Induced oocyte maturation in yellowbelly flounder

doi:10.21203/rs.3.rs-4645497/v1

Download PDF

Research Article

Induced oocyte maturation in yellowbelly flounder

https://doi.org/10.21203/rs.3.rs-4645497/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

Recent interest in developing aquaculture of the endemic New Zealand yellowbelly flounder (YBF) has highlighted the need to develop captive breeding technology for this species. A pilot investigation of induced reproduction was conducted, where twenty-seven female and twelve male wild-caught sexually mature fish were placed into indoor tanks and administered either a sham (saline) or gonadotropin releasing hormone analogue (GnRHa) treatment (50 µg kg-1 or 100 µg kg-1 bw). Ovulation only occurred in GnRHa treated fish. The total number of ovulated fish was low, but the majority of fish treated with 50 µg/kg-1 of GnRHa progressed either into, or through, final oocyte maturation (FOM) to produce hydrated oocytes. Fertilisation rates in excess of 80% were achieved in fish from both the 50 and 100 µg/kg-1 GnRHa treatments, indicating that high quality gametes can be achieved using hormone induced reproduction. In contrast, control fish appeared to arrest oocyte development at FOM suggesting that reproductive dysfunction may occur in wild caught broodstock. With further refinement, induced spawning using GnRHa should be a viable methodology to enhance the hatchery production of YBF.

gonadotropin releasing hormone

flounder

induced reproduction

aquaculture

reproduction

flatfish

New Zealand is characterized by an extensive 15,000 km coastline, however, marine areas allocated for aquaculture total only around 20,000 hectares, with the industry limited to a few key species, primarily Greenshell^™ mussels (Perna canaliculus), Chinook/king salmon (Oncorhynchus tshawytscha), and Pacific oysters (Crassostrea gigas) (Stenton-Dozey et al. 2021). Commercial production of finfish remains underdeveloped and diversification to include new finfish species has been identified to be of critical importance to ensure the expansion of New Zealand’s aquaculture industry is both sustainable and resilient (Camara and Symonds 2014; Valenza-Troubat et al. 2022). Broadening the current understanding of reproduction in novel target finfish species, alongside developing a reliable method for controlling reproduction, are essential steps towards industry diversification.

The temperate yellowbelly flounder (YBF), Rhombosolea leporina, is an endemic right-eyed flatfish found in shallow coastal New Zealand waters. Known as pātiki tōtara in Māori, it is a culturally treasured ‘taonga’ species, targeted by recreational, customary and commercial fishers. Their high flesh quality supports strong local retail prices of approximately NZD $25–35/kg, for whole, gilled and gutted fish. However, coastal YBF populations are believed to be in decline (Moore and McKenzie 2023) and the volume of commercial landings is small (1814 tonnes) (Fisheries New Zealand 2022). Current international and domestic market demand for flatfish indicates potential for commercial aquaculture of this species. Moreover, the cultural value of this species has also highlighted the potential for aquaculture techniques to help conserve wild stocks in coastal rural communities. As such, there is growing interest among these communities to develop land-based aquaculture.

There is currently little information available about captive reproduction of YBF. Captivity-associated reproductive dysfunction is prevalent among marine flatfishes (Order Pleuronectiformes) (Guzmán et al. 2009; Howell et al. 2009; Lim 2016; Mugnier et al. 2000). Such issues are usually characterised by a failure to complete final oocyte maturation (FOM) and ovulation (Zohar and Mylonas 2001). This type of reproductive dysfunction typically relates to a lack of luteinising hormone (LH) release from the pituitary and the subsequent failure to produce the relevant maturation inducing steroids (MIS) in the developing oocyte follicles (García-López et al. 2007; Mylonas et al. 2010).

Here, we report on an initial investigation to induce FOM and ovulation in wild caught YBF under captive conditions. We show that treatment with an exogenous gonadotropin releasing hormone agonist (GnRHa) stimulates FOM to overcome likely reproductive dysfunction. In addition, we update key information regarding its reproductive biology.

