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

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.

Impact of sex ratio on the spawning success of zebrafish in the laboratory settings

Zebrafish, Danio rerio belonging to the family Cyprinidae is one of the most important native ornamental model species used in fisheries research globally. The present study was conducted to evaluate the effects of sex ratio on the spawning of zebrafish and to observe the ovarian maturity in the laboratory condition. This experiment was conducted for 12 weeks in the glass aquaria (25×16×26 cm3 in size) and the zebrafish were reared in five different sex ratio treatments like -T1 (1m:1f), T2 (1m:2f), T3 (1m:3f), T4 (2m:1f) and T5 (3m:1f) and the fertilized eggs were collected daily from the aquaria. The results showed that mean number of eggs was found to be highest at T3 (821±67.11) and the average egg lay day interval was 1.9 days which significantly (p<0.05) differ from other treatments. These research findings will provide a guideline to small scale fish farmers, entrepreneurs and hatchery owners to develop the spawning of zebrafish in the laboratory settings with a little investment. It will also provide opportunities to construct zebrafish hatchery and produce commercially zebrafish fry in a large extent. Progressive Agriculture 32 (1): 78-83, 2021

Fore reef location influences spawning success and egg predation in lek-like mating territories of the bird wrasse, Gomphosus varius

Many fish spawn in aggregations, but little is understood about the dynamics governing the success of spawning interactions. Here, we evaluate the influence that location of lek-like mating territories has on spawning interactions of Gomphosus varius. We used direct observations of spawning and egg predation events as well as local population counts to compare the rates of spawning, spawning interruptions, and predation on the eggs of G. varius at Finger Reef, Apra Harbor, Guam. We hypothesized that spawning rates would be highest among seaward locations that facilitate transport of pelagic larvae from reefs and that those territories would subsequently experience higher densities of egg predators, egg predation rates, and spawning interruptions. Male spawning success was highly skewed by mating territory location, with holders of the outer, seaward mating territories being more successful than those males holding territories in the middle and inner areas of the aggregation site. Within the outer territories, male mating success was also skewed by location. Egg predation was observed occasionally and increased linearly with bird wrasse spawning frequency. The population densities of egg predators were distributed equally across the study area. Spawning interruptions occurred most frequently within the inner zone of the spawning aggregation due to greater male-male aggression in intraspecific competition for females and territories. This study provides evidence that reef location influences the spawning success, egg predation rates, and spawning interruption rates of fishes that reproduce using lek-like mating territories.

The importance of thermoperiod for proper gametogenesis and successful egg and sperm production in meagre (Argyrosomus regius) breeders in aquaculture

We examined the effect of constant water temperature throughout the year on gametogenesis, spawning success and egg/sperm/embryo quality in meagre (Argyrosomus regius). Two broodstocks were exposed to simulated natural photoperiod, andeither attenuated seasonal water temperature (SeasT, 16.4 to 19.6ºC) or relatively constant water temperature (CoT, 19.4 ± 0.6ºC).In the spawning period (May), 4 couples per group were induced to spawn with gonadotropin releasing hormone agonist (GnRHa). Gonadal stage of development, sperm quality parameters and plasma levels of sex steroids were evaluated prior to the GnRHa treatment. Spawning success and egg/sperm quality were examined over the following 4 weeks. Constant temperature did not prevent gametogenesis, but exposure to attenuated seasonal water temperature with the inclusion of winter low temperature was beneficial to both sexes. The mean (±SD) diameter of the largest vitellogenic oocytes prior to GnRHa administration was significantly higher in the SeasT compared to the CoT group (598 ± 27 vs 520 ± 17 μm). Testosterone plasma levels in the females were significantly higher in the SeasT group, but all other hormones were similar in both sexes. SeasT females spawned more consistently with higher relative fecundity, and 24-h embryo survival of the produced eggs. A more pronounced negative effect of constant water temperature was observed in males, since CoT males exhibited a spermiation index of 0 prior to GnRHa treatment, the latter clearly having a beneficial effect over the following 4 weeks. The study demonstrated that meagre do undergo gametogenesis to a significant extent even under constant water temperatures during the year. However, a seasonal thermal regime -even an attenuated one- was necessary for the proper development of the gametes, allowing for the successful spawning induction using the established GnRHa induction protocol.

