Recombinant Fsh and Lh therapy for spawning induction of previtellogenic and early spermatogenic arrested teleost, the flathead grey mullet (Mugil cephalus)

Abstract

With the expansion and diversification of global aquaculture, efforts continue to develop new bio-technologies for assisted reproduction in species that present reproductive dysfunctions. Flathead grey mullet (Mugil cephalus) held in intensive conditions in the Mediterranean region, display a severe reproductive dysfunction, where males do not produce fluent milt and females are arrested at previtellogenesis or early stages of vitellogenesis. In the present study, weekly injections of species-specific single-chain recombinant gonadotropins (rGths); follicle stimulating hormone (rFsh) (6 to 12 μg kg-1 doses) and luteinizing hormone (rLh) (2.5 to 24 μg kg-1 doses) were administered to induce vitellogenesis, from previtellogenesis / early vitellogenesis to the completion of vitellogenic growth in females and enhance spermatogenesis to produce adequate volumes of sperm from non-fluent males. During the experiment, all treated females (n = 21) developed oocytes in late vitellogenesis with 603 ± 8 μm diameter and all treated males produced fluent sperm. To induce oocyte maturation, ovulation and spawning, females were treated with either (i) a priming dose of 30 μg kg-1 of rLh and a resolving dose of 40 mg kg-1 of progesterone (P4), (ii) priming and resolving doses of 30 μg kg-1 of rLh, or (iii) priming and resolving doses of 40 mg kg-1 of P4 given 24:05 ± 0:40 h apart. Females were placed in spawning tanks with rGth treated males that had fluent sperm. Spontaneous spawns of fertilised eggs were obtained after inducing with rLh + P4 or rLh + rLh (priming and resolving injections) with a spawning success of the 85% (8 of 9 females) and 100% (n = 6), respectively. The eggs collected from the tanks presented 64 ± 22% fertilization with embryo development and 57 ± 24 % hatching. The treatment P4 + P4 had a lower ovulation success (50 % - 3 of 6 females) and spawning success (17 %) with no fertilised eggs. Success was independent of the initial gonadal stage of females. In comparison, control females did not show any advance in gonadal development from initial stages and control males did not produce fluent sperm. The present results confirm the possibility of controlling oogenesis from previtellogenesis to the completion of maturation and fertilised tank spawning using exclusively rFsh and rLh in a teleost species.

Spawning induction for Latin American fishes

“…Type 3 dysfunction occurs when oogenesis is complete with ovulation but spawning or the courtship are not completed to produce viable eggs and fertilise the ova. Despite of the recent success of studies focused on overcoming the Type 1 dysfunction, 83,84 this type of dysfunction is not controlled in aquaculture, and species that exhibit Type 1 dysfunctions are either not cultured or reproduction is not controlled, and in those systems, aquaculture uses wild-caught juveniles, for example eels (Anguilla anguilla and A. japonica) and flathead grey mullet (Mugil cephalus). Little research has been conducted on the control of Type 1 dysfunction in LA.…”

“…The rGths have been shown to have higher bioactivity when single-chain structures with an hCG-based linker connect the two subunits produced in mammalian expression systems such as Chinese hamster ovary (CHO) cells that provide the required glycosylation. 96 The rGths have been successfully used in experiments as a single injection of recombinant Lh (rLh) to induce ovulation in fish with a Type-2 dysfunction nearing oocyte maturation, 97,98 and as multiple weekly injections of both recombinant Fsh (rFsh) and rLh, to trigger maturation from the early stages of oogenesis to produce viable ova 83,84 and to trigger the spawning of eggs that ultimately produced millions of larvae (Type 1 dysfunction). 84 These rGths offer excellent potential for reproductive control in aquaculture to provide solutions to both Type-1 and Type-2 reproductive dysfunctions.…”

“…96 The rGths have been successfully used in experiments as a single injection of recombinant Lh (rLh) to induce ovulation in fish with a Type-2 dysfunction nearing oocyte maturation, 97,98 and as multiple weekly injections of both recombinant Fsh (rFsh) and rLh, to trigger maturation from the early stages of oogenesis to produce viable ova 83,84 and to trigger the spawning of eggs that ultimately produced millions of larvae (Type 1 dysfunction). 84 These rGths offer excellent potential for reproductive control in aquaculture to provide solutions to both Type-1 and Type-2 reproductive dysfunctions. Until now, it has been challenging to provide solutions for Type-1 dysfunctions, as the solution requires long treatments that induce the entire oogenesis process from pre-vitellogenesis to spawning of good-quality eggs.…”