Thirty-nine sexually mature YBF were caught at the onset of the breeding season between May and June 2021 using either drag or set nets in the Tauranga Harbour, New Zealand (-37.69°, 176.16°). The fish were anaesthetised (0.6 ml/L^-1, 2-phenoxyethanol, Sigma-Aldrich) and measured for total length (cm) and bodyweight (g) and then individually tagged with plastic floy-tags (Hallprint Pty Ltd.) adjacent to the anterior dorsal fin. Fish were handled in accordance with New Zealand National Animal Ethics Advisory Committee guidelines.

Nine female and four male YBF were assigned to a ‘common-garden’ arrangement in three 1600 L individual recirculating seawater tanks. One of three different treatments of 50 µg/kg^-1 bw and 100 µg/kg^-1 bw of GnRHa (Ovaplant – L, Syndel USA), or a sham of 50 µg/kg^-1 bw Ringer’s solution for marine fish (Setiawan et al. 2016) were injected intraperitoneally into three females in each tank. Fish were fed with fresh Greenshell^™ mussels and mud-crabs (Austrohelice crassa).

Two males in each tank were injected with either 50 µg/kg^-1 bw GnRHa or a sham (Ringer’s solution). Males were checked for expressible milt by gently applying pressure over the abdominal area.

Assessment of ovulation and fertilization

Fish were checked daily for ovulation for the first two weeks following treatment and on sampling days for the last two weeks through visual assessment of abdominal swelling. When this occurred, fish were anaesthetised, and gentle abdominal pressure was applied across the ovary to express ova into a clean, dry plastic bowl. Total egg batch volume was measured in a sterile measuring cylinder and converted to egg quantity using a conversion factor based on ten replicate counts of one millilitre of eggs:

$$Total egg number=number of ml \times \text{3,500}$$

Milt samples were collected by applying gentle abdominal pressure to anaesthetised males after first drying the area surrounding the genital papilla. Sperm motility (10 µl) was qualitatively assessed under a compound microscope (400x magnification) by activation with filtered seawater (10 µl). Fresh batches of eggs were fertilised using sperm that showed sustained vigorous motility for at least 60 seconds. Eggs were dry fertilised using a volumetric milt to egg ratio of 1:100. Egg viability $(volume of buoyant eggs-total egg volume \times 100)$ was assessed after 25 minutes. Sub-samples of 100 eggs (n = 3) were examined at the 4–8 cell stage to determine fertilisation rate (%).

Histological and fresh oocyte analysis

Ovarian development was monitored during the course of the experiment through the collection of fresh oocytes using repeat ovarian biopsies on days; 0 (time of injection), 3, 7, 14, 21 and 28. A failure of the catheter on the first day meant that some of the initial biopsies could not be obtained, however daily macroscopic inspection of the fish until subsequent biopsy (day 3) indicated that none of these unbiopsied fish were likely to have completed final oocyte maturation (FOM). Biopsies were obtained following anaesthetisation through gentle aspiration of the ovary using a flexible plastic catheter (2.0 mm outer diameter). A portion of these samples were transferred to a petri dish and immediately dispersed in Sera’s clearing solution (ethanol:formalin:acetic acid, 6:3:1 v/v) to allow identification of the germinal vesicle. They were then photographed (Olympus EP50) under a stereo microscope (Olympus SZ61) along with a 0.01 mm staging micrometer. Mean fresh oocyte diameter was measured digitally (ImageJ) using bisecting lines across the longest and shortest axis of each oocyte. Different developmental stages of fresh oocytes were identified according to their morphometric qualities. These stages were verified against histological samples from the same biopsy samples (Fig. 1).

The remaining oocytes from each sample were fixed in 10% neutral buffered formalin for 24 hours followed by transfer to 70% ethanol and later processed for standard paraffin embedded sectioning (3–4 µm) and stained with haematoxylin and eosin. These ovarian histology samples were examined using light microscopy (Olympus CX23) and classified into the following developmental stages according to the leading cohort of oocytes: 1) primary (previtellogenic), 2) secondary (a) early and (b) late vitellogenic, or 3.) tertiary (a) early (up to germinal vesicle migration (GVM)/breakdown (GVBD)) and (b) late (hydrated) maturation.

