The effect of feeding and diet on the hepatopancreas of New Zealand’s two rock lobster phyllosoma Jasus edwardsii and J. verreauxi

Abstract

The hepatopancreatic cells of Stage III Jasus edwardsii and J. verreauxi phyllosoma were investigated to establish whether they have similar cell types to those found in other larval decapods. The hepatopancreas cells are important because they contain the energy stores and reflect the nutritional state of phyllosoma. The cells were examined by light and electron microscopy. Four cell types were identified; E-, B-, F- and R-cells. These cells are morphologically similar to equivalent cells found in other decapods, and probably have a similar function based on their ultrastructure Initial energy reserves of newly hatched J. edwardsii and J. verreauxi phyllosoma were examined. In both species, phyllosoma are released in batches over a period of 3 - 5 days. This study aimed to establish whether any particular batch of phyllosoma had a greater level of energy reserves. The level of energy reserves was measured by the length of time phyllosoma could survive until death. J. edwardsii phyllosoma released on days 2 and 3 of the hatch had the greatest level of energy reserves but no difference was observed between the different batches of J. verreauxi phyllosoma. In both species a difference was observed between phyllosoma originating from the different sized females. Phyllosoma that originated from the larger females tended to have greater energy reserves than those originating from smaller females. However, due to the small sample size, further investigation is needed to verify this observation. The effect of initial starvation and duration of feeding period on survival and intermoult period of newly hatched J. edwardsii and J. verreauxi phyllosoma was investigated. The phyllosoma were fed Artemia brine shrimp and reared from Stage I to Stage II. The 50% level of point of no return (PNR50) was estimated at 5.23 days for J. edwardsii and 2 days in J. verreauxi. The 50% level of point of reserve saturation (PRS50) was estimated at 4.6 days in J. edwardsii, and 7.8 and 9 days in the two J. verreauxi experiments. These results suggest that Stage I J. edwardsii phyllosoma have greater energy reserves than J. verreauxi. Starvation affected all the hepatopancreatic cells of phyllosoma, but the R-cells reacted more abruptly, undergoing dramatic ultrastructural changes as starvation was prolonged. Three different diets (Brine shrimp Artemia, brine shrimp based pizza, and mussel Mytilus galloprovincialis) were fed to Stage III J. edwardsii and J. verreauxi phyllosoma to investigate the effect of diet on the survival and hepatopancreas cells of the phyllosoma. Brine shrimp produced the highest survival followed by the pizza diet and then mussel. A starvation treatment was used as a control. The hepatopancreatic cells were examined by light and electron microscopy. Most cells, but particularly the R-cells showed histological variations between the different diets. This suggests that R-cells can be used to monitor the nutritional value of diets. All the diets caused the R-cells in the phyllosoma to show signs of malnutrition. It is therefore concluded that although some food types produce high survival, monospecific diets should be avoided.