Elsevier

Aquaculture

Volume 533, 25 February 2021, 736025
Aquaculture

Methods of domestic striped bass (Morone saxatilis) spawning that do not require the use of any hormone induction

https://doi.org/10.1016/j.aquaculture.2020.736025Get rights and content

Highlights

  • Striped bass are able to batch spawn after photothermal and salinity conditioning

  • Batch spawning striped bass does not require any exogenous hormone treatments

  • At least ten striped bass of each sex are required to elicit batch spawning behavior

  • The batch spawning method is commercially scalable for striped bass production

  • Striped bass are promiscuous and will reproduce with multiple partners

Abstract

Nineteen batch spawning trials were conducted using 5th and 6th generation domestic striped bass (Morone saxatilis) to demonstrate the ability of these fish to volitionally spawn in large tanks to produce larvae using only photothermal and salinity conditioning. The findings described are the first report of multiple striped bass successfully batch spawning in captivity without exogenous hormone administration. The results of these trials indicate that an approximately 1:1 ratio of female to male striped bass in a single batch spawning unit is more favorable for production, that a minimum of at least 10 fish of each sex is required to elicit this particular spawning behavior, and that using 25 fish of each sex will yield commercially scalable larval production. This batch spawning method has been employed to effectively and consistently spawn over half of the female striped bass in the National Program for Genetic Improvement and Selective Breeding for the Hybrid Striped Bass Industry (N = 202 of 334 female fish over five years) to produce 44,608,181 swim-up larvae (26.6% hatching rate). Microsatellite genotyping and parentage assignment demonstrates that females will reproduce with between 2 and 18 males and that males will reproduce with between 1 and 6 females. Moreover, the effective broodstock size (Nb) of these batch spawning units is 33 and when accounting for multiple partners and unequal family sizes (Nbv) is 28. Lastly, the reported results include the successful spawning of female striped bass staged at and beyond 15 Bayless hours, or those that would have previously been considered ineligible for spawning even with the use of exogenous hormone treatment.

Introduction

Farming of sunshine bass (hybrid bass produced from a cross of female white bass Morone chrysops x male striped bass M. saxatilis) is presently the fourth largest finfish aquaculture industry in the United States, behind only catfish, salmon, and trout, with over 14 million pounds produced annually at a farm-gate value of approximately $50 million USD (Reading et al., 2018; USDA, 2019). It is estimated that as much as 90% of the sunshine bass raised in the United States from 2015 to 2019 were produced using domesticated male striped bass broodstock from the National Program for Genetic Improvement and Selective Breeding for the Hybrid Striped Bass Industry housed at the North Carolina State University Pamlico Aquaculture Field Laboratory (Aurora, NC, USA). Fish from this program are bred annually and male striped bass broodstock are disseminated to fingerling producers throughout the country. Optimizing domestic striped bass spawning would greatly enhance the capacity and efficiency to produce broodstock for the hybrid striped bass industry, may open the door to tank spawning production of hybrid striped bass or true-breeding hybrid striped bass, and will provide a means for consistent larval fish (fry) production for an emergent striped bass aquaculture or mariculture industry (McCraren, 1984; Hallerman, 1994; Reading et al., 2018). Additionally, the value of domestic striped bass broodstock from The National Breeding Program to the industry may increase overall if they are shown to spawn under greatly simplified culture conditions compared to traditional wild-captured broodstock (Hodson et al., 1999; Woods III, 2001; Garber and Sullivan, 2006).

The current standard method of spawning striped bass is to tank or strip spawn males and females from wild and domestic stocks that have been treated with gonadotropin releasing hormone analog (GnRHa) implants and/or human chorionic gonadotropin (hCG, Chorulon) injections (Harrell et al., 1990; Hodson and Sullivan, 1993; Woods III and Sullivan, 1993; Harrell, 1997; Andersen et al., 2020). Treatment with these exogenous hormone compounds has historically been considered mandatory to induce gamete maturation in female striped bass and to prolong spermiation and milt hydration in male striped bass held in captivity (Hodson and Sullivan, 1993; Grizzle et al., 1995; Mylonas et al., 1996; Frankel et al., 2013; Andersen et al., 2020). Although reliance on hormones for commercial aquaculture foodfish production may be useful, there are several considerations such as cost, regulations, handling stress, and public concern (Smith, 1989; Hodson and Sullivan, 1993; Andersen et al., 2020).

