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Identifier 000334849
Title Στοιχεία βιολογίας και κατανομής του είδους Ruvettus pretiosus (Cocco 1829) στην ανατολική μεσόγειο
Alternative Title Elements for the biology and distribution of the species rurettus pretiosns (Cocco 1829) in the eastern Mediterranean
Author Βασιλακόπουλος, Παρασκευάς
Thesis advisor Παυλίδης, Μιχάλης
Abstract Ruvettus pretiosus (Cocco 1829) (Perciformes, Gempylidae), oilfish, is a benthopelagic species that can reach a length of over 2m and a weight of over 60Kg, appearing usually at lengths up to 1,5m. It presents a wide geographical distribution in tropical and temperate seas in depths from 100 up to more than 1000m, preferring depths from 200 to 600m. During the daytime the specimens of the species stay close to the bottom while at night part of the population performs vertical migrations to the epipelagic zone in search of prey. The species constitutes a by-catch of fishing gears, such as epipelagic and benthic long lines, which target more commercial species. Only scarce information exists concerning the species’ biological parameters. The present dissertation investigates the biology (growth, diet, reproduction) and the distribution pattern of the species in the eastern Mediterranean, using fisheries data. In order to study the growth, the age was calculated from the otoliths’ growth zones and backcalculation of the lengths in earlier ages was performed. The parameters of the von Bertalanffy growth equation for the female specimens, extracted from the backcalculated lengths, were L=162,14cm, K=0,273y-1 and t0=-1,60y. Those parameters were not calculated for the male specimens, due to their small number. Only the predicted lengths at age from the backcalculated lengths were calculated for males. Female specimens seem to grow faster and to reach larger size compared to males. Concerning the dietary study, stomach content analysis showed that the species is mostly ichthyophagous, feeding also on cephalopods. Specimens caught in the epipelagic zone have more usually empty stomachs than those from the benthopelagic zone, where benthopelagic preys are mostly observed. The study of the species’ reproduction patterns revealed the existence of gonochoristic sexual strategy, while fisheries data from benthic long lines revealed that the sex ratio is clearly unbalanced in favor of females at depths 250-450m. Histological analysis showed that the oocytes are characterized by the prominent presence of lipids since the earlier developmental stages. During the period from October to February, the oocytes are in resting stage, vitellogenesis starts in April and reaches a peak in June, while the reproduction period seems to be from July to August. The species spawns pelagic eggs which are expected to be very little (<1mm). Male specimens appear to be in the spermiogenic phase since the end of February. Concerning the species’ distribution in the eastern Mediterranean, testing with General Additive Models (GAMs) showed fluctuations of the species’ abundance during the last nine years, while revealing clues for a concentrated distribution in the Cretan Sea and a more random distribution in the Levantine Sea. The higher abundance appears in the area of Dodecanese and during the period from May to June. The distribution pattern is connected with the species’ dietary and reproductive needs.
Language Greek
Subject Bάτος
Issue date 2008-12-04
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Biology--Post-graduate theses
  Type of Work--Post-graduate theses
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