Data analysis

Data analysis was completed in R (version 4.04). Barnard’s exact test was used to test whether the development of maturing and hydrated oocytes as well as mortality were independent between GnRHa and control treatments. Treatment-related differences in female body weight was determined by one-way ANOVA and homogeneity of variance and normality assessed using Levene’s test and the Shapiro-Wilk test, respectively.

Initial female body weight ranged between 254–829 g and did not differ among treatments. Sixteen mortalities occurred in the latter stages of the experiment with no significant relationship to treatment. Close inspection indicated the presence of an ectopic fungal infection.

Histology and ovarian development

All fish contained oocytes that were at least vitellogenic at the initiation of the study with the exception of six fish which contained primary oocytes (Fig. 2). These previtellogenic fish occurred evenly across treatments and each contained recent atretic, later-stage oocytes. A similar number of fish were found to have ovaries in the early stages of maturation (lipid coalescence). Despite there being equal numbers of these peri-maturational fish in each treatment, only the 50 µg/kg GnRHa individuals continued to develop through FOM.

Ovarian development generally remained static or continued to regress over time in control and 100 µg/kg GnRHa fish. In contrast, the 50 µg/kg GnRHa treated fish either entered FOM (Fig. 3a) or progressed to later maturational stages (p < 0.05, t = 2.160) such as GVM (Fig. 3b), GVBD (Fig. 3c) or hydration (p < 0.05, t = 2.415) (Fig. 3d) (Fig. 4). There was no statistical difference in the number of 100 µg/kg GnRHa fish entering or progressing through these maturational stages compared to controls. At least three of the 100 µg/kg GnRHa fish had ovaries that progressed from containing secondary oocytes to GVM between days 14 to 28 post treatment.

Ovulation, egg fertilisation and milt production

Peri-ovulatory fish were evident by the presence of dorso-ventral swelling demarcating the outline of the ovaries. Ovulation appeared to occur in the scotophase, with gravid fish sometimes proving difficult to strip prior to evening despite the presence of hydrated oocytes. In these instances, free-flowing ovulated eggs were easily obtained the following morning. Ovulation was only observed in GnRHa treated fish (50 µg/kg, n = 3; 100 µg/kg, n = 1), with a total of seven batches of eggs collected (Table. I). Three fish ovulated twice with a periodicity of approximately 3 days between ovulations. The mean latency (time to ovulation) following GnRHa administration was 4 ± 0.6 days for the 50 µg/kg GnRHa treated fish compared to 28 days observed in a single 100 µg/kg GnRHa fish. Greater mean weighted fecundity (100g^-1 bw) was observed in 50 µg/kg GnRHa treated fish compared to 100 µg/kg GnRHa fish. Fecundity and fertilisation rates ranged from 0–84%, although fertilisation rates up to 80% or greater were recorded in both GnRHa treatments.

Milt collection from male fish was low (approximately 0–500 µl) and there did not appear to be an effect of GnRHa treatment on the expressible milt volume.

Table. I Effect of GnRHa treatment on mean weighted total fecundity, egg quality and latency in sexually mature yellowbelly flounder. * Data not recorded

Treatment	Mean fecundity (100 g BW)	Fertilization (%)	Egg viability (%)	Latency (days)
Control	-	-	-	-
50 µg/kg GnRHa	33,915 ± 7435	0–84	80.7 ± 7.7	3–5
Second ovulation	10,854 ± 4047	0	2 ± 2	7–8
100 µg/kg GnRHa	17,877	80	-*	28
Second ovulation	-*	-*	-*	31

The development of a new candidate species for aquaculture requires control of the breeding cycle to ensure a consistent supply of fertile gametes. This initial investigation of captive reproduction in wild caught female YBF indicates that treatment with exogenous GnRHa successfully activates the reproductive axis in comparison to sham treated, control fish.

