Mελέτη της διακυμαινόμενης ασυμετρίας (fluctuating asymmetry) των ωτολίθων των ιχθυονυμφών του Trachurus mediterraneus (Steindachner, 1863) ως δείκτη αναπτυξιακής αστάθειας
Developmental instability, measured as fluctuating asymmetry (FA) in bilateral traits, has widely been used as an indicator of genetic or environmental stress in a variety of plant and animal taxa. FA arises as small deviations from perfect bilateral symmetry which reflect 'mistakes' in developmental processes resulting from the inability of the genotype to effectively buffer itself against environmental perturbations. Recently, it has been proposed that FA in the otoliths can be used as an indicator of condition in larval fish. In this thesis developmental instability was studied using 4 otolith traits (maximum radius, recent otolith growth, perimeter and area) in a sample of 107 jack mackerel, Trachurus mediterraneus (Steindachner, 1863), larvae collected during June 1994 and June 1995 in the Northern Aegean Sea. The measurements of asymmetry in the 4 otolith traits were highly correlated with larvae size thus size-corrected measurements of asymmetry were used. Only perimeter and area exhibited "ideal" FA and it was proposed that two- dimensional measures of otolith size give more accurate estimations of developmental instability. There was a substantial between year difference, FA being greater in 1995 than in 1994 : in otolith area variance of unsigned asymmetry was 284% in 1995 than in 1994. Similarly, 2 growth relationships (weight, W, and anal body depth, AD on age,A) and one allometric (weight, W, on standard length, SL) were significantly different between the two years and indicated that jack mackerel larvae collected during 1994 were in better condition than those collected in 1995. In addition to the bivariate analysis of the morphometric characters a multivariate analysis(Principal Component Analysis) was contacted. The second PC distinguished the larvae of the two contrasting years accordingly to the anal body depth variable, indicating that 1994 larvae were in better condition. The was also a highly significant positive correlation between the second PC and otolith area. The results suggest that fluctuating asymmetry in the larvae otolith size is a very sensitive measure of developmental instability strongly supporting the use of the method to access nutritional condition in field collected larvae.