Mass production of fertilized eggs by artificial insemination from captive-reared Pacific bluefin tuna (Thunnus orientalis)
Introduction
Owing to the high commercial value and increasing demand for bluefin tuna in the sashimi-sushi market, aquaculture industries have been developed for Atlantic bluefin tuna (Thunnus thynnus) in Mediterranean countries, southern bluefin tuna (Thunnus maccoyii) in Australia, and Pacific bluefin tuna (PBT) (Thunnus orientalis) in Mexico and Japan over the last decade (Miyake et al., 2010). However, these aquaculture industries are based on capture of wild tuna stocks, which can lead to depletion of those stocks. For a sustainable tuna farming industry, it is therefore necessary to establish a system in which the fish undergo their entire life cycle in captivity to reduce reliance on wild stocks.
Reproductive technologies under captive conditions are essential to develop viable full-life-cycle aquaculture. Fertilized eggs have been collected from captive-reared bluefin tuna species for larviculture to produce fingerlings. In Atlantic bluefin tuna, collection of the fertilized eggs from broodstock has been achieved at several farming sites in the Mediterranean Sea by spontaneous or hormone-induced spawning in rearing sea cages (Mylonas et al., 2010). Spawning of southern bluefin tuna has been reported under artificially controlled conditions in an onshore facility in Australia (Stehr, 2010). Reproduction of PBT in captivity has been studied in Japan over the last few decades. In 1979, Kinki University succeeded in achieving spontaneous spawning of sea cage-reared broodstock for the first time. Spontaneous PBT spawning has since been reported by several other research agencies and companies in Japan. These eggs have been used for research on larviculture technologies, and the full life-cycle was closed by Kinki University in 2002 (Masuma et al., 2008, Masuma et al., 2011, Sawada et al., 2005).
It is generally accepted that selective breeding for desirable traits is important for improving aquaculture productivity. An example of successful selective breeding is the increase in growth rate in red sea bream (Pagrus major), which is the major aquaculture species in Japan. The average body weight of 4-year-old broodstock increased 2.5 times and the average time to achieve the commercially desired size (1 kg) was shortened by 321 days by the selection for growth rate over six to seven generations (Murata et al., 1996). Similarly, genetic improvement by selection of commercially important traits has been reported in several other aquaculture species (Gjedrem and Baranski, 2009b). As with these other aquaculture species, a selective breeding program for bluefin tuna species is essential for further development of the bluefin farming industry.
Various technologies exist to determine genetically superior individuals in a fish population based on genetic and statistical applications. In addition, reproductive technologies help increase the efficiency of selective breeding. Artificial insemination (AI) is a fundamental technology for selective breeding because it allows design of various mating schemes (Nguyen et al., 2006). In bluefin tuna species, however, a technology for producing fertilized eggs by AI has yet to be established. One of the limiting factors for accomplishing AI in these species is that they are difficult to handle. Mature bluefin tuna are relatively large with very delicate skin, which can be easily damaged. Thus, handling the animals to collect sperm and ovulated eggs for AI can increase the risk of fatalities among the fish. Death of broodstock can lead to large economic losses, especially in the case of fish with high commercial value such as bluefin tuna. Because of this challenge, current artificial propagation of bluefin tuna species is totally dependent on one method that does not require touching the fish and involves collecting the fertilized eggs spawned in sea cages or onshore tanks (Partridge, 2013).
Handling fatalities are not usually a concern in standard aquaculture procedures because the fish are usually killed for use as a commercial product after being pulled from sea cages. For this reason, sea cage-harvested fish may be well suited for collection of gametes for AI. In the present study, therefore, we developed an AI method using gametes obtained from commercially harvested PBT to provide a new reproductive technology that could contribute to the development of effective breeding programs of bluefin tuna species.
