The number of spots on the flank of the Mediterranean trout Salmo cettii population from Tellesimo Stream in Sicily, Italy, varied between seven and 37, with a median and mode of 21, numbers much lower than those reported in the literature and different from those of other Italian trout populations. This finding could be ascribed to the phenotypic plasticity of the species or, alternatively, could provide evidence to support the different origin of Sicilian autochthonous trout. Given the ease of use of this character for the identification of native fish, it could be particularly important for conservation and management purposes.
Summary
This study reports the first available data on the reproductive biology of an Italian Salmo cettii trout population. Fecundity, egg and larvae size were determined in 38 females collected by electro‐fishing before spawning (January–February, 1993 and 1994) in the River Irminio (SE Sicily, Italy; 36°57′36″N; 14°46′18″E), probably the southernmost trout river in Europe. The smallest ripe female was 16.3 cm long and the largest 31 cm (SL). Fecundity was described according to: Log F = −0.669 + 2.592 × Log SL, which is comparable to the most fecund European trout populations. This can be explained by the productivity of this river: on the basis of the results it was not possible to use fecundity to discriminate between nominal brown trout and Mediterranean trout (i.e. no taxonomic fecundity differences were found) nor to show clear‐cut differences in fecundity between Atlantic and Mediterranean habitats. Bigger females produced significantly larger eggs, which in turn produced significantly longer alevins at hatch. This significantly positive relationship was still present after 15 days and at the resorption of the yolk sac. The interplay between high fecundity and large egg diameter (i.e. high allocation in egg mass) could be particular to this trout, and produced very high GSI values that showed no significant relationship to length. The data reported in this study are particularly important for the design and implementation of effective management and conservation measures for this threatened trout species.
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