Larval culture of Tachypleus gigas and its molting behavior under laboratory conditions

Abstract

Horseshoe crab populations along the northeast coast of India are under threat due to degradation of the breeding beaches. To augment the trend, attempts were made to culture the larvae of Tachypleus gigas and study its growth rate by enhancing the molting pattern in the laboratory condition. Trilobites of T. gigas were cultured on a controlled diet of brine shrimp (Artemia) and diatom (Chaetoceros gracilis) at 26-28°C and 32-34‰. Trilobites could molt up to the fourth posthatched juvenile stage within a period of 180 days from the day of hatching of trilobite from the egg membrane as free swimming larval stage. The molting behavior was faster from the first to the third posthatched juvenile stage, i.e., within a period of 90 days. The average growth rate in terms of total body length from the first to second posthatched juvenile was about 63%, and from the second to third posthatched larva was about 38%. The growth rate was found to be about 25% from the third to fourth posthatched juvenile stage, and molting took place 180 days after the day of hatching of trilobite. All the posthatched juveniles had similar morphological features to the adults. The fourth posthatched juveniles exhibited more prominent morphological features with fully grown legs, spines, and segmentation, with a total body length of 45 mm. Further studies on food-dependent molting patterns of juvenile instars may help to establish a standardized aquaculture method to grow horseshoe crabs in captivity. Sea ranching of these reared animals can be carried out regularly in the holding areas to increase horseshoe crab populations and conserve these precious organisms from the brink of extinction. © Springer Science+Business Media, LLC 2009. All rights reserved.