Mottled eel

Abstract: The parasitic gill monogenean Pseudodactylogyrus anguillae is alien to Africa. In an investigation of 227 longfin eel, Anguilla mossambica, and 26 mottled eel, Anguilla marmorata, sampled from four river systems in the Eastern Cape, South Africa, this parasite was only present on the gills of A. mossambica sampled from the Great Fish River system. In the Great Fish River, it infected 73.2% of the sampled population at a mean intensity of 63.8 ± 34.3 parasites per fish. High prevalence and intensity are indicative of a well-established alien invasive parasitic species. Results showing the absence of P. anguillae from the co-occurring but less abundant A. marmorata indicate that this species may be less susceptible to P. anguillae infection.

Abstract: The geographical distributions of the Japanese eel (Anguilla japonica) and Giant-mottled eel (A. marmorata) overlap in many regions in East Asia and therefore suffer from interspecific competition in the same rivers. After a long period of adaptation, the Japanese eel and Giant-mottled eel may exhibit habitat partitioning in the rivers to diminish the interspecific competition between them. In this study, we conducted a field investigation in the Fengshan River in Taiwan to survey the habitat distributions of the Japanese eel and Giant-mottled eel throughout a river. Moreover, we investigated whether their habitat distributions are related to their swimming and upstream migration. Thus, the mRNA expression levels of several candidate genes that may be associated with the swimming and upstream migration of eel were examined in the glass eels of the Japanese eel and Giant-mottled eel. Field investigation indicated that the Japanese eel mainly inhabited the lower and middle reaches of the Fengshan River, but the Giant- mottled eel was distributed over the middle to upper reaches. The mRNA expression levels of fMYH, dio2, gria3, and neurod1 were higher in the Giant-mottled eel than in the Japanese eel, implying that Giant- mottled eels might have better swimming bursts and more active upstream migration than Japanese eels. These results suggest that there is a habitat partition at which these two eel species coexist in a river, and their habitat distributions may be linked to their swimming bursts and upstream migration. Determining the habitat distributions of freshwater eels is important for developing applicable plans for eel conservation and resource management.

Abstract: The recently discovered freshwater eel species of the Luzon mottled eel, Anguilla luzonensis, has only been found in very limited area at the tip of the Northern Philippines. Here we investigated the early life history of A. luzonensis for the first time to help understand its larval dispersal pattern in the western North Pacific, and compared it to A. celebesensis and data from previ- ous studies. Genetically-identified glass eels of A. luzonensis collected from the northern Luzon Island in January and February 2009 (n=3 and 8, respectively) were used to study the age of recruitment of this species using otolith microstructure. The lepto- cephalus stage was 129.6±10.7 days (mean±s. d.; range, 113 to 146), followed by 18.4±3.7 days (13 to 25) at the metamorphosing and 17.6±5.1 days (7 to 23) at the glass eel stages. These specimens were found to be hatched between August and September 2008. A previous study on a small number of the leptocephali of A. luzonensis collected offshore reported that the hatching dates were between February and March, and thus the spawning season of A. luzonensis is suggested to span at least a half of a year.