Ontogenetic patterns of growth and lipid composition changes of blue swimmer crab larvae: insights into larval biology and lipid nutrition

Abstract

Blue swimmer crab, Portunus pelagicus, is a commercially important crab throughout the Indo-Pacific region, that plays an important role in the food chains of coastal ecosystems. P. pelagicus undergoes four pelagic zoeal stages and a post-larval megalopal stage before settling as benthic juvenile; however, very limited information is available on larval biology and lipid nutrition of this species. The present comprehensive study investigated survival, growth and ontogenetic changes in lipid composition of P. pelagicus larvae under laboratory conditions. Larvae were fed rotifers (zoea I), rotifers and Artemia (zoea II) and enriched Artemia (zoea III – megalopa), consecutively. Among five larval stages of P. pelagicus, zoea I and II had the shortest durations (2.2–2.3 days), whereas megalopa had the longest duration (4.7 days). As larvae developed, their wet weight, dry weight and carapace length increased exponentially. Lower mortality occurred during zoea II (12.5%) and zoea III (14.3%), coincidental with the lower percentage increments in dry weight and specific growth rate of dry weight during these two stages. Generally, fatty acid composition of larvae can reflect that of their diets. However, increases in mono-unsaturated fatty acids, 20 : 4n-6 and 22 : 6n-3 in megalopa and the first crab compared with zoea IV might suggest that the later larvae were still deficient in essential fatty acids, and that 20 : 4n-6 and 22 : 6n-3 were preferentially accumulated. Therefore, measures of ontogenetic patterns of growth and lipid composition will provide valuable insights for better understanding of larval biology and lipid nutrition of P. pelagicus.