Only GnRHa treated fish were found with hydrated oocytes or observed to have ovulated. Injection with at least 50 µg/kg GnRHa stimulates FOM in wild caught female YBF. Interestingly, a higher dose of 100 µg/kg of GnRHa did not significantly stimulate FOM. Latency in the single fish which did ovulate in this higher dosage group, was considerably longer (28 days) compared to those in the 50 µg/kg GnRHa treatment (less than 6 days). While fertilisation rates were highly variable, both treatment groups yielded egg batches with ≥ 80% fertilisation, in contrast with low fertilization rates reported from hormonally induced spawning in some flatfish, e.g. southern flounder (Paralichthys lethostigma) (Watanabe et al. 2001; Wright-Moore et al, 2019). The reason for the increased latency of the higher GnRHa dose is unknown but could relate to temporary desensitisation of the GnRH receptors (GnRH-r) on the pituitary gonadotropic cells. Our recent work shows that pituitary luteinising hormone beta-subunit (lhb) expression is upregulated within 24 hours in YBF following injection with either 25 µg/kg or 50 µg/kg of GnRHa but not with 100 µg/kg GnRHa (unpublished data). Continuous exposure to GnRH has been demonstrated to desensitise pituitary LH release in both goldfish (Carassius auratus) and tilapia hybrids (Oreochromis niloticus x O. aureus). Levavi-Sivan et al. (2004) found that elevated doses of GnRHa dramatically decreased GnRH-r mRNA levels in comparison to lower doses in tilapia although plasma LH was not affected. These observations pose intriguing physiological questions with a view to the optimal dosage of GnRHa in YBF.

Hormonal therapy often needs fine tuning to develop an optimised protocol. While injection with 50 µg/kg GnRHa stimulated the progression of oocytes into advanced stages of FOM (GVBD and hydration), this did not necessarily result in ovulation. Studies of induced reproduction in other species of fish have also resulted in a portion of individuals ovulating following GnRHa treatment (Berlinsky et al. 1997; Poortenaar and Pankhurst 2000; Setiawan et al. 2016). The efficacy of exogenous hormone treatment is subject to a number of influencing factors, such as stage of ovarian development, presence of endogenous hormonal inhibition, as well as the delivery method of the therapeutant and dosage (Chang and Peter 1983; Cerdà et al. 1997; Forniés et al. 2001; Zohar and Mylonas 2001; Levavi-Sivan et al. 2004). The identification of an optimal dosage is critical to maximise ovulation in YBF and further refinement is required. The fact that some hormone-treated fish failed to enter FOM, may reflect insufficient ovarian development at the time of GnRHa administration (Berlinsky et al. 1997; Mugnier et al. 2000; Wright-Moore et al. 2019). The presence of both PVO and late stage atretic oocytes in many of these fish suggests that they were either post-spawned or had entered stress-related atresia, following capture. Breeding in wild YBF is reported to occur between early winter and early summer (June – December) (Colman 1973). It is yet to be reported as to whether individual fish spawn throughout this period or at specific times within this seasonal window. In the latter scenario, it is likely that any given group of wild caught fish will contain at least some individuals that are not in breeding condition. Based on the initial size of oocytes in the individuals that successfully responded to treatment; it is recommended that GnRHa is administered when oocytes are approximately 300 µm diameter. Oocytes of this size are likely to correspond to late-vitellogenic or early maturational stages of ovarian development. This is when FOM is typically induced via LH mediated stimulation of the MIS (Nagahama 1994; Nagahama and Yamashita 2008).

The failure of control fish to complete FOM to yield hydrated or ovulated oocytes suggests that wild caught YBF are, at least initially, prone to reproductive dysfunction in captivity. This is a common result of stress which has been observed in other wild caught broodstock fish (Corriero et al. 2021; Imanaga et al. 2014; Mehdi and Ehsan 2011). Failure to enter FOM is one of the most common forms of reproductive dysfunction in captive fish and typically responds to GnRHa treatment (Lim 2016; Prat et al. 2001; Rosenfeld et al. 2012). While hormonal interventions have been associated with reduced gamete quality in some fish (Mugnier et al. 2000; Forniés et al. 2001; Garber et al. 2009; Setiawan et al. 2016), high fertilization rates (> 80%) were achieved in this study indicating that treatment with 50–100 µg/kg GnRHa can yield good quality egg batches.

