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Identifier

000454252

Title

Αναπαραγωγική συμπεριφορά του κρανιού (Argyrosomus regius) σε συνθήκες υδατοκαλλιέργειας

Alternative Title

Reproductive behavior of meagre (Argyrosomus regius) in aquaculture conditions

Author

Σιαπάζης, Χρήστος Α.

Thesis advisor

Παυλίδης, Μιχαήλ

Reviewer

Μυλωνάς, Κωνσταντίνος
Παπαδάκης, Ιωάννης

Abstract

Meagre (Argyrosomus regius) is a sciaenid species of high commercial interest for Mediterranean aquaculture. Despite the increase in production, the species exhibits reproductive dysfunction in captivity, which have been resolved using GnRHa-based spawning induction and spermiation enhancement protocols. However, the contribution of each breeder in each reproductive event and the reproductive behavior and the relevant dominance relations in each broodstock has not been investigated. The aim of this study was to describe the reproductive behavior and parental contribution of meagre in aquaculture conditions, after spawning induction with gonadotropin releasing hormone agonist (GnRHa). Two meagre broodstocks (Group 1 and 2, 2 females and 3 males, each) were utilized for two consecutive years (Year 1 and 2). At the expected spawning period, reproductive stage was evaluated, through ovarian biopsies and sperm quality evaluation, and fish were induced to spawn with GnRHa. Each breeder was externally tagged, and their behavior was monitored using underwater equipment. Egg production and quality was evaluated and a sub-sample of the eggs from each spawn was collected for parental contribution analysis. Spawning induction led to three consecutive daily spawns per group per year. The mean latency period was found 34.1±0.9 h post GnRHa administration. The mean daily relative fecundity (n=2) was 159,743±23,315 eggs kg^-1, while mean fertilization success was 83±0 % and 93±0%, for Year 1 and Year 2, respectively (P=0.036). Parental contribution analysis showed that 77±3% of the eggs were produced by the same female, while 77±9% of the eggs were fertilized by the same male in each group for both years. The heavier among male breeders in Group 1 fertilized 68±22% of the eggs during the two years of the study. In addition to aggressive behaviors, the behavior of meagre spawners was found to include “trailing” phenomena. In this phenomenon, at least one male spawner found to spend time following a female spawner. The average tracking time over the recording period was found to be 197±49 min and the trailing phenomenon was found to occur on average 64±44 times. The behavior of the meagre breeders was found to include phenomena of "clinging" and group swimming of all male spawners towards a female ("darting"), the "darting" phenomenon increased during the second breeding season. All reproductive events (spawning) were found to occur after sunset, with one exception. Each reproductive event was found to involve one female while the participating males were one up to the total number of male spawners in the group. The mean duration of the reproductive event was found to last 0.91±0.06 min and included the attachment of male spawners to the female, group swimming and simultaneous release of gametes. Finally, behaviors were observed that did not appear to be associated with reproduction. These behaviors included group swimming "schooling" and “resting” were meagre breeders were staying at the bottom of the tank without interacting with the rest of the breeders or participating in any evolving phenomena in the tank. Mean duration of the phenomena was 237±37 min for "resting" and 125±11 min for "schooling". The present work presents for the first time the behavior of meagre spawners after spawning induction using GnRHa. The behavior of the spawners is distinguished by both samesex and different-sex phenomena. The contribution of male spawners to fertilization appeared to be influenced both by the size of the breeders and by the signs of dominance through the attacks they induced.

Language

Greek

Subject

Parental contribution

Spawning kinetics

Αναπαραγωγή

Γονική συνεισφορά

Συμπεριφορά γεννητόρων

Issue date

2023-03-24

Collection

School/Department--School of Sciences and Engineering--Department of Biology--Post-graduate theses