n norouzi - M.Sc Student of Fishery Department of Gorgan university, Iran.
r ghorbani - Assistant professor of Fishery Department of Gorgan university, Iran

Our knowledge about fish biology couldn't be completed without our awareness of bio- history of larvae. The study of fish's bio- history can provide information about fish larvae actions and reactions in its first life stages. This general description can represent the anatomical, physiological, behavioral and ecological changes in development stages of fishes. In this research, we study the larvae development stages on 30 larvae of rainbow trout based on morphological observation, pigment scattering pattern and fins development pattern. From the viewpoint of pigments pattern, in general, the highest pigments were concentrated on the rear of head and between eyes and the lowest was on fins bud and their abdomen. The morphological observations in larvae stage indicated that larvae in first stage has different shape than its puberty and its appearance will change in parallel to its development during the time, so that at the end of stage, it is so like an adult fish. In same researches on larvae of other salmon species, there are relative similarities due to pigment scattering pattern but there are significant differences in morphological observation and also the pattern of fins development

Oncorhynchusmykiss , Larval development , Meristic characteristics , Morphometric variables , Pigmentation pattern