Section snippets
Animals and rearing conditions
Commercially cultured PBT in standard procedures were used in this study. The fish were caught by purse seine in the western the Sea of Japan in June 2009. The mean fork length of the fish caught by this method was 55.1 ± 1.9 cm, and the mean estimated age calculated from the fork length, based on Itoh (2009), was 259.6 ± 32.4 days (0.7 ± 0.1 years) at the time of capture (± SD, n = 692). After a short rearing period (1–2 months) in adaptation sea cages set in the coastal area of the Tsushima Islands in
Results
We examined 2554 and 3817 harvested fish throughout the experimental periods in 2011 and 2012, respectively. The percentages of males and females, determined by random sampling, were 47.8 and 52.2%, respectively (n = 2454). Spermiation was observed in almost all of the harvested male fish (Fig. 2A, B), allowing sufficient semen to be collected in every trial. In addition, all of the sperm samples randomly selected from these fish showed high motility (n = 10 and 11 in 2011 and 2012, respectively),
Discussion
AI was successfully performed with PBT seven times in the present study. Consequently, sufficient fertilized eggs and hatched larvae were produced for large-scale larviculture in onshore tanks, and 1630–4410 fingerlings were successfully moved into offshore sea cages in each rearing trial. These results demonstrate that the fertilized eggs from this method are practicable for production of fingerlings to supply bluefin tuna aquaculture efforts.
There has been little study of the application of
Acknowledgments
The authors are grateful to the staff of Seinan Suisan Co. Ltd. for their assistance with maintenance and sampling of the fish. We also wish to thank the staff of Oita Marine Biological Technology Center for their useful advice and helpful discussion.
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Cited by (9)
Normal hatching rate estimation for bulk samples of Pacific bluefin tuna (Thunnus orientalis) eggs using deep learning
2022, Aquacultural EngineeringCitation Excerpt :For this reason, normally hatching success is widely accepted as the ultimate measures of egg quality in aquaculture species (Brooks et al., 1997). In fact, some determination methods of normally hatching success are used for routine application in aquaculture hatcheries of many fish species (Endo et al., 2016; Kjørsvik et al., 2003; Jerez et al., 2012), allowing fish farmers allocation/discarding eggs or hatched larvae for/from further culture procedures. However, as PBT aquaculture hatcheries are often located far from spawning facilities, which are located in regions with suitable conditions for breeding, the fertilized eggs should be transported immediately to the hatcheries during embryogenesis when the eggs have high tolerance to physical stress (Chattopadhyay et al., 2021; Kurata et al., 2017).
Optimization of cold-shock conditions for the induction of triploidy in the Pacific bluefin tuna, Thunnus orientalis (Temminck et Schlegel)
2021, AquacultureCitation Excerpt :In general, fertilized eggs obtained by artificial insemination have been used for the induction of triploidy in previous studies as it is essential to perform the triploidy induction treatment at a precise time after fertilization (Felip et al., 2001). In tuna species, however, there are high risks of losing valuable broodstock during the process of artificial insemination, since these species generally show low tolerance to handling stress (Endo et al., 2016; Yazawa et al., 2019). Recently, we have demonstrated that T. orientalis can be induced to spawn with daily frequency by manipulating environmental cues in land-based tanks (Higuchi et al., 2015, 2019).
In vitro digestion comparison from fish and poultry by-product meals from simulated digestive process at different times of the Pacific Bluefin tuna, Thunnus orientalis
2016, AquacultureCitation Excerpt :However, to the authors' knowledge, the simulation of gastric and pancreatic proteolysis of FM and PBM at different time points has not been evaluated. In addition, because of the high commercial value and increasing demand for the Pacific Bluefin Tuna (Thunnus orientalis; Endo et al., 2016), the development of a formulated feed which could improve the high feed conversion ratio of the present culture practice using raw sardine (Zertuche-González et al., 2008; FAO, 2014) will be important. Thus, a well-balanced easily digestible formulated feed is necessary for this and other carnivorous species.
Aquaculture: A rapidly growing and significant source of sustainable food? Status, transitions and potential
2016, Proceedings of the Nutrition Society
- 1
Present address: Seinan Suisan Co. Ltd., 3620–8 Niinameura, Kamiura, Saiki, Oita 879–2603, Japan.
- 2
Present address: Kurose Suisan Co. Ltd., 2-15-4 Nishihama, Kushima, Miyazaki 888-0012, Japan.