Providing recombinant gonadotropin-based therapies that induce complete oogenesis and produce viable larvae from an immature teleost, flathead grey mullet (Mugil cephalus)

Abstract

Under intensive captive conditions, wild-caught flathead grey mullet (Mugil cephalus) 12 females remain arrested at early gonad development and males do not produce sperm. With the aim to induce gametogenesis and obtain fertilized eggs, adult female and male 14 grey mullet were treated with M. cephalus single-chain recombinant gonadotropins (rGths), follicle-stimulating (rFsh) and luteinizing (rLh) hormones. In Experiment 1, a 16 weekly dose of rFsh (15 µg kg -1 ) significantly (P < 0.001) increased plasma concentration of 17β-estradiol in females and induced oocyte growth up to a maximum diameter of 425 18 ± 19 µm after 9 weeks of treatment. In males, spermiogenesis (> 75% motile spermatozoa) was induced after 5 weeks to produce low quantities (29.3 ± 6.1 µL) of 20 viscous sperm. However, the application of therapies based on human chorionic gonadotropin (hCG) or gonadotropin releasing hormone agonist (GnRHa) were 22 ineffective to complete oocyte maturation. In Experiment 2, fish were treated with weekly injections of both rFsh and rLh at different doses (from 2.5 to 12 µg kg -1 ). Oocyte 24 diameter reached 609 ± 5 µm prior to oocyte maturation and ovulation, which was induced with 30 µg kg -1 of rLh and 40 mg kg -1 of progesterone. Higher quantities of good 26 quality sperm (92.7 ± 24.7 µL) were obtained after rLh treatment of males and used to fertilise the eggs. Although the percentage of fertilisation was low (0.4 %), these eggs 28 were able to produce viable larvae (71% hatching rate). In comparison, control groups remained arrested as immature fish. The study demonstrated that both rGths are effective 30 to induce the entire process of gametogenesis in sexually immature male and female grey mullet, which confirmed the central roles of the Gths in teleost gametogenesis. This 32 advance provides the bases of a therapy for the use in the aquaculture of teleosts of commercial interest or the conservation of endangered species. 34 42 positive attributes of grey mullet culture have made this species a suitable option for aquaculture. Grey mullet has fast growth (0.75 -1 kg per year) [2], does not require 44 dietary fish meal and oil and can be reared in a wide range of salinities and culture systems including polyculture [3]. In addition, the final product marketed in various forms has 46 good texture, taste [4] and is an excellent source of omega-3 essential fatty acids [5].Although this species has a long history of culture, it exhibits different degrees of 48 reproductive dysfunctions in both genders under captive conditions. These dysfunctions have limited the possibility to close the life cycle and, thus, culture has been based on the 50 capture of wild juveniles [4] or induced spawning of wild breeders [6 -10]. Two types of reproductive dysfunction have been described and can be placed in two categories; arrest 52 in the late stages or early stages of gametogenesis. Arrest in late stages of gametogenesis (maturation and ovulation) has been observed in recently caught wild mullet or wild 54 mullet...

Characterization of the different behaviours exhibited by juvenile grey mullet (Mugil cephalus) under rearing conditions

“…The economic importance of Mugil is based on its consumption and its cost varies from one region to another, relying on several factors; for example, female’s grey mullet gonads, also known as caviar or bottarga, could reach 65 € per kg in the European markets (Aldana, 2015; Rodríguez, 2018). Therefore, significant advances have been made on nutrition, growth, larval culture and reproduction of individuals reared in captivity (Martínez et al ., 2019; Talukdar et al ., 2020; Besbes et al ., 2020; Ramos-Júdez et al ., 2021). Furthermore, several studies have demonstrated that grey mullet can also be an adequate candidate species for mariculture which can contribute to food production and the reduction of fishing impact (Saleh, 2008; Robles & Mylonas, 2017).…”