Milt production in males may prove to be a limiting factor for the development of artificial fertilisation protocols for YBF. Comparatively small volumes (< 0.5 ml) of milt were able to be collected from individuals in this study and production did not appear to be greatly enhanced with GnRHa treatment. It is important to note that this observation is anecdotal as the study primarily focused on induced reproduction in female YBF. Pankhurst and Poortenaar (2000) recorded similar volumes of milt in greenback flounder (Rhombosolea taparina) and concluded that human choriogenic hormone (hCG) and GnRHa both increased milt volume relative to saline controls. Low efficacy of GnRHa treatment on milt production was reported in male summer flounder (Paralichthys dentatus; Berlinsky et al. 1997) and Senegalese sole (Solea senegalensis; Guzmán et al. 2010). Evidence indicates that dopamine inhibition within the reproductive axis may suppress GnRHa efficacy in male Senegalese sole (Guzmán et al. 2010). The co-administration of a dopamine antagonist and GnRHa was effective at increasing spermiation and milt volume in Senegalese sole (Guzmán et al. 2011). Methodologies to increase expressible milt volumes in YBF may warrant further investigation to avoid future bottlenecks in hatchery production.

Reproductive behaviours appeared to be absent during the study and there was no evidence of spontaneous spawning occurring despite some of the GnRHa treated fish having ovulated. Similar results occur in captive Atlantic halibut (Hippoglossus hippoglossus) where hand-stripping is necessary (Skaalsvik et al. 2015). This may relate to the requirement of specific husbandry or environmental conditions. Pankhurst and Fitzgibbon (2006) found that captive greenback flounder undergo spontaneous spawning in the mid-water column when held in a low disturbance environment at reduced densities (~ 1kg/m³). Broodstock fish in the current study experienced regular handling disturbance and were held at greater stocking densities. While wild YBF are often caught on shallow mudflats in less than one metre of water, spawning typically occurs at depths of 12-30m (Colman 1973; Smith et al. 1999). The depth of the tanks used in the present study (0.6 m) may have been inadequate to support natural courtship and spawning. Future work should consider adapting the tank environment to encourage natural reproduction.

Few studies have focused on the reproductive biology of YBF although previous reports state that they seasonally spawn a single batch of eggs (Colman 1973; Mutoro 2001). The existence of distinct cohorts of oocytes at various stages of development (including vitellogenic and FOM) as observed in this study, suggests a different reproductive strategy. Moreover, the observation that some fish ovulated more than once, strongly indicates that YBF are multiple group synchronous batch spawners as suggested by Koverman (2018). A similar pattern of ovarian development also exists in greenback flounder (Poortenaar and Pankhurst, 2000) as well as many other temperate flatfish (Berlinsky et al. 1997; Earl 2014; Lim 2016; Poortenaar et al. 2001; Tingaud-Sequeira et al. 2009).

In summary, this study is one of the first reports on captive reproduction and the related reproductive biology of YBF. Based on gonadal histology and the observed repeat ovulations these fish should be considered multiple group synchronous batch spawners. Our work indicates that female YBF with oocytes over 300 µm diameter can be induced to enter FOM with a GnRH agonist treatment at 50 µg/kg bodyweight. While further refinement of dosage would be advantageous, GnRHa should be a viable therapeutant for inducing ovulation in YBF.

Acknowledgements

The authors wish to acknowledge the engagement and discussion from members of Ngāi Te Rangi, Ngāti Ranginui, Ngāti Pūkenga and Whakatōhea in regard to this project. In addition, Kevin Green, Samantha Carter, Hana Mason, Mischa McCauley, Eva Patai and Niki de Baugh assisted with fish capture and husbandry during the study. Toi Ohomai Institute of Technology and the associated research committee generously granted access to research lab facilities.

Funding

This work was supported in full by the Sustainable Seas National Science Challenge, established by the Ministry of Business, Innovation and Enterprise, New Zealand. Project number 2.16.

