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Identifier

000450027

Title

Μελέτη της αναπαραγωγικής βιολογίας του Lagocephalus sceleratus (Gmelin, 1789) και του Argyropelecus hemigymnus (Cocco, 1829)

Alternative Title

Study of the reproductive biology of Lagocephalus sceleratus (Gmelin, 1789) and Argyropelecus hemigymnus (Cocco, 1829)

Author

Γιαννουλάκη, Μαρία Μ.

Thesis advisor

Σωμαράκης, Στυλιανός

Reviewer

Κουμουνδούρος, Γιώργος
Τσερπές, Γιώργος

Abstract

This dissertation is a contribution to the study of the reproductive biology of two species: the lessepsian migrant Lagocephalus sceleratus (Gmelin, 1789) and the mesopelagic fish Argyropelecus hemigymnus (Coco, 1829). The first is a coastal, benthopelagic species originating from the Red Sea and the study of its reproduction aims at better understanding its invasion success. The second is a small-bodied, pelagic fish with poorly studied reproductive biology, like most mesopelagic fishes. The comparison of the number and the development of oocytes from the anterior, middle and posterior part of the ovary showed that, despite their large size, the gonads of L. sceleratus are homogenous. The histological analysis showed that the examined fish, which were sampled during the reproductive period, had either recently spawned (presence of post ovulatory follicles), with signs of atresia in the remaining vitellogenic oocytes, or they had not yet matured, being in the secondary growth (vitellogenesis) stage. Only one individual examined was at final maturation (germinal vesicle migration). The oocyte size frequency distributions (OSFDs) revealed that, in fish at advanced vitellogenesis or final maturation, the most developed oocytes (advanced batch) were fully separated in size from the remainder, less developed oocytes. These results suggest that L. sceleratusis a species with determinate fecundity, and, possibly, it spawns only once during the reproductive period. In the case of A. hemigymnus, the study focused on the comparison of somatic and reproductive parameters of the species between the Corinthian gulf and the Cretan Sea. The histological analysis showed that the species was reproductively active in both regions, even though the sampling took place in April in the Corinthian gulf and December in the Cretan Sea. Furthermore, the analysis of OSFDs from both regions showed that the pattern of development and recruitment of oocytes was the same: The recruitment of a new batch starts during the final maturation of the advanced batch and ends during spawning. The condition factor, the gonadosomatic index, the oocyte sizes, the relative number of oocytes >200 μm and the relative batch fecundity (eggs g^-1) had significant higher values in Corinthian gulf compared to the Cretan Sea. Even though these differences could be attributed to various causes, they are more likely resulting from the higher temperature of indermediate (mesopelagic) waters in the Cretan Sea (15 ^οC) compared to the Corinthian gulf (14 ^οC).

Language

Greek

Subject

Corinthian gulf

Crete

Reproduction

Αναπαραγωγή

Κορινθιακός κόλπος

Κρήτη

Issue date

2022-07-29

Collection