Advances in tuna aquaculture
Chapter 7: Reproduction, broodstock management and spawning in captive Atlantic bluefin tuna. Elsevier (2015)
Understanding the reproductive biology of Atlantic bluefin tuna (ABFT) is important to both managing its fishery and developing hatchery technologies to close its life cycle in aquaculture. Globally, ABFT is comprised of two populations, the eastern and western stocks, with known breeding areas in the Mediterranean Sea and the Gulf of Mexico, respectively. Gametogenesis takes place during spring and early summer, and spawning usually occurs from May to July, coinciding with the rise of water temperature. Females display an asynchronous ovarian development, typical of a batch spawner. Comparing the endocrine-reproductive cycle in wild and captive ABFT led to the development of a hormone-based therapy to induce spawning in captive broodstock. While captivity affects gametogenesis in ABFT, at least some of the captive fish spawn spontaneously, which can be enhanced and prolonged using hormonal induction. Massive spawning of captive ABFT enabled the first aquaculture production of marketable fish, demonstrating the biological feasibility of this industry. Current research on hormonal regulation of its puberty may lead to the use of smaller ABFT broodstock, simplifying their husbandry and management. This, together with the establishment of land-based broodstock operations, will enable efficient and cost effective on-demand and year-round production of ABFT seeds to drive the consistent farming of this fish
Sparidae: biology and aquaculture of gilthead sea bream and other species, PAVLIDES, M. AND MYLONAS, C.C. (EDITORS), Wiley-Blackwell (2011)
The family of Sparidae --sea breams and porgies-- is a moderately sized, but morphologically and ecologically highly diverse family of percoid fishes. Sparids are widely distributed, highly appreciated and of commercial significance for both fisheries and aquaculture in many areas around the world. The history of red sea bream (Pagrus major) aquaculture in Japan is the oldest among marine fishes, while the domestication of gilthead sea bream (Sparus aurata) that started in Europe in the 70's resulted in the development of a large scale industry in the Mediterranean Region, and beyond. Fueled by the interest in their cultivation, sparid fishes have been used as models in studying various aspects of fish biology. For example, a large body of basic research produced significant knowledge in the area of reproduction, especially in the area of hermaphroditism that is a major characteristic of the Sparidae family. This book aims to gather, for the first time, the published information in one volume, by presenting the current knowledge in the evolution, biology, physiology and culture of sparid fishes, drawing heavily in some parts from the extensive research undertaken with the gilthead seabream. The book covers both generic aspects and main production obstacles in the currently cultured species, and it is organized with a balance in mind between basic and applied aspects of Sparidae biology and farming. It is targeted towards fish biologists and aquaculture professionals, as well as stakeholders involved in fisheries management and aquaculture. It will also be a useful reference for students enrolling in the field of aquaculture and management of marine recourses.
Sparidae: Biology and Aquaculture (Wiley-blackwell, 2011)
Chapter 4: Reproduction and broodstock management
The Sparidae is a cosmopolitan family, and sparid fishes can be found and reproduce in both temperate and tropical seas around the world. Most of the members of this family are sequential hermaphrodites --either protogynous, such as the red porgy (Pagrus pagrus) or protandrous, such as the gilthead seabream (Sparus aurata)--, but gonochoristic species also exists, such as the common dentex (Dentex dentex). Fish in this family have a long spawning season ranging between 60 and 150 days, and spawn daily or in a highly cyclical fashion. Fecundity is very high ranging between 0.4 and 3.2 million eggs per Kg of female body weight. The eggs are pelagic, transparent and have a diameter between 800 and 1000 µm. Hormonal therapies have been developed to address the reproductive dysfunctions that exist in the early days of establishing captive wild or hatchery-produced broodstocks. At present, most Sparidae that are cultured commercially reproduce spontaneously in captivity and hatchery produced broodstocks have been developed and in some cases selected for traits of commercial importance.