Competing interests

The authors have no relevant non-financial interests to disclose. Full research funding was provided by Sustainable Seas National Science Challenge, established by the Ministry of Business, Innovation and Enterprise, New Zealand. Project number 2.16.

Author contributions

SM conceived the study and secured the funding. All authors contributed to the experimental design and experimental work. All authors conducted the statistical analysis. BE wrote the first draft and all authors contributed to the editing and finalising of the article.

Ethics approval

All procedures involving animals were in compliance with the New Zealand Animal Welfare Act 1999, and ethical approval was granted by the Toi Ohomai Institute of Technology Animal Ethics Committee (No. AEC 2021.002). Wild capture of yellowbelly flounder was approved under a New Zealand Ministry for Primary Industries fisheries special permit.

Data availability statement

Data is available in article Supplementary Information and raw data is available on request from the authors.

Berlinsky DL, William KV, Hodson RG, Sullivan CV (1997) Hormone induced spawning of summer flounder Paralichthys dentatus. Journal of the World Aquaculture Society 28(1):79-86
Camara M, Symonds J (2014) Genetic improvement of New Zealand aquaculture species: Programmes, progress and prospects. New Zealand Journal of Marine and Freshwater Research 48(3):466-491
Chang JP, Peter RE (1983) Effects of pimozide and des Gly10, [D-Ala6] luteinizing hormone-releasing hormone ethylamide on serum gonadotropin concentrations, germinal vesicle migration, and ovulation in female goldfish, Carassius auratus. General and Comparative Endocrinology 52(1):30-37
Cerdà J, Selman K, Hsiao SM, Wallace RA (1997) Evidence for the differential regulation of ovarian follicle responsiveness to human chorionic gonadotropin in vitro in a serranid teleost, Centropristis striata. Aquaculture 159(1–2):143-157.
Colman JA (1973) Spawning and fecundity of two flounder species in the Hauraki gulf, New Zealand. New Zealand Journal of Marine and Freshwater Research 7(1-2):21-43.
Corriero A, Zupa R, Mylonas CC, Passantino L (2021) Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries. Journal of Fish Diseases 44(9):1271-1291.
Earl J (2014) Population biology and ecology of the greenback flounder (Rhombosolea tapirina) in the Coorong estuary, South Australia. Dissertation, Flinders University.
Fisheries New Zealand (2022) Fisheries Assessment Plenary, May 2022: stock assessments and stock status. Wellington (New Zealand): Complied by the Fisheries Science and Information Group, Fisheries New Zealand
Forniés M, Mañanós E, Carrillo M, Rocha A, Laureau S, Mylonas CC, Zohar Y, Zanuy S (2001) Spawning induction of individual European sea bass females (Dicentrarchus labrax) using different GnRHa-delivery systems. Aquaculture 202(3–4):221-234
Garber AF, Fordham SE, Symonds JE, Trippel EA, Berlinsky DL (2009) Hormonal induction of ovulation and spermiation in Atlantic cod (Gadus morhua). Aquaculture 296(1–2):179-183
García-López Á, Couto E, Canario AV, Sarasquete C, Martínez-Rodríguez G (2007) Ovarian development and plasma sex steroid levels in cultured female Senegalese sole Solea senegalensis. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 146(3):342-354
Guzmán JM, Ramos J, Mylonas CC, Mañanós EL (2009) Spawning performance and plasma levels of GnRHa and sex steroids in cultured female Senegalese sole (Solea senegalensis) treated with different GnRHa-delivery systems. Aquaculture 291(3-4): 200-209
