Shrimp Farming and the Environment - Library

worldwide adopt a “high health” shrimp system similar to that advocated in the United States, but bothPruder and Chamberlain (1994) conclude that “high health” shrimp systems alone do not appear to be asolution for preventing outbreaks of Taura syndrome. Both conclude that to reach sustainableproduction and financial performance goals, there are no substitutes for good husbandry and effectivemanagement.In general, there is a danger in relying on SPR or SPF strains of shrimp. Experience shows that otherillnesses may infect such animals when they are exposed to pond environments which are less sterilethan where they were bred. The use of SPF or SPR strains requires close follow-up by a wellestablishedveterinary service. It may in fact be more important to implement such follow-up than tofocus on development of SPFs or SPRs. A cautious and broader-based approach is recommended, sinceit has not been convincingly documented that SPF or SPR strains of shrimp have a long-term advantageover “natural” shrimp.High-quality, pathogen-free feed supplyFeed has also been blamed as a source of infection in shrimp ponds. This may be a particular problemif “trash” fish and shrimp are used in feed. In general, this practice should be discouraged or, at aminimum, procedures for sterilizing feed components should be set in place.Optimal grow-out conditionsAs noted widely in the literature, poor husbandry and management make a significant contribution tothe susceptibility of shrimp to disease, and hence to its rapid development and spread. Of particularimportance are the maintenance of suitable water quality and the provision of high-quality feed in thecorrect quantities at the correct times. Effective training and information dissemination, coupled withappropriate incentives, are required to achieve this. A review of practical measures to prevent and treatdisease in shrimp ponds can be found in AAHRI’s book (Chanratchakool, Turnbull, et al. 1996).Farmer competence in the rapid identification and correct treatment of diseaseEarly identification and treatment of disease is essential to prevent disease spread. Correct and timelytreatment will also reduce the environmental impact of many of the chemicals and medicines used indisease control. Farmers need the knowledge to identify diseases themselves, as well as ready access tolaboratory diagnostic and advisory services. Although companies may play a role, there is a clear needfor government intervention to ensure quality control and to reduce the overuse of antibiotics and othercompounds.Increased species and system diversityDisease is likely to spread more rapidly, and its impact on local economies will be more severe, ifmonocultures of shrimp are grown. Mixed cropping (i.e., different species in different ponds), alternatecropping of different species in the same pond, and polyculture and integrated farming systems may allcontribute to this objective, and may be suited to different development contexts. In practice, manyfarmers will prefer the simplicity and the potential high returns from monoculture of shrimp, andeconomic incentives or regulations may be needed to encourage greater diversity in culturing.Cautious intensificationDisease has been widespread in all shrimp farming systems, from extensive to intensive. However, it islikely that the risk of disease increases in more intensive systems, especially if knowledge andhusbandry skills are inadequate. The economic incentives to intensify may be extremely strong, andintensification is desirable in several respects. It is therefore essential that governments, shrimp farmerassociations, and corporations ensure that skills keep pace with intensification by providing appropriatetraining, information dissemination, and access to expertise through local aquaculture extension agents.If such measures cannot be implemented, it may be necessary to restrain intensification using suitabledisincentives.VaccinationIt is generally assumed that it is not possible to vaccinate shrimp against disease (Subasinghe 1995).One reason is that the immune systems of shrimp appear to have a “short-term memory,” which rendersthe vaccine ineffective after just a few hours (Söderhäll & Cerenius 1992). However, recent research32