserves in the lobsters. A sixth diet comprising equal amounts of green-lipped mussel ( Perna canaliculus) and whiting fillet ( Silago ciliate) was included in the treatment array as a reference diet. One hundred and fifty lobsters were blocked by initial weight into five groups and then from within these groups they were equally distributed to 30 tanks (n = 5 tanks per treatment). There was no significant difference in survival, daily growth coefficient or tissue dry matter cholesterol content between lobsters fed the lowest and highest cholesterol diets: 55%, 349%, 243 mg 100 g − 1 and 70%, 456%, 253 mg 100 g − 1 respectively. However, there was a trend (P = 0.065) for lobster percentage weight gain to increase linearly with dietary cholesterol. There was a significant relationship between the starting weight of the lobsters and subsequent survival, with only 43% of the smallest lobsters (0.2 to 0.5 g block) surviving compared to 90% for the largest lobsters (2.71 to 3.40 g block). No specific dietary cholesterol requirement for small P. ornatus was determined. Feeds which contain practical marine proteins require no supplementary cholesterol, a significant cost saving in feed formulation. Feeds which contain high levels of plant proteins may require supplementary cholesterol to provide at least 4.0 g kg − 1 DM dietary cholesterol.