Sex-specific advance in pubertal maturation in response to in vivo application of recombinant Fsh and Lh to prepubertal meagre (Argyrosomus regius)

INTRODUCTION Biotechnologies to advance pubertal maturation and spawning would enable the aquaculture industry to accelerate genetic improvement in late maturing fish, such as meagre (Argyrosomus regius). Follicle stimulating hormone (Fsh) initiates pubertal maturation and combined with luteinizing hormone (Lh) controls gametogenesis through to spawning. The aim of the present study was to determine the in vivo effect of recombinant gonadotropins (rGths), rFsh and rLh, administered to prepubertal meagre. METHODS Gonadotropin sequences were used to produce meagre single-chain recombinant gonadotropins, rFsh and rLh using the CHO expression system (Rara Avis Biotec, S. L.). Prepubertal meagre, (≈18 months old, 1.07 ± 0.18 kg mean ± SD) were randomly distributed into rGth treatment (n=36) and control (n=36) groups and housed in a 10 m3 tank under natural photoperiod (Oct. – March) and constant temperature (18.1 ± 0.3°C). A 21-week experiment was initiated on Oct. 27 in which the treatmed fish received weekly injections of a combination of rFsh (6 to 12 μg kg-1) and rLh (3 to 10 μg kg-1), and control fish saline injections. Gonadal development was assessed by GSI and histology on weeks 0 (n=12) and in both groups (n=12 group-1) on weeks 6, 12 and 21. Plasma 17β-estradiol (E2) and 11ketotestosterone (11-KT) were determined for groups (n=12 group-1) on weeks 0, 4, 6, 8, 12, 16 and 21. RESULTS & DISCUSSION The rGth treatment increased male maturation from 12.5% (Control) to 100% (rFsh + rLh). Males in the rGth group had a GSI of 1.9±0.2% (week 12), with testes full of luminal spermatozoa and free flowing spermiation of motile spermatozoa compared to non-maturing control males that had no presence of sperm, a GSI of 0.2±0.1% and testes containing mainly spermatogonia and spermatocytes. Testes development was driven by significantly elevated 11-KT plasma levels in the rGth group (weeks 6 to 21). In comparison females were not induced to mature and oocytes remained almost exclusively at primary growth, perinucleolar stage. Plasma levels of E2 remained low (50.8±12.3 to 104.4±12.4 pg mL-1) across all groups and dates. The female GSIs were low between 0.1 ± 0.0 and 0.3 ± 0.1 %, but the GSIs of rGth treated females were significantly higher than control females on weeks 12 and 21. Four females (from 10 females, i.e. 40% - week 12 and 21 combined) had a low frequency (0.1 %) of oocytes in the early stages of vitellogenesis. The response to the rGth treatment to 18-month-old / 1 kg meagre was sex specific, as males matured and females did not mature. These findings suggest that ovaries had not fully developed the follicle structure with Fsh receptors and were not able to receive the rFsh signal to produce E2 and initiate puberty. Normally, female meagre enter puberty a year after males and appear to require more time to develop before puberty can be induced using rGths. The study was funded by the European Union´s Programme H2020, project NewTechAqua, GA 862658.