Study on the Behaviors of Rapana venosa Feeding on Different Bivalves

Rapana venosa is primarily distributed in the Yellow Sea and Bohai Sea of China, Japan, Korea, and Russia. In the natural sea area, the adult R. Venosa mostly inhabits the sand-mud bottom or the rocky bottom of the low intertidal zone up to 20 meters deep, and the young R. Venosa mostly inhabits the rocks near the coastal line. Its habitats are generally occupied by many other bivalves, such as Crassostrea gigas, Mactra chinensis, and Ruditapes philippinarum. The R. venosa is a large carnivorous Mollusca that mainly feeds on bivalves and other animal carcasses. R. venosa is often classified as an enemy of bivalve farming, but they can also be used to control fouling organisms, and it has potential for application in aquaculture and ocean engineering.In recent years, there have been some reports on the feeding selectivity of R. venosa, the effects of feed, temperature, and individual specifications on feeding, the effects of feed types, specifications, feeding amount, and breeding density on the survival and growth, the feeding preferences to different bivalves and the feeding cycle before and after reproduction. These studies mainly explored the effects of temperature, density, feed types, and specifications on its growth and development. The main purpose of these studies was to select suitable feed types and specifications for the temporary culture and breeding of R. venosa, to improve its growth and development speed, and increase economic benefits under artificial breeding conditions. However, the feeding selection and behavior process of R. venosa under natural conditions are not clear, and the feeding selection of R. venosa to C. gigas, Mytilus edulis and other fouling organisms was not clear under the environmental conditions of multiple bait bivalve habitats. Therefore, in this study, four kinds of bivalves (fixed type, attached type and buried type) were used as bait bivalves to understand the feeding selection. C. gigas and M. edulis are common fouling organisms in the habitat of R. venosa, while M. veneriformis and R. philippinarum are widely distributed in the habitat of R. venosa. The study attempts to simulate the habitat of R. venosa and different types of bait bivalves in the natural environment, to study its preference for bait bivalves species and feeding specifications, to compare and analyze the differences in feeding rates of different specifications of R. venosa, and further study its feeding rhythm and feeding process and to provide data reference for the feasibility of using R. venosa to control C. gigas, M. edulis and other bivalves fouling organisms, and improve the feeding habits of R. venosa.To achieve these objectives, three specifications of M. veneriformis, R. philippinarum, C. gigas, and M. edulis live baits were placed in the aquarium by simulating the natural environment. The feeding number, feeding weight, feeding specifications, feeding time, and feeding behavior process of three specifications of R. venosa to different baits were recorded. The experimental results showed that R. venosa fed on all four bivalves. The number and weight of R. venosa that fed on M. veneriformis with different specifications were significantly higher than those that fed on other bivalves (P < 0.05), and the feeding index was more than 50%, indicating its appetite. R. venosa fed normally on C. gigas and R. philippinarum, and only a small population of R. venosa fed on M. edulis with large specifications. In terms of the selection of feeding specifications, three specifications of R. venosa preferred large M. veneriformis and small C. gigas (P < 0.05). The feeding rate of the large specification R. venosa was 7.15%, which was significantly lower than that of the other two specifications (small specification, 10.98%; medium specification, 9.64%). Under the experimental conditions, the feeding cycle of R. venosa was apparent, feeding activities were carried out every three days, and the feeding time was 20:00–24:00 at night. The feeding process can be divided into four stages: Unfed stage, search stage, feeding stage, and feeding end. During the feeding process, the R. venosa actively searched for bivalves, removed them from the sand and wrapped them with their proleg, secreted mucus, and smacked them from the shell gap. After sucking the mollusks decomposed by digestive juice, the R. venosa dived into the sand or attached to the aquarium wall. The results showed that under the experimental conditions, R. venosa had a feeding preference for the species and specifications of bait bivalves. R. venosa preferred to eat M. veneriformis and rarely consumed M. edulis. Moreover, its feeding behavior was nocturnal and exhibited periodicity, feeding activity happened every three days in the first half of the night.