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03 de abril de 2013
This laboratory located in Central America has the only place in the world where tuna eggs, larvae and juveniles can be obtained almost year round. Many investigations there have obtained valuable information about this fish behavior and its potential as an aquaculture species.
By Maria S. Stein, Daniel Margulies, Vernon P. Scholey and Jeanne B. Wexler
The Inter-American Tropical Tuna Commission (IATTC) is taskedwith the management and conservation of tuna and billfish inthe Eastern Pacific Ocean. Yellowfin tuna, Thunnus albacares, is one of themost commercially important species within the IATTC’s study area.
This is a pelagic, or open-ocean,species, making it difficult to study inits natural habitat. In order to address the lack of biological information about adult and early-life stages of tuna, crucial for species management, the IATT Cestablished the Achotines Laboratory,where these aspects of its biology could be studied in a controlled, experimental environment. This unique facility, located in the Republic of Panama, currently maintains a broodstock of yellowfin tuna in an in-ground, concrete tank. Members of the IATTC’s Early Life-History (ELH) Group and collaborating scientists have nearly year-round access to study captive tuna at various stages of life.
Establishment and Development of the Laboratory
The Achotines Laboratory is situated on the southern tip of the Azuero Peninsulaon the Pacific coast of the Republic of Panama, adjacent to Achotines Bay.Its carefully-selected location provides many advantages for scientists studying tropical tunas. It is located in an area of the coastline where the continental shelf is narrow; water is over 200m deep just 6-10 km from the shore line,which provides relatively quick access to oceanic waters where yellowfin tuna,among other animals and samples, can be collected and transported back tothe Laboratory. The sea-surface temperature in this region typically ranges from 21-29˚C year-round, which eliminates the necessity of manipulating the water temperature in order to maintain the spawning population of yellowfin tuna.
After the Laboratory’s inauguration in 1985, research initially focused on coastal tropical tunas and mackerel,such as black skip jack (Euthynnuslineatus), bullet and/or frigate tuna (Auxis spp.), and sierra mackerel(Scomberomorus sierra). Many studies of early life history and reproductive biology were conducted during this time.For the first time, the life cycle of black skipjack was completed in captivity by rearing field-caught larvae to maturity.ELH scientists also successfully developed a captive spawning population of black skipjack, another world-first.
In 1993, the IATTC, the Overseas Fishery Cooperation Foundation (OFCF) of Japan, and the government of the Republic of Panama initiated a joint project with the objective of investigating the culture and spawning incaptivity of yellowfin tuna, snappers(Lutjanidae ssp.), and drums (Sciaenidaessp.) in land-based tanks to provide eggs, larvae and juveniles for research purposes. The undertaking required a massive infrastructure expansion of the laboratory facilities in order to hold and maintain yellowfin tuna and providec ultured prey for their larvae. A circular,in-ground concrete tank, measuring 17m in diameter and 6 m in depth witha 1,300 m3 capacity, was built forthe main yellowfin broodstock. Wild tuna were caught in nearby waters and brought back to the laboratory in live wells aboard skiffs. The yellowfin broodstock was successfully establishedin 1996 and natural spawning occurred in the fall of that year and has continued on a near-daily basis to this day.
Five smaller in-ground concrete tanks were also added during this initial expansion, along with facilities forin cubating eggs, rearing larvae and juveniles, and producing algae and rotifers for feeding the fish. Development of the Laboratory has continued overthe years and today Achotines boasts an analytical laboratory, a nutritional analysis laboratory, a DNA laboratory,a library and a conference room. There is also office space and housing for scientists, a workshop, and a pier in Achotines Bay for vessel operations.
Research on yellowfin tuna
A wealth of information has resulted from work with both the adult and the egg, larval and juvenile stages of yellowfin tuna at the Achotines Laboratory.The ELH researchers and collaborating scientists have studied aspects of tuna biology that have an impact on both management and culture of the species.
Yellowfin Tuna Broodstock
The broodstock yellowfin are fed a diet of squid, herring andanchovy, supplemented with vitamins and minerals. Dailyfood rations are regulated by the feeding activity of the fish. Abio energetics model has also been used to assure the rationis sufficient to fulfill energy demands. A diet of half squid/halffish has been found to provide adequate nutrition for almostcontinuous spawning, while avoiding excessive fat accumu-lation.
There have been estimated growth rates in length andweight of captive fish and it has been found that both growthrates decreased with increasing size of fish. Average growthin length of broodstock fish ranged from 11-62 cm per yearand average growth in weight from 7-33 kg per year. Of the initial wild yellowfin caught offshore as broodstock candidates in 1996, around half survived capture and trans-port, while about a third made it through a quarantine periodin a smaller tank before joining the main broodstock. Smallerfish survive capture and handling better than larger fish.
Theaverage residency time in the main tank is two years, withthe maximum time being six years. Most of the deaths in thetank are due to wall strikes, in which a fish collides with theside of the tank, dying instantly or shortly there after due tospinal injury or secondary infection from sustained injuries. Incidence of wall strikes has been more frequent when the fish density in the tank has increased to a maximum of 0.65kg/m3, so a lower target density is maintained.
