Preliminary Feeding Ecology Of Gambusia Affinis

Gambusia affinis is one of the world's 100 evil invasive species.It was introduced to China from Manila through Shanghai in 1927,and occupied large-scale habitats in which forming many of wild populations in south of China in the past several decades. Characteristics of the digestive tract of embryo and newly birth larvae were observed by histological method,the effects of density and kind of prey item on the newly birth larvae feeding were be investigated in lab and the investigation of feeding rhythm the larvae in natural conditions also be conducted,aimed at exploring that the relationship of the larvae feeding characteristics and their invasive ability.The results showed that:1.The gap of mouth did not formed in the early stage of embryo,in which the differentiation of the digestive system,among esophagus and intestinal was not clear, while the whole digestive tract shaped a straight tube.Later,the tissues of the digestive system differentiated progressively,and perfect digestive system had been emerged at the time of the larvae birth.The construction of digestive tract can be divided into four parts:mucosal layer,submucosa,muscle layer and serosal layer.The thickness of mucous membrane and muscular layer increased during the process of the embryonic development,and the rugas of gut increased subsequently.Goblet cells mainly located in the esophagus.2.The select Index of larvae of G affinis on cladocerans was larger than 0(E＞0), indicated that they were favor on this prey type,and E＜0 on copepod indicated that they advoided this prey type or it is difficult to capture such prey,the select index E of rotifers and juvenile copepods close to 0,no apparent selectivity.Standard length and mouth width of larvae had positive relationship with the prey size.3.Feeding intensity of G.affinis larvae on worm harvest nauplii were increased with the increasing of prey density,and when the prey density reached or more than 1.6 ind/ml,it did not increase any more.4.It was very complex of mosquito fish population structure in summer,there were three feeding groups in such population:female,male and larvae.Feeding rhythms of these feeding groups were different,female feeding rhythm showed two peaks at 10:00 and 22:00,and the second was higher,while larvae fish showed two peaks at 6:00 and 18:00 also,the higher one was 6:00,and male fish had a single peak at 14:00 only.