Reproductive behavior and parental contribution of meagre (Argyrosomus regius) in aquaculture conditions
Creators: name: Siapazis, C.
name: Fakriadis, I.
name: Gregoletto, L.
name: Tsigenopoulos, C.
name: Mylonas, Constantinos
Publisher: name: Zenodo
Year: 2023

description: INTRODUCTION
The meagre (Argyrosomus regius) is an emerging species for the Mediterranean aquaculture industry and its reproductive dysfunctions in rearing conditions have been resolved using GnRHa-based spawning induction and spermiation enhancement protocols. However, to eventually be able to obtain fertilized eggs without the use of exogenous hormones, more information about the environmental requirement of the species and its behavior during reproduction is needed. 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).
METHODS
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 in terms of fecundity, fertilization success, 24-h embryo survival, hatching and 5-d larval survival. A sub-sample of the eggs from each spawn was collected for parental contribution analysis using a multiplex of 12 microsatellite loci and an exclusion-based method.
RESULTS & DISCUSSION
Spawning induction led to three consecutive daily spawns per broodstock per year, 2 days after GnRHa administration. No statistically significant differences were observed between years or groups (2-way ANOVA, P>0.05) in mean daily relative fecundity, hatching success and 5-d larval survival. However, fertilization success (P=0.036) and 24-h embryo survival (P=0.016) were higher in Year 2. The mean daily relative fecundity (n=2) was 159,743±23,315 eggs kg-1, while mean hatching success was 98±1%, and 5-d larval survival was 96±1%. Mean fertilization success and 24-h embryo survival were 83±0 % and 93±0%, respectively for Year 1, and 92±4% and 100±0% for Year 2, respectively. 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. These spawning kinetics and productive results were similar to group and paired spawnings of meagre reported in earlier studies. The most aggressive male from Group 1 fertilized only 14±6%, while the larger one fertilized 68±9% of the eggs during the two years of the study. In Group 2, the most aggressive male fertilized 86±8 % of the eggs. The study demonstrated that hierarchies developed within meagre broodstocks, and even after exogenous GnRHa stimulation, spawning success was not equal among breeders, and a single individual of each sex dominated the produced progeny. It is not clear at this stage what factor contributes to dominance of the two sexes, but male size or aggressiveness did not correspond to enhanced parental contribution. Further analysis is underway to investigate other behavioral traits.