Comparison of Juvenile Feed Protocols on Growth and Spawning in Zebrafish

Over the past 2 decades, zebrafish, Danio rerio, have become a mainstream laboratory animal model, yet zebrafish husbandrypractices remain far from standardized. Feeding protocols play a critical role in the health, wellbeing, and productivity ofzebrafish laboratories, yet they vary significantly between facilities. In this study, we compared our current feeding protocol for juvenile zebrafish (30 dpf to 75 dpf), a 3:1mixture of fish flake and freeze-dried krill fed twice per day with live artemia twice per day (FKA), to a diet of Gemma Micro 300 fed once per day with live artemia once per day (GMA). Our results showed that juvenile EK wild-type zebrafish fed GMA were longer and heavier than juveniles fed FKA. As compared with FKA-fed juveniles, fish fed GMA as juveniles showed better reproductive performance as measured by spawning success, fertilization rate, and clutch size. As adults, fish from both feeding protocols were acclimated to our standard adult feeding protocol, and the long-term effects of juvenile diet were assessed. At 2 y of age, the groups showed no difference in mortality or fecundity. Reproductive performance is a crucial aspect of zebrafish research, as much of the research focuses on the developing embryo. Here we show that switching juvenile zebrafish from a mixture of flake and krill to Gemma Micro 300 improves reproductive performance, even with fewer feedings of live artemia, thus simplifying husbandry practices.

Evidence of prevalent heat stress in Yukon River Chinook salmon

Migrating adult Pacific salmon (Oncorhynchus spp.) are sensitive to warm water (>18 °C), with a range of consequences from decreased spawning success to early mortality. We examined the proportion of Yukon River Chinook salmon (O. tshawytscha) exhibiting evidence of heat stress to assess the potential that high temperatures contribute to freshwater adult mortality in a northern Pacific salmon population. Water temperatures greater than 18 °C have occurred almost annually in the Yukon River and correspond with low population abundance since the 1990s. Using gene transcription products and heat shock protein 70 biomarkers validated by field experiment, we identified heat stress in half of Chinook salmon examined (54%, n = 477) across three mainstem locations and three tributaries in 2016–2017. Biomarkers tracked wide variation in water temperature (14–23 °C) within a tributary. The proportion of salmon with heat stress differed between years at four of the six locations, with more prevalent heat stress in the warmer year. This work demonstrates that warming water temperatures are currently affecting northern populations of Pacific salmon.

Comparative study on spawning success of paradise fish (Macropodus opercularis) using synthetic hormone and natural simulation

Synthetic hormones are widely used for induced breeding with significant successes. This study compared spawning successes in paradise fish (Macropodus opercularis) using synthetic hormone (Ovaprim) and natural simulation in glass tanks (0.3m x 0.6m). The experiment was conducted in two parts using two males and two females brood fish. The weights of the fish were between 4.0 and 5.0g for the males and 5.0 and 6.0g for the females. For the induced spawning, Ovaprim was injected intramuscularly according to the fish body weight after which they were left to spawn. The group on natural spawning were not induced by any hormone. Hatching of the eggs occurred within 48 hours at a temperature of 28.80C. Total number of eggs obtained by artificial and natural breeding were 430 and 322eggs respectively. Percentage fertilization in artificial breeding was 63.26% while 41.93% was recorded in natural breeding. Fry were raised on compounded diet for 6 weeks. Results showed that artificially bred fish had a higher mean weight gain (2.31 g) and survival rate (48.17%) than those from natural breeding having 2.10 g and 44.26% respectively. The results suggest that artificial breeding using synthetic hormone (Ovaprim) yielded better spawning success and survival rate than natural process. Keywords: Paradise fish, natural breeding, hormone, fertilization, survival