Phenotypic response of male and neomale of O. mykiss parr subjected to 8 degrees and 16 degrees C water temperature during early life stage

Water temperatu r e is an important modulator of variation of phenotype in poikilothermic fish and therefore of body shape. The present study explores the phenotypic response of commercial O. mykiss parr when they are subjected to rearing temperatures of 8 degrees and 16 degrees C under controlled conditions with the aim of demonstrating , with the use of Landmark-Based Geometric Morphometrics, the influence of rearing temperature on body shape. O. mykiss males and neomales from eggs to parr stages, belonging to the same family and strain, were reared at different temperatures (8 degrees C and 16 degrees C) and grouped according to: Group 16 degrees C/neomales (n = 15), Group 16 degrees C/ males (n = 15), Group 8 degrees C/neomales (n = 15) and Group 8 degrees C/males (n = 15). Differences in body shape among sex and rearing temperatures were examined by geometric morphometrics and traditional morphometry. At 16 weeks, geometric morphometric analysis revealed a dimorphism, which was not detected by traditional morphome t r y , mainly in the dorsal and caudal fin area. This dimorphism was not observed in neomales. This difference may be the product of the potential for phenotypic plasticity and adaptation to genetically controlled environmental and local fluctuations, which affects to indicators of adaptation in unfavorable environmental conditions such a biomechanical action of swimming and propulsion. In conclusion, this study demonstrates the differential effect of 8 degrees and 16 degrees C water temperature on lateral body shape in male O. mykiss parr during the early stages of body development and in controlled conditions.