Atlantic bluefin tuna (Thunnus thynnus) farming and fattening in the Mediterranean Sea. Reviews in Fisheries Sciences (2010)
The Atlantic bluefin tuna (Thunnus thynnus) is one of the tunas with the highest commercial value and is supporting the capture-based tuna aquaculture industry in the Mediterranean Sea. This is a seasonal activity and it involves the capture of fish from the wild and their rearing in sea cages for periods ranging between 3 months to 2 years. Short-term rearing is done mainly to (a) achieve a greater body fat percentage and (b) obtain a better price by not flooding the market in the brief fishing period. Due to the increasing fear for a collapse of the fishery, the International Commission for the Conservation of Atlantic Tunas (ICCAT) currently reduced the TACs for 2010 to 13,500 mtn from 32,000 mtn previously. Therefore, there is great interest to establish a proper and sustainable tuna aquaculture industry. This necessitates the development of specific technologies for tuna aquaculture that will not rely on captured individuals from the wild, as it is practiced today. This paper reviews the methods used for the farming and fattening of the species in the Mediterranean Sea, and the current status of the efforts at controlling reproduction in captivity.
Broodstock management and hormonal manipulations of reproduction. General and Comparative Endocrinology (2010)
Control of reproductive function in captivity is essential for the sustainability of commercial aquaculture production, and in many fishes it can be achieved by manipulating photoperiod, water temperature or spawning substrate. The fish reproductive cycle is separated in the growth (gametogenesis) and maturation phases (oocyte maturation and spermiation), both controlled by the reproductive hormones of the brain, pituitary and gonad. Although the growth phase of reproductive development is concluded in captivity, oocyte maturation (OM) and ovulation in females, and spermiation in males may require exogenous hormonal therapies. In some fishes, these hormonal manipulations are used only as a management tool to enhance the efficiency of egg production and facilitate hatchery operations, but in others exogenous hormones are the only way to produce fertilized eggs reliably. Hormonal manipulations of reproductive function in cultured fishes have focused on the use of either exogenous luteinizing hormone (LH) preparations that act directly at the level of the gonad, or synthetic agonists of gonadotropin releasing hormone (GnRHa) that act at the level of the pituitary to induce release of the endogenous LH stores, which, in turn act at the level of the gonad to induce steroidogenesis and the process of OM and spermiation. After hormonal induction of maturation, broodstock should spawn spontaneously in their rearing enclosures, however, the natural breeding behaviour followed by spontaneous spawning may be lost in aquaculture conditions. Therefore, for many species it is also necessary to employ artificial gamete collection and fertilization. Finallly, a common question in regards to hormonal therapies is their effect on gamete quality, compared to naturally maturing or spawning broodfish. The main factors that may have significant consequences on gamete quality --mainly on eggs-- and should be considered when choosing a spawning induction procedure include (a) the developmental stage of the gonads at the time the hormonal therapy is applied, (b) the type of hormonal therapy, (c) the possible stress induced by the manipulation necessary for the hormone administration, and (d) in the case of artificial insemination, the latency period between hormonal stimulation and stripping for in vitro fertilization.
New technologies in aquaculture (Taylor & francis, 2009)
Chapter 4: COntrolling fish reproduction in aquaculture
Methods in reproductive aquaculture (Taylor and Francis, CRC, 2008)
Chapter 1: Reproduction and control of spermiation, ovulation and spawning in cultured fish
The fish oocyte (Springer, 2007)
Chapter 15: Promoting oocyte maturation, ovulation and spawning in farmed fish
Aquaculture, especially of marine species, is quite a new agricultural activity in relation to domestic animal production. With the exception of carp culture (family Cyprinidae) in Asia which started many centuries ago, and rainbow trout (Oncorhynchus mykiss) farming in Europe and North America which was commercialized in the last century, aquaculture as we know it is being practiced for only a few decades. As a result, it is doubtful that a «domestic» fish species exists today, at least according to the interpretation of the word in terrestrial animal husbandry. In addition, even carp and rainbow trout, which are considered highly domesticated, do not reproduce readily in captivity.
