メコンデルタの魚相と内水面漁業(<小特集>メコンデルタの自然と農業)

Abstract

Based on the author's collection and the literature cited, 176 fish species are recorded from inland waters of the Vietnamese Mekong delta (Table 1). The ichthyological fauna of the area is characterized, in comparison with that of the Laotian Mekong, by less abundant cypriniform fishes and more numerous clupeiform and perciform species (Table 2). The mainstream waters in the delta may be divided into three sections according to faunal features, as illustrated in Fig. 1. Excepting Cirrhinus jullieni and Thynnichthys thynnoides, long-distant migratory forms found in the Cambodian and Laotian Mekong do not descend deep into the Vietnamese delta. Pangasianodon gigas, in particular, does not enter delta waters. As in other part of the lower Mekong basin, a great many species perform seasonal movement in delta waters in accordance with seasonal change in water conditions, dispersing in flooded areas during wet season and returning to rivers during dry season. Fishery productions in the delta are shown in Tables 3 and 4, together with those in neighboring areas. The delta produces 80&acd;90% of total freshwater fish production in South Vietnam. Important food fish are enumerated in Table 5. Freshwater fishes cultured in the delta are Puntius altus, P. gonionotus, Leptobarbus hoeveni, Cyprinus carpio, Pangasius micronemus, Clarias macrocephalus, Channa striata, C. micropeltes, and Tilapia mossambica. The source of fingerling for culture is natural spawning, except for the ca chep (C. carpio) and ca phi (T. mossambica). The commonest fishculture practices are the pond culture of the ca tra (P. micronemus) and the floating cage culture of the ca he (P. altus), ca loc (C. striata) and ca bong (C. micropeltes). Introduction of large-scale freshwater fisheries does not seem suitable to the delta in view of the limited productivity of the limited area of water. Aquaculture is an effective and advantageous means of utilizing land and water resources of the area. Extensive mono- and polyculture of plankton feeding and herbivorous species with pond fertilization seems most advantageous in the future. Fishculture combined with livestock, using manure from the livestock for natural fertilization of ponds, will be highly suitable to the conditions of the delta. Future changes in hydrological conditions of the delta will be various according to the nature of reformation work in the upstream areas as well as the delta. In any cases, marshy, low-lying lands, either existing or newly formed, should be retained in order to keep providing many sorts of fishes with their spawning and growing grounds.