~ 125 ~ International Journal of Fisheries and Aquatic Studies 2016; 4(4): 125-129 ISSN: 2347-5129 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.352 IJFAS 2016; 4(4): 125-129 © 2016 IJFAS www.fisheriesjournal.com Received: 17-05-2016 Accepted: 18-06-2016 Maulilio J Kipanyula Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Sokoine University of Agriculture, P. O. Box 3016, Chuo Kikuu, Morogoro Tanzania Keziah W Maina Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Sokoine University of Agriculture, P. O. Box 3016, Chuo Kikuu, Morogoro Tanzania Correspondence Maulilio J Kipanyula Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Sokoine University of Agriculture, P. O. Box 3016, Chuo Kikuu, Morogoro Tanzania Morphological and adaptational changes associated with fish migration from fresh to marine water bodies Maulilio J Kipanyula and Keziah W Maina Abstract Expansion of the aquatic industry and increased preference on white over red meat has resulted into intensification of aquaculture practices. Inland capture fisheries in Africa are also on the increase while marine capture has stagnated over the last 20 years. This has led to unconventional fish farming where by some marine and fresh water fish species are increasingly farmed in fresh and sea waters respectively. Although some fish species can naturally survive on fresh and sea water environments, the transition between the two water bodies requires morphological changes to ensure survival and optimal productivity. Morphological changes take place concurrently, with the physiological adaptations which are critical for survival in the new environment. Artificial hatcheries can simulate environmental conditions which favour such transitions, and therefore proper understanding of the underlying anatomical and physiological changes is crucial. In this paper, we summarize and discuss available reports on the anatomical and physiological changes associated with migration of fish from fresh to sea water and vice versa. Understanding of species specific adaptational changes is crucial as farmers engage in intensive fish farming involving transfer from hypoosmotic to hyperosmotic water environments and vice versa. Keywords: Smoltification, fish, fish hatcheries, parr. Introduction Some fish species inhabit both freshwater and seawater bodies and routinely migrates between the two environments [1] . The transition between water bodies lead to anatomical changes such as: change in pigmentation, body shape and length, emergence and growth of teeth on the maxilla, mandible and tongue; growth and changes in shape of integumentary folds adjacent to the cloacal opening; growth and change in shape of the auxiliary appendage of the pelvic fin; and growth in the scales with respect to radius and number of circuli. Additionally, adaptational morphological changes also occur in the gills, esophagus, kidney and intestines [1, 6-9] . Migration between fresh and marine water ecosystems is often associated morphological changes referred to as smoltification or parr-smolt transformation and the resulting migrant is termed a smolt, which is characteristic of juvenile fish. In this context there are two groups of fish namely as; catadromous and anadromous fish [2] . Catadromous fish are born in saltwater, then migrate to freshwater as juveniles where they grow into adults, before migrating back to the ocean to spawn. The catadromous fish include; true eels (Anguillids spp), thin-lipped grey mullets (Liza ramada) and European flounders (Platichthys flesis). This metamorphosis involve alterations in lipid metabolism, osmoregulation, oxygen transport, buoyancy, growth, colour, shape, rheotaxis and behavior are preparatory events to maximize survival during downstream migration, ocean entry and long distance feeding migrations in the marine environment [1]. In anadromous fish reproduction is limited to rivers which have few predators thus increasing chances of survival during the early stages. The river ecosystem supports limited growth rate and size of fish, therefore by leaving at a certain life stage and entering ocean which has rich marine food supply, they increase their reproductive success. The age at which smoltification occurs and its intensity differ among species. For example; in pink salmon (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) seaward migration takes place soon after emergence from the gravel and the rest of the life cycle and growth takes place in the sea. The Charr (Salvelinus spps) are entirely fresh water or spend only a few weeks feeding in sea water during summer.