Basic Study On Feeding Selectivity Of Sea Cucumber Apostichopus Japonicus

This study focused on Apostichopus japonicus's feeding selectivity and developed a field study method to investigate sea cucumber's behavior, which can also be used to assess the effect of its enhancement. Histology, ultrastructure of its buccal podia, oropharynx and tube foot, feeding behavior, and immunology were studied in this research. Apostichopus japonicus's feeding selection on particle's sizes in different habitats was investigated by field survey, and compared with the result of experiments in laboratory. Besides, other experiments in laboratory were carried out to clarify its feeding selection on particle's organism content and food patches. Relationship between feeding selectivity and the structures and functions of its locomotor and feeding organs was discussed. In addition, fluorescent agent ALC was used to stain sea cucumber's spicules. Safe and effective staining time and dye concentration were studied by measuring physiological and immunological indexes. Major findings are as follows:1. The structures of buccal podia, tube foot, and mucus type were identified. Microvilli and mucus of the tentacles, oropharynx, and tube foot were observed with SEM, and its secretory cells were distinguished with TEM. Duo-gland system and feeding process of feeding were discussed to explain roles of locomotor and feeding organs in feeding selectivity. 2. Particle sizes of gut content and nature sediment were compared by field survey on Apostichopus japonicus inhabiting in a shallow bay, a cofferdam, and around a remote island. Sea cucumber selectively ingested particles 1-80μm in diameter. This result was compared with the result of an experiment in laboratory, which provided 3 diverse prepared sediments with particle size gradient to sea cucumbers with age gradient. The results of indoor experiment and field survey were seemingly contradictory, which can be explained clearly with consideration of sediment deposition characteristics and buccal podia structure.3. Apostichopus japonicus in small size obviously selected particles with high organism content, and this selectivity decreased with weight increase and organism content decrease. Heavy metal oxides which were not absorbed by animal were added into sediment patches as tracers. Preference indexes were calculated by measuring heavy metal element concentrations in all sediment patches. Experiment result showed that Apostichopus japonicus preferred food patches with low organism and chlorophyll content, refused to feed on sand with very little organism, and showed no selection towards patches with high and middle organism and chlorophyll content.4. Apostichopus japonicus was marked with ALC effectively. Besides, the safe, effective marking time (24-48h), and ALC concentration (around 80mg/L) were figured out by analyzing their effect on spicule colouring rate, survival rate, weight, and enzyme activity of SOD, CAT and GSH-Px. The safe marking time (24-48h) and calcein concentration (below 750mg/L) were also figured out by analyzing enzyme activity of SOD, CAT and GSH-Px.