Guzmán JM, Cal R, García-López A, Chereguini O, Kight K, Olmedo M, Sarasquete C, Mylonas CC, Peleteiro JB, Zohar Y, Mañanós EL (2011) Effects of in vivo treatment with the dopamine antagonist pimozide and gonadotropin-releasing hormone agonist (GnRHa) on the reproductive axis of Senegalese sole (Solea senegalensis). Comp Biochem Physiol A Mol Integr Physiol 158(2):235-45
Howell B, Conceição LE, Prickett R, Cañavate JP, Mañanós EL (2009) Sole farming: nearly there but not quite? A report of 4th workshop on the cultivation of soles. Aquaculture Europe 34:24-27
Imanaga Y, Nyuji M, Amano M, Takahashi A, Kitano H, Yamaguchi A, Matsuyama M (2014) Characterization of gonadotropin-releasing hormone and gonadotropin in jack mackerel (Trachurus japonicus): comparative gene expression analysis with respect to reproductive dysfunction in captive and wild fish. Aquaculture 428:226-235
Koverman R (2018) Reproductive biology of yellowbelly flounder Rhombosolea leporina (Günther, 1862) and Rhombosolea spp. Dissertation, University of Waikato.
Levavi-Sivan B, Safarian H, Rosenfeld H, Elizur A, Avitan, A (2004) Regulation of gonadotropin releasing hormone (GnRH)-receptor gene expression in tilapia: Effect of GnRH and dopamine. Biology of Reproduction 70(6):1545-1551
Lim HK (2016) Effect of exogenous hormones on ovulation and gonadal steroid plasma levels in starry flounder, Platichthys stellatus. Aquaculture International 24(4):1061-1071
Mehdi Y, Ehsan S (2011) A review of the control of reproduction and hormonal manipulations in finfish species. African Journal of Agricultural Research 6(7):1643-1650
Moore B, McKenzie J (2023) Associations between environmental variables and flatfish catch rates in Manukau Harbour and Kaipara Harbour. Wellington: Fisheries New Zealand. New Zealand Fisheries Assessment Report 2023/20
Mugnier C, Guennoc M, Lebegue E, Fostier A, Breton B (2000) Induction and synchronisation of spawning in cultivated turbot (Scophthalmus maximus L.) broodstock by implantation of a sustained-release GnRH-a pellet. Aquaculture 181(3-4):241-255
Mutoro DB (2001) Life of a flatfish, the yellowbelly flounder, Rhombosolea leporina Günther, 1873, in Auckland's sheltered waters. Dissertation, University of Auckland
Mylonas CC, Fostier A, Zanuy S (2010) Broodstock management and hormonal manipulations of fish reproduction. General and Comparative Endocrinology 165(3):516-534
Nagahama Y (1994) Endocrine regulation of gametogenesis in fish. The International Journal of Developmental Biology 38(2):217-229
Nagahama Y, Yamashita M (2008) Regulation of oocyte maturation in fish. Development, Growth & Differentiation 50:195-219
Norberg B, Valkner V, Huse J, Karlsen I, Lero G (1991) Ovulatory rhythms and egg viability in the Atlantic halibut (Hippoglossus hippoglossus). Aquaculture 97(4):365-371
Pankhurst N, Fitzgibbon Q (2006) Characteristics of spawning behaviour in cultured greenback flounder Rhombosolea tapirina. Aquaculture 253(1-4):279-289
Poortenaar C, Hickman R, Tait M, Giambartolomei F (2001) Seasonal changes in ovarian activity of New Zealand turbot (Colistium nudipinnis) and brill (C. guntheri). New Zealand Journal of Marine and Freshwater Research 35(3):521-529
Poortenaar CW, Pankhurst NW (2000) Effect of luteinising hormone‐releasing hormone analogue and human chorionic gonadotropin on ovulation, plasma and ovarian levels of gonadal steroids in greenback flounder Rhombosolea tapirina. Journal of the World Aquaculture Society 31(2):175-185
Prat F, Zanuy S, Carrillo M (2001) Effect of gonadotropin-releasing hormone analogue (GnRHa) and pimozide on plasma levels of sex steroids and ovarian development in sea bass (Dicentrarchus labrax L.). Aquaculture 198(3-4):325-338
Rosenfeld H, Mylonas CC, Bridges CR, Heinisch G, Corriero A, Vassallo-Aguis R, Medina A, Belmonte A, Garcia A, De la Gándara F (2012) GnRHa-mediated stimulation of the reproductive endocrine axis in captive Atlantic bluefin tuna, Thunnus thynnus. General and Comparative Endocrinology 175(1):55-64