The growthrate of the captive yellowfin is lower overall than the estimated growth rates of wild yellowfin in the eastern Pacific, likely due to confinement in the tank.The yellowfin broodstock began spawning in the maintank in October, 1996 and spawning has continued almostdaily. During the process, which has been filmed by ELHscientists, the fish exhibit courtship behavior for 1-4 hoursprior to spawning. Most of the fish in the tank form a loosegroup near the bottom of the tank. A smaller group of about2-5 fish separate away from the main group and one ofthem, presumably female, is chased by one or more others, presumably male. Spawning occurs when the female fishreleases eggs into the water and the males swimming behindher release milt; the eggs are fertilized when they mix withthe milt in the water column. This type of fertilization, called broadcast spawning, is common among tuna species, but because it occurs naturally in the open ocean, and usually at night, these courtship and spawning behaviors have beenvery rarely observed in the ocean. Working with the adult fish has led to valuable insight and multiple publications on topics such as broodstock establishment, health and growth, physiology, genetics, and courtship and spawning dynamics of the adult fish.
Early Life Stages of Yellowfin
Eggs from adult fish are collected from the main tank andare routinely used in experiments on the egg, larval andjuvenile life stages in smaller tanks. ELH Group members conduct experiments designed to gain insight into the biological and physical factors that influence survival during the stages before the fish are large enough to enter the fishery(also known as prerecruit stages). This is an important time in the life cycle due to the high growth and mortality rates experienced. Small changes in vital rates (survival, growth) during this period have the potentialto have tremendous effects on thenumber of resulting adult fish. Studieshave covered a range of topics, inclu-ding investigations of the effects ofwater temperature, dissolved oxygen,micro-turbulence, light, and feeding ongrowth and survival of yellowfin larvae.Recently, the effects of ocean acidification are receiving increased attention worldwide. For tuna, early lifestages are sensitive to environmental changes but potential impacts of ocean acidification on tuna populations are unknown. Research trials were completed at the Achotines Laboratory in late 2011 examining the potential effects of ocean acidification on the survival and growth of yellowfin eggs and larvae. These trials were conducted in collaboration with scientists from the Secretariat of the Pacific Community (SPC), and were funded by the Pelagic Fisheries Research Program (PFRP) of the University of Hawaii.
Collaborations
Much of the information that is gained from the experiments and rearing of tuna can be applied to tuna ecology and aquaculture, as similar biological information about tuna is required in both fields, but for different applications. This has led to multiple collaborations for the IATTC’s ELH Group.
Comparative studies ofyellowfin and Pacific bluefinearly life history: SATREPS
In April 2011, the IATTC, Kinki University of Japan, and the Autoridad de Recursos Acuáticos de Panama (ARAP) began a comparative study of the early life history and reproductive biology of yellowfin tuna and Pacific bluefin tuna(Thunnus orientalis). This joint researchproject is being conducted by faculty and staff of Kinki University, the
ELH Group of the IATTC, and scientists of ARAP, mostly at the Fisheries Laboratory of Kinki University and the Achotines Laboratory, and will continue through March 2016. The study will be the first in the world to investigate important comparative aspects of the reproductive biology, genetics, and early life history of these two species of tunas. The project will also support graduate research through Kinki University for selected members of all three participating groups. It is being implemented under the Science and Technology Research Partnership for Sustainable Development (SATREPS); the studies conducted in Japan are supported by the Japan Science and Technology Agency (JST), and those in Panama by the Japan International Cooperation Agency (JICA).
Joint studies with HubbsSea World Research Institute(HSWRI)
In 2010 and 2011, eggs and/or larvae of yellowfin tuna were successfully shipped by air from the Achotines Laboratory to the Hubbs Sea World Research Institute (HSWRI) in San Diego, California, USA, as partof a feasibility study funded by the Saltonstall-Kennedy Program, U.S.National Oceanic and Atmospheric Administration (NOAA). The study proved that it is possible to send these kinds of samples from Panama to the United States for research purposes,and the success of the project was instrumental in the IATTC and HSWRI recently being awarded a California Sea Grant project designed to continue and expand the air shipment trials. Thenew project began in May 2012, and will continue for 3 years.
IATTC-University of Miami annual workshop
Since 2003, the IATTC and theUniversity of Miami’s AquacultureProgram have jointly hosted anannual workshop entitled “Physiology and Aquaculture of Pelagics with Emphasis on Reproduction and Early Developmental Stages of YellowfinTuna” at the Achotines Laboratory.International researchers, industry professionals and University of Miami graduate students gather to studyand share advanced technologies and improved methods for experimentalstudies and rearing of larval tunas and other species of marine fish. A fee forthe participants and students covers the expenses of conducting the wor-kshop.
Learn More about Achotines Laboratory
The IATTC’s Achotines Laboratory isan internationally recognized research facility dedicated to the study of tunaand tuna-like species. Being the only facility in the world with nearly year-round availability of tuna eggs and larvae for research purposes, it is valued both among the scientific and aquaculture communities world-wide.
