The Studies On Feeding Behavior And Digestive Physiology In Sea Cucumber Apostichopus Japonicus

Owing to the higher nutritional value and medicinal benefits, sea cucumber (Apostichopus japonicus) has been precious marine product since ancient times. With the improvement of people’s living standard and the increase of holistic awareness, the market demand of sea cucumber is big more and more. Besides the conventional aquaculture modes of sea cucumber, industrial aquaculture of sea cucumbers has expanded rapidly becoming an important culturing mode in recent years. Knowing the basic knowledge of feeding in sea cucumber is useful for designing proper environmental factor and optimal feeding schedules. In the present experiment, we studied the effect of size, photoperiod and temperature on the feeding behavior and digestive physiology. We investigated the feeding processes by observing the tentacle and feeding rhythm by the infrared camera. In addition, we illuminated the relationship between the rhythms of digestive enzymes (protease, lipase, amylase) and feeding rhythms. The results are listed as follow:1. Feeding behavior and digestive physiology in different sizes of sea cucumber Apostichopus japonicusIn this article the tentacle locomotion, feeding rhythms, ingestion rate (IR), feces production rate (FPR) and digestive enzyme activities were studied in three size groups (small, medium and large) of sea cucumber under a 12 h light/12 h dark cycle. Frame-by-frame video analysis revealed that all size groups had similar feeding strategies using a grasping motion to pick up sediment particles. The tentacle insertion rates of the large size group were significantly faster than those of the small and medium-sized groups (.P<0.05). Feeding activities investigated by charge coupled device cameras with infrared systems indicated that all size groups of sea cucumber were nocturnal and their feeding peak occurred at 02:00-04:00. The medium and large-sized groups also had a second feeding peak during the day. Both IR and FPR in all groups were significantly higher at night than those during the daytime (P<0.05). Additionally, the peak activities of digestive enzymes were 2-4 h earlier than the peak of feeding. Taken together, these results demonstrated that the feeding rhythms and digestive physiology would change with the growth of A. japonicus, which had the ability to optimize the digestive processes for a forthcoming ingestion.2. Effects of photoperiods on feeding rhythm and digestive physiology of sea cucumber, Apostichopus japonicusIn this article the feeding rhythm, ingestion rate (IR) and the diurnal rhythm of three digestive enzyme (lipase, amylase and trypsin) activities were studied in sea cucumbers under three photoperiods (24L:0D,12L:12D and 0L.24D). The main results showed that:(1) Under the photoperiod of 24L.0D, sea cucumber had few activities and lower feeding proportion (6%-10%) within 24 hours. Under the photoperiod of 12L:12D, sea cucumber had few activities and lower feeding proportion (0%-10%) in the light and had more activities and higher feeding proportion in the dark. Under the photoperiod of 0L:24D, sea cucumber was in the active state all the time and had higher feeding proportion within 24 hours. Under all the three photoperiods, the feeding peaks of sea cucumber occurred at 00:00-02:00 and the feeding proportions were significantly higher at night than those during the daytime (P<0.05). (2) The ingestion rates of sea cucumber were increased from 24L:0D,12L:12D to 0L:24D and the ingestion rate was significantly higher at night than those during the daytime (P<0.01). (3) The peak activities of three digestive enzymes of sea cucumber appeared at 22:00-02:00 under three photoperiods and the peak activities of digestive enzymes were 0-4 h earlier than the peak of feeding. Taken together, these results demonstrated that light was a powerful environment factor that influenced rhythms of feeding and digestive enzyme activities of A. japonicus, which had the ability to optimize the digestive processes for a forthcoming ingestion.3. Effects of photoperiods on feeding rhythm and digestive physiology of sea cucumber, Apostichopus japonicusIn this article the feeding rhythm, ingestion rate (IR) and the diurnal rhythm of three digestive enzyme (lipase, amylase and trypsin) activities were studied in sea cucumbers under five temperatures (8℃、12℃、16℃、20℃、24℃). The main results showed that:(1) Under all the five temperatures, the feeding proportions didn’t vary significantly (P>0.05) in the day (8:00-20:00) but vary significantly (P<0.05) at night (20:00-8:00). In addition, the feeding peaks of sea cucumber occurred at 00:00-02:00 and the feeding proportions were significantly higher at night than those during the daytime (P<0.05). (2) With the increase of temperature, the ingestion rates of sea cucumber increased firstly and then decreased. Under all the five temperatures, the ingestion rate was significantly higher at night than those during the daytime (P< 0.05). (3) Except the condition of 24℃, the peak activities of three digestive enzymes of sea cucumber appeared at 22:00-02:00 and the peak activities of digestive enzymes were 0-4 h earlier than the peak of feeding. Taken together, these results demonstrated that temperature had a significantly influence on feeding proportion and digestive enzyme activities of different times but not their whole variant trend..