Interspecific Relationship Between The Invasive Species Gambusia Affinis And The Native Endangered Species Tanichthys Albonubes

Biological invasions have long been recognized as a major cause of fish species population decline. The mosquito fish Gambusia affinis, a small fish which is native to North America, is one of the world's one hundred evil invasive species. Its invasions have led to great damages to the invaded wetland habitats. It was originally introduced to China in 1927, and dispersed rapidly since then. At present, it had occupied large scale freshwater habitats in south of Changjiang River in China. However, it was rare study concerned about its invasions ecology in China to date.Tanichthys albonubes, a native endangered small freshwater fish in South China, inhabits in headwater streams and the conjoined drainages of rice fields and marshes in small hill regions. It was suspected that its endangered would have some unconcerned relations with the invasions of G. affinis.The aim of this paper is to explore the interspecific interaction between T. albonubes and G. affinis, and to determine the invasion effects of G. affinis on Tanichthy albonubes. The results of this study may provide a new insight on the relationship of G. affinis to the native small freshwater fish species in South China, and will facilitate the theory developments of invasion ecology and conservation biology of freshwater fish species. Particularly, it will provide the critical theoretical direction to the practices of T. albonubes conservations.The main results are:1) In field conditions, it was revealed that the G. affinis had invaded into many of the habitats that T. albonubes naturally occupied in Conghua county, Guangdong province, China. Particularly, it had invaded into the lower parts of the headwater streams that are the main habitats of T. albonubes, and showed the trends to further spread in these habitats. In contrast, G. affinis had showed a co-occurring with the T. albonubes in the drainages of rice field. It suggested that G. affinis performed predation effects on the larval T. albonubes in those co-occurring sites, leading to lower ratio of total length between the T. albonubes populations in sites of invaded or un-invaded by G. affinis. 2) In laboratory conditions, firstly, it was revealed that G.affinis predated on the larval T. albonubes that were smaller than 12mm (total length) heavily, however, the larval T. albonubes did not show any recognition on this strange predator. Secondly, it was revealed that the presence of G.affinis may disrupt the reproductive behaviors of the paring adult T. albonubes, and cause failures on their reproduction by its bites. Thirdly, it was revealed that T. albonubes is a successive spawner, and daily spawning made the T. albonubes obtain the highest total eggs production and high fertilization rates in laboratory conditions.3) In micro ecosystem conditions, it was revealed that G. affinis significantly suppressed the increasing of T. albonubes populations. In contrast, after the G. affinis were eliminated, the T. albonubes populations recovered to normal increasing. On the other hand, it was proven that the presence of G. affinis did not affect the mature of the juvenile of T. albonubes in micro ecosystem conditions. Thus, the main effects of G. affinis on T. albonubes in micro ecosystem conditions should be its predation on the larval T. albonubes, not the effects on the gonads development of T. albonubes.4) The commons of wild population ecology traits in these two species are:small size of individuals, short life span, short time to mature and high complex in population constructions. In addition, these two species shared many another common population ecology traits in local conditions in Conghua, Guangdong province, China, such as the similar annual dynamics of gonadosomatic index, both no more than one year in life span, both can reproduced in most of the time of a year. On the other hand, raining had dramatic effects on their interspecific interaction in field. It bring the T. albonubes from the un-invaded sites to the invaded sites which invaded by G. affinis by the strong flow in raining seasons. Thus, the real interaction effects between G. affinis and T. albonubes will be masked, and led to the misunderstanding, that is, T. albonubes can co-inhabit with G. affinis infield.