In order to establish aquaculture as a successful and efficient agricultural activity, there is a need to control reproductive processes in fish, in order to obtain high quality seed (i.e., eggs and sperm) and produce juveniles for grow-out without the need to obtain them from the wild. Surprising as it may appear, the aquaculture industry of species such as the freshwater eels (Anguilla spp.), the yellowtail and greater amberjack (Seriola spp.), groupers (Epinephelus spp.) and the bluefin tuna (Thunnus thynnus), is based almost exclusively on the collection of juveniles or adults from the wild. In some fish species, it is sometimes possible to control reproduction by manipulating environmental parameters, such as photoperiod, water temperature, tank depth and/or volume, spawning substrate, etc. Even then, the existence of the artificial environment with the associated human presence is by default an inhibiting factor on reproduction, whereas it is often impractical or even impossible in some fishes to simulate the environmental parameters accompanying reproductive maturation in the wild (i.e. spawning migration, depth, riverine hydraulics, etc.). Therefore, hormonal therapies have been employed in the past decades in order to control reproduction in cultured fishes and induce or synchronize oocyte maturation (OM), ovulation and spawning. In some species, hormonal manipulations are the only way to produce fertilized eggs, whereas in other fishes exogenous hormones are used only as a management tool to enhance the efficiency of egg production and facilitate hatchery operations.
For example, in salmonids, which require insemination in vitro for the production of fertilized eggs, OM and ovulation are often induced with hormones. This is to synchronize egg collection and fry production, thereby minimizing handling and stress to the fish, and reducing labor requirements. In Pacific salmon (Oncorhynchus spp.), hormonal therapies can also advance ovulation by a few weeks, thus reducing losses due to pre-spawning mortality. Hormonal therapies in fishes are also employed for the collection of gametes for inter-specific hybridization and chromosome set manipulation. Finally, genetic selection also requires hormonal therapies to enable proper maturation and timely collection of gametes for artificial fertilization. Therefore, hormonal therapies have an important role in broodstock management, and will continue to be a necessary tool even after fish become properly «domesticated» and reproduce spontaneously in captivity.
In order to establish aquaculture as a successful and efficient agricultural activity, there is a need to control reproductive processes in fish, in order to obtain high quality seed (i.e., eggs and sperm) and produce juveniles for grow-out without the need to obtain them from the wild. Surprising as it may appear, the aquaculture industry of species such as the freshwater eels (Anguilla spp.), the yellowtail and greater amberjack (Seriola spp.), groupers (Epinephelus spp.) and the bluefin tuna (Thunnus thynnus), is based almost exclusively on the collection of juveniles or adults from the wild. In some fish species, it is sometimes possible to control reproduction by manipulating environmental parameters, such as photoperiod, water temperature, tank depth and/or volume, spawning substrate, etc. Even then, the existence of the artificial environment with the associated human presence is by default an inhibiting factor on reproduction, whereas it is often impractical or even impossible in some fishes to simulate the environmental parameters accompanying reproductive maturation in the wild (i.e. spawning migration, depth, riverine hydraulics, etc.). Therefore, hormonal therapies have been employed in the past decades in order to control reproduction in cultured fishes and induce or synchronize oocyte maturation (OM), ovulation and spawning. In some species, hormonal manipulations are the only way to produce fertilized eggs, whereas in other fishes exogenous hormones are used only as a management tool to enhance the efficiency of egg production and facilitate hatchery operations.
For example, in salmonids, which require insemination in vitro for the production of fertilized eggs, OM and ovulation are often induced with hormones. This is to synchronize egg collection and fry production, thereby minimizing handling and stress to the fish, and reducing labor requirements. In Pacific salmon (Oncorhynchus spp.), hormonal therapies can also advance ovulation by a few weeks, thus reducing losses due to pre-spawning mortality. Hormonal therapies in fishes are also employed for the collection of gametes for inter-specific hybridization and chromosome set manipulation. Finally, genetic selection also requires hormonal therapies to enable proper maturation and timely collection of gametes for artificial fertilization. Therefore, hormonal therapies have an important role in broodstock management, and will continue to be a necessary tool even after fish become properly «domesticated» and reproduce spontaneously in captivity.
