The reproductive biology of the school shark, Galeorhinus galeus Linnaeus 1758 (Chondrichthyes: Triakidae), from the Maghreb shore (southern Mediterranean)

摘要

Pas butor, Galeorhinus galeus uobičajeno se lovi u južnom Mediteranu izvan obale Magreba, uzduž alžirske i tuniske obale. Od 517 primjeraka, sabranih kroz više od 20 godina, najmanji adultni mužjak bio je dug 1225 mm (TL) i težio je 11580 g, a najveći je imao dužinu od 1580 mm i težinu od 19900 g. Svi mužjaci, dužine veće od 1260 mm TL, bili su odrasli. Odrasle ženke imale su 1400 - 1900 TL. Najmanja ženka s embrijima u razvitku imala je 1400 mm TL. Najveća ženka imala je TL 1990 mm i težila je 27900 g. Uobičajeno su ženke bile teže od mužjaka, iako nije postojala signifikantna razlika između mužjaka i ženki s obzirom na odnos mase i ukupne dužine. Postoje 2 ovulacije i dva razvoja mladih - zimi i u proljeće. Procijenjeno je da trudnoća traje 12 mjeseci. Glavnina ženki se razmnožava u naizmjeničnim godinama. Promjer najveće oocite sa žumanjcem iznosio je 43-47 mm (prosjek 44,7 ± 2,2). Oba uterusa bila su podijeljena u komorice i u svakoj od komorica se razvijao po jedan embrij. Dužina i težina kod rođenja, mjerena na embrijima vrlo bliskog datuma, procijenjene su na 240 -320 mm TL i 88 - 109 g. Kemijska ravnoteža razvoja, bazirana na prosječnoj suhoj težini najvećih oocita sa žumanjcem i embrijima bliskog vremenskog razdoblja, bila je oko 1, što znači da se G. galeus može smatrati semi-lecitotrofnom vrstom. Ovarijska plodnost bila je veća od uterine plodnosti.%The school shark, Galeorhinus galeus, is commonly captured off the Maghreb shore along the Algerian and Tunisian coasts of the southern Mediterranean. Of 517 specimens collected during more than twenty years, the smallest adult male was 1225 mm total length (TL) and weighed 11 580 g, the largest adult male was 1580 mm and weighed 18 000 g, and the heaviest male was 1570 mm and weighed 19 900 g. All males above 1260 mm TL were adult. Adult females were 1400-1900 mm TL. The smallest pregnant female was 1400 mm TL and carried developing embryos. The largest female was 1990 mm TL and weighed 27 900 g. Females were generally heavier than males, but there was no significant difference between males and females in mass versus total length relationship. Two ovulation and two pupping seasons occurred in winter and in spring. Gestation was estimated at twelve months, with most females appearing to reproduce in alternate years. The diameter of the largest yolky oocytes ranged 43-47 mm (mean 44.7 ± 1.8) and the mass ranged 45-52 g (mean 47.9 ± 2.2). Both uteri were compartmentalized into chambers and a single embryo developed in each chamber. Length and weight at birth, based on near-term embryos, were estimated at 240-320 mm TL and 88-109 g. The chemical balance of development, based on the mean dry mass of the largest yolky oocytes and of near-term fetuses, was about 1, showing that G. galeus can be considered as an incipient histotrophic species. Ovarian fecundity was higher than uterine fecundity. Litter sizes ranged 8-41. Males generally outnumbered females, especially among free-swimming adult specimens.