We recently reported the first observations of untreated, domestic striped bass females volitionally spawning in the presence of a hormone-treated female and several males (three to five per tank) to successfully yield fertilized eggs and subsequent fry (Andersen et al., 2020). In this “pace-set” spawning approach, the female striped bass treated with exogenous hormone compound (GnRHa or hCG) is thought to prompt the spawning behavior (i.e., ovulation and release of eggs) of the untreated females and therefore set the pace, or occurrence, of spawning (Andersen et al., 2020). In the majority of those trials (87.5%), the hormone-treated female volitionally spawned, as expected, and in half of the trials this was followed by volitional spawning of the untreated females (Andersen et al., 2020). Prior to the findings reported by Andersen et al. (2020), there was only one published record of a captive female striped bass volitionally releasing eggs in a tank without being treated with exogenous hormone compound (Woods III et al., 1990). The reported findings on pace-set spawning suggest that domestic female striped bass do not necessarily require treatment with hormone compounds and may be able to spawn in large groups, or “batches.” The possibility of this is further validated by our observation of untreated domestic female striped bass volitionally releasing their eggs when in the presence of males during routine photothermal conditioning, although the fertilities of these spawns were not verified (R.W. Clark and M.S. Hopper, unpublished data).

Here, we evaluate the efficacy of eliminating traditional hormone induction methods from striped bass spawning protocols (Harrell et al., 1990; Harrell, 1997) by manipulating photothermal and salinity parameters to batch spawn between sixteen and seventy-four mixed sex fish in a single tank. Nineteen batch spawning trials were conducted with the following objectives: (1) to determine if domestic female striped bass are capable of volitionally batch spawning en masse without hormone treatment (nineteen trials); (2) to determine the optimal sex ratio of domestic striped bass broodstock females and males that results in the most effective spawning success (seven trials); (3) to determine if batch spawning of domestic striped bass is possible without inducing male striped bass with hCG (four trials); (4) to explore the minimum number of domestic striped bass required to elicit hormone-free batch spawning in captivity (four trials); (5) to commercially scale hormone-free batch spawning of domestic striped bass (four trials); (6) to gain insight into the reproductive success of males and females using microsatellite genotyping (one trial); and lastly, (7) to observe the spawning activity of females of different known oocyte stages measured in Bayless hours (five trials) (Bayless, 1972; Rees and Harrell, 1990; Watson, 1992).

Section snippets

Experimental animals

All research was performed under the protocol approved by the Institutional Animal Care and Use Committee of North Carolina State University (Protocol numbers 10-042-A and 19-065-O). The study was carried out in accordance with the recommendations located in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health (NRC, 1996).

All domestic striped bass described here are a part of the National Program for Genetic Improvement and Selective Breeding for the Hybrid

Results

A total of 202 female striped bass of the 334 included in all of the trials (60.5% of all female fish) were found to have participated in spawning by the conclusion of all trials (Table 1), demonstrating that female striped bass can spawn volitionally without hormone induction. The mean oocyte stage for the striped bass females sampled for ovarian biopsy was 13.4 ± 0.82 Bayless hours. Spawns were observed in all but one of the trials (Trial 12), which included only eight fish of each sex (i.e.,

Discussion

The results of the eighteen successful batch spawning trials are the first reported confirmation that domestic striped bass females and males are able to volitionally spawn in large batch spawning tanks (7047 L - 31,139 L) and yield appreciable fry production after only photothermal and salinity conditioning. All attempts to spawn female striped bass in captivity without the use of exogenous hormones prior to the reported success by Andersen et al. (2020) had been met with marginal success or

Declaration of Competing Interest

The authors declare that there is no conflict of interest in this work.

Acknowledgements

The authors thank Dr. Craig V. Sullivan for his longstanding contributions to the National Program for Genetic Improvement and Selective Breeding for the Hybrid Striped Bass Industry. The authors would also like to thank B.J. Runde for providing graphical consultation. This work was supported by funding provided from the following sources: The United States Department of Agriculture (USDA), National Institute of Food and Agriculture (NIFA), Northeastern Regional Aquaculture Center [USDA

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