Sampaio LA, Robaldo RB, Bianchini A (2008) Hormone‐induced ovulation, natural spawning and larviculture of Brazilian flounder Paralichthys orbignyanus (Valenciennes, 1839). Aquaculture Research 39(7):712-717
Setiawan A, Muncaster S, Pether S, King A, Irvine G, Lokman P, Symonds J (2016) The effects of gonadotropin-releasing hormone analog on yellowtail kingfish Seriola lalandi (Valenciennes, 1833) spawning and egg quality. Aquaculture Reports 4:1-9
Skaalsvik TH, Bolla SL, Thornqvist PO, Babiak I (2015) Quantitative characteristics of Atlantic halibut (Hippoglossus hippoglossus L.) egg quality throughout the reproductive season. Theriogenology 83(1):38-47
Smith TI, McVey DC, Jenkins WE, Denson MR, Heyward LD, Sullivan CV, Berlinsky DL (1999) Broodstock management and spawning of southern flounder, Paralichthys lethostigma. Aquaculture 176(1-2):87-99
Stenton-Dozey JM, Heath P, Ren JS, Zamora LN (2021) New Zealand aquaculture industry: Research, opportunities and constraints for integrative multitrophic farming. New Zealand Journal of Marine and Freshwater Research 55(2):265-285
Tingaud-Sequeira A, Chauvigné F, Lozano J, Agulleiro MJ, Asensio E, Cerdà J (2009) New insights into molecular pathways associated with flatfish ovarian development and atresia revealed by transcriptional analysis. BMC Genomics 10(1):1-25
Valenza‐Troubat N, Hilario E, Montanari S, Morrison‐Whittle P, Ashton D, Ritchie P, Wellenreuther M (2022) Evaluating new species for aquaculture: A genomic dissection of growth in the New Zealand silver trevally (Pseudocaranx georgianus). Evolutionary Applications 15(4):591-602
Walker PJ, Winton JR (2010) Emerging viral diseases of fish and shrimp. Veterinary Research 41(6):51
Watanabe WO, Carroll PM, Daniels HV (2001) Sustained, natural spawning of southern flounder Paralichthys lethostigma under an extended photothermal regime. Journal of the World Aquaculture Society 32(2):153-166
Wendelaar Bonga SE (1997) The stress response in fish. Physiological Reviews 77(3):591-625
Wright-Moore WD, Watanabe WO, Bourdelais AJ, Alam M, Rezek TC, Carroll PM, Woolridge CA (2019) Spawning performance and egg quality of wild-caught and first generation southern flounder Paralichthys lethostigma broodstock induced with piscine and mammalian GnRH analogs. Aquaculture 506:367-379
Zohar Y, Mylonas CC (2001) Endocrine manipulations of spawning in cultured fish: From hormones to genes. Reproductive Biotechnology in Finfish Aquaculture 197:99-136

Competing interest reported. The authors have no relevant non-financial interests to disclose. Full research funding was provided by Sustainable Seas National Science Challenge, established by the Ministry of Business, Innovation and Enterprise, New Zealand. Project number 2.16.

Supplementaryinformationdata.xlsx

Download PDF

Reviews received at journal
30 Jul, 2024
Reviewers agreed at journal
01 Jul, 2024
Reviewers agreed at journal
01 Jul, 2024
Reviewers invited by journal
28 Jun, 2024
Editor assigned by journal
28 Jun, 2024
Submission checks completed at journal
27 Jun, 2024
First submitted to journal
26 Jun, 2024

You are reading this latest preprint version

Induced oocyte maturation in yellowbelly flounder

Status:

Version 1

Abstract

Figures

Introduction

Materials and Methods

Assessment of ovulation and fertilization

Histological and fresh oocyte analysis

Data analysis

Results

Histology and ovarian development

Discussion

Conclusion

Declarations

Acknowledgements

Funding

Competing interests

Author contributions

Ethics approval

Data availability statement

References

Additional Declarations

Supplementary Files

Status:

Version 1