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PD/A CRSP Aquanews-Summer 2002

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The Oregon–Mexico Connection

by Carl B. Schreck and Guillermo R. Giannico, Oregon State University, and Wilfrido Contreras-Sánchez, Gabriel Márquez-Couturier and Mario Fernández Pérez, Universidad Juárez Autónoma de Tabasco, Mexico

his OSU/UJAT collaborative project addresses some of the major problems that small farmers face in Southeastern Mexico. Three areas are critical for restructuring and supporting sustainable aquaculture in Mexico and Central America: 1) implementing masculinizing systems for tilapia and native fish species that are safe for the fish culturist and the environment; 2) producing a new line of tilapia for broodstock replacement; and 3) diversifying aquacultural practices using native species. We have brought together a very strong group of twenty students, sixteen of whom are supported by the PD/A CRSP—12 undergraduate and 4 graduate students—all of them working in the UJAT laboratory on their own theses projects.

Yara Rivera Márquez and Alejandro Mcdonal Vera stock hapas with tilapia fry for masculinization treatment.
We have implemented an intensive masculinizing system equipped with an activated-charcoal filter and tested different amounts of charcoal (0, 2.5, and 5.0 k) to capture excess methyltestosterone (MT) present in the water. A preliminary trial run with an initial number of 7,000 fry yielded more than 3,000 masculinized fry (of which more than 99 % were males) in all units. In a second trial that started with approximately 21,000 fry, we obtained more than 9,000 fry in the units containing 2.5 and 5.0 k of charcoal, while only about 4,000 were present in the unit containing no charcoal.

The fish are in a growout pond and the efficacy of MT feeding will be assessed shortly for this trial. We have been monitoring nitrates, nitrites, and ammonia concentrations in water; high concentrations may be responsible for high mortalities in the preliminary trial. Water and charcoal samples have been collected and kept frozen to be analyzed at Oregon State University for MT concentrations. We are currently running another trial using 18,000 fry in each experimental unit.

Aquaculture Facilities at UJAT

The laboratory comprises an area of 1972 m2. Site facilities include 2 wet rooms, 2 offices, a chemistry lab, a sampling room, an ecophysiology lab, a constant temperature room, a small library and a kitchen. There are 3 concrete ponds with an area of 50 m2 each and one earthen pond with an area of 200 m2 that are used for reproduction and grow-out. One circular tank (240 m3) is used for tilapia juvenile grow-out. Three 8 m3 tanks are used for studies on masculinization of tilapia fry, 5 circular 6 m3-tanks are used for native cichlids reproduction, and two 16 m3-tanks are used for tilapia broodstock selection. Many experiments are run in recirculating systems. The facility has 6 systems composed of twelve 20-l buckets each and one with 27 buckets. Studies on fry growth and sex differentiation are conducted in a system with 9 tanks with 1,000 l capacity each. Two outdoor recirculating systems have a total of 72 tanks with a capacity for 120 l.

In another set of
Rocío Chan Rodríguez and Maria de Jesús Contreras García work on a recirculating system used for growing out tropical gar juveniles. This experiment was performed to determine sex inversion can be performed on gars because females grow larger than males.
experiments we are evaluating the administration of bioencapsulated trenbolone acetate (TA) for masculinization of tropical gar and mojarra castarrica fry and estradiol (E2) for feminization of tropical gar fry, using Artemia nauplii as a vehicle. We have validated the incorporation of both steroids in the A. nauplii. After two hours of treatment, we detected more than 6,000 picograms (pg) of E2 and more than 6,500 pg of TA per gram of A. nauplii. Concentrations of both steroids remained elevated after 24 hours. Fish were fed with enriched A. nauplii and are currently in growout recirculating systems, until they reach sampling size.

At the Mariano Matamoros tilapia farm we are finishing the selection of the first line of Nile tilapia juveniles that will be tested as broodstock. This selection has been conducted using weight and standard length as the main response variables.

The establishment of good quality broodstock treatments, their distribution to local hatcheries, and the implementation of intensive masculinization programs are basic steps for sustainable aquaculture. These actions can improve significantly the production of good quality fingerlings and have a favorable impact on more than 5,000 subsistence farmers and medium-scale producers.

Tabasco is considered among the States of Mexico with the highest potential for both intensive and extensive aquacultural development. Moreover, fish consumption constitutes an important part of the rural lifestyle in the State of Tabasco. Therefore, research efforts underway are logical initial steps toward developing sustainable aquaculture in the region.

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