Evaluation of the susceptibility of the shrimp Litopenaeus vannamei to vibriosis when exposed to agriculture pesticides

Abstract

Due to increasing stringency of environmental regulations, agricultural production systems have switched from persistent pesticides to products which degrade more rapidly. In spite of that, new pesticide products can affect non-target organisms by continuous exposure to non-lethal concentrations, producing alterations such as reduced growth rate, impairment of the defense mechanisms and increased susceptibility to viral and bacterial infections. Experiments were carried out using Litopenaeus vannamei, juveniles (approximately 1g), methyl parathion and Vibrio parahaemolyticus isolated from a diseased shrimp. Initially, oral LC₅₀ and LD₅₀ of injected bacteria were determined in the shrimp to provide the guidelines to the experimental design. For the final experiment, treatments applied were: 1) shrimp fed with pellets containing 14.043 µg of methylparathion per gram of feed for 10 days, which were injected intramuscularly with sterile saline solution on the fifth day; 2) shrimp fed with pellets containing 14.043 µg of methylparathion per gram of feed for 10 days, which were injected intramuscularly with V. parahaemolyticus on the fifth day; 3) shrimp fed with pellets containing acetonitrile (the solvent for methyl parathion) for 10 days, which were injected intramuscularly with V. parahaemolyticus on the fifth day; and 4)