Caratterizzazione zootecnica, morfometrica e genetica di ceppi di trota iridea (O. mykiss) utilizzati in acquacoltura

ENGLISH ABSTRACT This study aimed at analysing the major biotic and abiotic factors that influence the rainbow trout (O. mykiss) productive yield in the Trentino region (Northern Italy). Five were compared for their overall farming performance and suitability to be reared in the local farms. Eyed-egg samples of different strains were obtained from local and foreign suppliers. In the first part of the trial, the strains were compared in terms of egg size, hatching and growth rates up to the parr stage in a single farm and the intraspecific genetic variability was assessed using a microsatellites technique by analysing DNA extracted from random samples of caudal fin tissue. This method yielded evidence of genetic differences among different stocks and after 8 rearing months in zootechnical performances too. In the second phase of the trial, parrs of each strain were divided into 4 lots. Then the lots of the 5 strains were transferred to 4 selected local trout farms to carry out a performance test up to a market size of around 0.7 kg. Regardless of the location, all fish lots were kept at the same density and were fed the same commercial trout feed, six days a week. Individual weight and length were measured on random samples of 100 fish per lot every 2 months. At the same time, major water parameters were registered in the different farms. Specific growth rate (SGR), thermal growth rate (TGR), condition factor (CF) and feed conversion ratio (FCR) were calculated. Statistical analyses were performed with SAS and STATISTICA 9.0. At the end of zootechnical trial a random samples of 50 fish from each batch were slaughtered then processed in the food industry. The main biometric measurements were collected on whole fish and during the processing phases on the fillet and on the by-products as head, guts and bones. The main biometric indices were calculated: condition factor, relative profile, agility index, cranial index and visceral index. All data were analysed by SAS and STATISTICA 9.0 statistical programmes. Furthermore the intraspecific variability is assessed using the geometric morphometric analysis. This morphological technique provides information on phenotypic stocks or groups of individuals and moreover on environmentally induced phenotypic patterns. Among-strains differences in growth performance, condition factor, feed conversion and age at sexual maturity were found at market size and during the processing phases too, as fillet yield and biometric indices. The morphological method yielded evidence of differences among different stocks and fish plant.