Introduction
Tilapia (Oreochromis spp.) culture has been the principal aquacultural activity in southeastern Mexico since the 1960s and 1970s (Fitzsimmons, 2000). With the introduction of tilapia into Mexico, the different institutions responsible for fish production created very high expectations among Mexican farmers and investors. Unfortunately, these expectations were never fulfilled for a variety of reasons. Loss of the introduced lineages, lack of effective genetic selection programs, and poor management decisions have created disappointment and uncertainty regarding tilapia culture in Mexico.
Meanwhile, other countries in Central and South America have demonstrated that tilapia culture can be a valuable investment for both business and social projects.
Because of its geographic and hydrological components, the southeastern region of Mexico has been considered as one of the best areas in Mexico for aquaculture, especially for tilapia culture. Currently there are six main tilapia hatcheries in the Mexican states of Tabasco and Chiapas that provide fry to more than 5,000 small-scale tilapia farmers. However, the quality and quantity of the fry provided have been constantly criticized by the farmers to the hatchery managers. In 1992, Contreras-S‡nchez et al. (1992) documented in an internal report for the StateÕs Office for Development (Secretar’a del Desarrollo) the need for establishing a new tilapia line appropriate for meeting the needs and conditions of the Central American tropics. This document also suggested the need to establish
broodstock selection programs and to form high-quality broodstock lots in the fry production facilities. To date, all hatcheries in Tabasco and Chiapas are buying fry from the Mexican states of Veracruz, Oaxaca, and Guerrero to partially fulfill the demand. However, the quality of the fry is still low.
Methods and Materials
This study was conducted at the state tilapia hatchery Jose Narciso Roviriosa, located in Teapa, Tabasco, as a collaborative effort between Universidad Ju‡rez Aut—noma de Tabasco (UJAT) and the office for Agriculture and Fisheries Development (SEDAFOP) of Tabasco. Three lines of tilapia were evaluated: 1) the line that the hatchery has traditionally used, 2) a wild line from the Usumacinta River basin, and 3) a line obtained from Egypt by the State government.
Egypt Line
A selective breeding program was initiated in 2001 using 220 females and 110 males selected from the batch of fish purchased from Egypt by the State government. This first batch was selected using a discriminant analysis for fish that best resembled Nile tilapia. The analysis was based on length, weight, number of scales, fins, head length, mouth diameter, and eye diameter. These fish were stocked in 200 m2 ponds for grow-out. From the fry obtained, three selections were made: one at 60 days, a second at 120 days (at this point the fish were separated by sex), and a third at 11 months. Six hundred females and 400 males were selected based on a combination of best length and condition factor to obtain an F1 generation. These fish were stocked in 200 m2 ponds and allowed to breed. From the fry obtained, 60% of the total were selected for grow-out. After four months, another selection of the stocked fish was conducted. Two hundred females and 66 males were selected based on the best weight and condition factor and used as breeders for the proposed study.
Wild Adult Tilapia
We sampled tilapia from four areas in the State of Tabasco: Balanc‡n, Jonuta, Teapa, and Huimanguillo (Figure 1). All areas were sampled using gill nets. All the fish captured were separated by sex, transferred to concrete ponds at the laboratory of aquaculture at UJAT, and fed three times a day. After conditioning, fish were selected and bred. Due to high mortality in most samplings, only 26 males and 23 females from the San Pedro River (SPR), Balancan were bred.
State Tilapia Hatchery, Jose Narciso Rovirosa (JNRH)
Adults commonly used at the farm for reproduction were separated by sex and used as our reference line.
Females used as broodstock (n = 5) were measured to de
Figure 1. Sites selected for sampling wild tilapia. 1) Balanc‡n, 2) Jonuta, 3) Teapa, and 4) Huimanguillo.
