Effects of fish visual stress and kairomone on the growth and reproduction of Daphnia magna

Abstract:

There are various reasons for the miniaturization of zooplankton in subtropical areas and the current view of many scholars is inclined to the predation pressure of fish. In this experiment, Pseudorasbora parva and Daphnia magna that are common in the middle and lower reaches of the Yangtze River were chosen as the research object. The two species were cultured in the same container but P. parva couldn't prey directly on D. magna. On such a premise, a cross-over experiment was designed to study the effects of visual stress and kairomone on the growth, body size and reproduction of D. magna. The study was divided into four groups, namely, the non-visual stress kairomone group, the visual stress kairomone group, the non-visual stress non-kairomone group, and the visual stress non-kairomone group. Results indicated that:the body length of D. magna increased more rapidly in the absence of kairomone; The spine length of D. magna increased more rapidly in the absence of kairomone, and the spines were longer under visual stress; The average reproduction of D. magna was 2.89 times higher in the absence of kairomone, and the visual stress kairomone group had the fastest death rate. Although biological manipulation has reduced the number of cladoceran predators, the residual fish kairomone in water remains to inhibit the cladoceran in aquatic ecosystems. The results showed that fish not only have direct feeding pressure on cladoceran, but also have indirect effects on cladoceran body size, growth and reproduction through visual stress and kairomone.