Use of GnRHa-delivery systems for the control of reproduction in fish. Reviews in Fish Biology and Fisheries (2001)
The most commonly observed reproductive dysfunctions in cultured fishes are the unpredictability of final oocyte maturation (FOM) in females, and the diminished volume and quality of sperm in males. Gonadotropin-releasing hormone agonists (GnRHa) have been used extensively in order to stimulate the release of pituitary luteinizing hormone (LH) required to induce FOM, ovulation and spermiation. Because multiple hormonal treatments are often necessary for a successful response, fish must be monitored and handled extensively, which is labor intensive, stressful to the fish and can often result in broodstock mortalities. To ameliorate this problem, sustained-release delivery-systems for GnRHa have been developed during the last two decades and have been increasingly applied in controlling reproduction of a variety of cultured fishes. Solid implants of cholesterol or poly[ethylene-vinyl acetate], and biodegradable microspheres of poly[lactide-glycolide] or poly[fatty acid dimer-sebasic acid] release GnRHa for periods of a few days to many weeks. GnRHa-delivery systems do not cause desensitization of the pituitary gonadotrophs in fish, and by stimulating a sustained elevation of plasma LH they induce the natural progression of plasma steroid increases associated with FOM and spermiation. This method has been used with very encouraging results in females of more than 40 cultured species and has been effective in inducing FOM, ovulation or spawning in fish with synchronous, group-synchronous and asynchronous ovarian development. In males, GnRHa-delivery systems have been tested in more than 20 species, producing significant increases in milt production for up to 5 weeks. Future research should focus on the optimization of this technology in terms of (a) using the most potent GnRHa, (b) identifying the most appropriate GnRHa release kinetics according to the reproductive biology of different species, and (c) determining minimum effective doses. Developments in these areas will greatly enhance the effectiveness and efficiency of GnRHa-delivery systems, while at the same time reduce their cost and make them more affordable to the aquaculture industry.
REPRODUCTIVE BIOTECHNOLOGY IN FINFISH AQUACULTURE (ELSEVIER, 2001)
CHAPTER 6: ENDOCRINE MANIPULATIONS OF SPAWNING IN CULTURED FISH: FROM HORMONES TO GENES
Almost all fish reared in captivity exhibit some form of reproductive dysfunction. In females, there is often failure to undergo final oocyte maturation, ovulation and spawning; while in males milt production may be reduced and of low quality. These dysfunctions are due to the fact that fish in captivity do not experience the conditions of the spawning grounds, and as a result there is a failure of the pituitary to release the maturational gonadotropin, luteinizing hormone (LH). Reproductive hormones have been utilized since the 1930s to stimulate reproductive processes and induce ovulation/spermiation and spawning. The first methods employed freshly-ground pituitaries collected from reproductively mature fish, which contained gonadotropins (mainly LH) and induced steroidogenesis and gonadal maturation. Eventually, purified gonadotropins became available, both of piscine and mammalian origin -- e.g., carp or salmon gonadotropin, and human chorionic gonadotropin. In the 1970s, spawning induction methods begun employing the newly discovered gonadotropin-releasing hormone (GnRH), which induces the secretion of the fish’s own gonadotropin from the pituitary, thereby overcoming the endocrine failure observed in captive broodstocks. Development of highly potent, synthetic agonists of GnRH (GnRHa) constituted the next generation of hormonal manipulation therapies, and created a surge in the use of hormones to control reproductive processes in aquaculture. The most recent development is the incorporation of GnRHa into polymeric sustained-release delivery systems, which release the hormone over a period of days to weeks. These delivery systems alleviate the need for multiple treatments and induce (a) long-term elevation in sperm production and (b) multiple spawning in fish with asynchronous or multiple-batch group-synchronous ovarian physiology. Based on the recent discovery of GnRH multiplicity in fish and the increasing understanding of its functional significance, new GnRH agonists can be designed for more potent, affordable and physiologically-compatible spawning induction therapies. Future strategies for improved spawning manipulations will be based on understanding the captivity-induced alterations in the GnRH system, and on new approaches for their repair at the level of GnRH gene expression and release.