Aquaculture CRSP 21st Annual Technical Report
Survey of Tilapia-Shrimp Polyculture in Mexico and Honduras
Tenth Work Plan, New Aquaculture Systems/New Species Research 3C (10NSR3C)/Experiment/Mexico
University of Arizona, USA
Wilfrido M. Contreras-Sánchez, Alejandro Macdonald-Vera and Ulises Hernández-Vidal
Laboratorio de Acuacultura
División Académica de Ciencias Biológicas, UJAT
The majority of the Mexican shrimp farming industry is situated in the Northwest of Mexico. However, shrimp aquaculture in Mexico is in crisis due to a mix of the depressed world shrimp market and disease outbreaks causing decreased yields (Panorama Acuícola, 2002).
To determine the potential for shrimp-tilapia polyculture in the area, we conducted surveys in the State of Sinaloa -the most important shrimp aquaculture area in Mexico. We visited 63 farms, which represent 63.5 % of the total number of farms in the Northwest. Four of those farms were closed for inactivity (6.35%) and ten did not respond to the survey (15.3%). We visited 22 farms in the municipality of Guasave (45% of the total surveyed). Guasave is the most important area in the State for shrimp culture.
The data collected showed that farm size varies considerably (from 9 to 1,000 hectares). The production varies from 1 to 2,300 ton/year. Most farms (52%) produce shrimp in two cycles per year (January-June and July-December). Twenty-three farms (46%) reported a single cycle per year (January-June) and one farmer claims to be able to produce shrimp in three cycles a year (2%).
All farmers use PL12 postlarvae to stock their ponds. The cost of 1,000 postlarvae in Sinaloa ranges between 5.5 to 6.5 USD. Most farms (67%) report culture cycles of 120 days and 33% of the farms report cycles of 150 days. The density used to stock ponds varies from 5 to 40 shrimp/m2, but most farms stock between 10 and 20 shrimp/ m2 (56.9%). The average weight of shrimp harvested in the farms surveyed is 18.0 g ranging from 7 to 35 g; however, the most common weight of shrimps falls between 15 to 25 g (58.4%). The size of the shrimp harvested is directly related to the density used to stock the ponds.
In this area, common practices for pond management are sun drying of the drained ponds, mechanical raking of the mud, lime application and slow filling with filtered seawater (98%). Most farmers (62%) use disinfectants before lime application. The most commonly used disinfectants are bleach and iodine, while other chemicals are used occasionally. Pond fertilization is not frequently practiced (24% of cases). Seawater is the main source of water for refilling and water exchange because freshwater sources are not available in the region; therefore, water exchange is seldom or not practiced at all and salinity generally increases. One respondent reported salinity values over 50 ppt.
The main cause of low yields was the white spot disease and the Taura syndrome. These diseases accounted for 73 and 65% of the reported production losses. Other important problems are bacterial diseases (50%); fungal (24%) and parasite infections (15%). Low yields, combined with a low world price for shrimp have pushed many farms into a situation where they are no longer profitable.
The results from the survey also show that 81% of the shrimp farms experienced production problems and many of these farms are considering alternative aquaculture species as an opportunity to stabilize production. Tilapia culture in shrimp ponds is being considered by 71% of the farmers. Three farms reported that they had tilapia in some of their ponds. However, none of the farmers reported any significant benefits or problems from the tilapia. The tilapia stocked were of unknown origin and were reported to be gray. This implies that they were not one of the red strains, which have been selected for salt tolerance. The two main constraints in Mexico for the development of tilapia as an alternative species for culture in shrimp ponds are knowledge of the biotechnologies required for culture in seawater and supply of seed of salinity tolerant strains of tilapia. This is a unique opportunity to continue harnessing the strengths of Aquaculture CRSP expertise and aid the development of a sustainable aquaculture system that would both safe- guard the jobs of many local inhabitants and provide work to low-income fishermen in coastal areas.