Qiongwu Lin

Occurrence of follicle-stimulating hormone-like substance in the Kuruma prawn, Marsupenaeus japonicus, during ovarian maturation

Abstract The identification of vertebrate follicle-stimulating hormone (FSH) may further elucidate the reproductive mechanisms in the prawn Marsupenaeus japonicus. By immunohistochemistry, FSH-like neurons were detected in the brain and thoracic ganglia of the female kuruma prawn. By enzyme-linked immunosorbent assay (ELISA), concentrations of an FSH-like substance were determined in the brain, thoracic ganglia and haemolymph during the maturation of the ovaries. Peak levels of an FSH-like substance culminated in the brain and thoracic ganglia during the exogenous vitellogenic stage, while the maximum level of the FSH-like substance was detected in the haemolymph. Our results indicated that the vertebrate FSH-like substances are present in M. japonicus, suggesting they may be involved in the ovarian maturation.

Feeding in the megalopae of the mud crab (Scylla paramamosain): mechanisms, plasticity, role of chelipeds and effect of prey density

We used microscopic video records to analyse the behaviour of mud crab megalopae (Scylla paramamosain) fed on rotifers (Brachiomus spp.), Artemia sp. or copepods (Schmackeria dubin). The megalopae were able to capture prey whose sizes ranged from no larger than Artemia nauplii to no smaller than adult Artemia. The megalopae employed three feeding modes: (1) Ambush-Prey mode, (2) Swim-Suspension-Feed mode and (3) Sit-Sweep mode. These involved raptorial feeding, suspension feeding and an in-between raptorial-suspension feeding mode, depending on the size of the prey and their density in the surrounding water. The chelipeds played an important role in feeding. Megalopae used the chelipeds to grip or sweep prey items and their movement generated eddies that can increase feeding efficiency. To verify the contribution of the chelipeds to feeding efficiency, we observed and compared the animals under three cheliped treatment regimes: (1) Autotomized – chelipeds removed by induced autotomy; (2) Glued – chelipeds glued at the dactylus-propodus joint to eliminate their ability to grip; and (3) Control – normal chelipeds. The feeding rates of the autotomized and glued treatments were lower than those of the controls, demonstrating that the chelipeds assist in feeding but that the megalopae can still feed without them. The density of prey also affected feeding efficiency. Feeding rate and prey density were positively correlated. When prey density was high, megalopae were able to feed in excess of their nutritional requirements. The study shows that mud crab megalopae respond flexibly to variations in feeding conditions, such as damaged chelipeds, as well as prey size and density. We postulate that this plasticity evolved in response to the dilute and patchy prey conditions of the estuarine environment. All the analysed behaviours are illustrated with video sequences.