Changes in blood parameters of hybrid tambacu fish parasitized by Dolops carvalhoi (Crustacea, Branchiura), a fish louse

Measurement of blood parameters has been used for many years as a tool for monitoring the health of fish. The present study investigated the effects of a natural infestation of Dolops carvalhoi Lemos de Castro, 1949, on red blood cells, thrombocytes and white blood cell counts, as well as plasma glucose and serum electrolyte levels in hybrid tambacu (Piaractus mesopotamicus x Colossoma macropomum). Parasitized fish showed low haematocrit and magnesium levels and increases in MCHC, plasma glucose levels, serum protein, sodium and chloride levels, number of monocytes and PAS-positive granular leukocytes (PAS-GL), when compared with values in control fish. This study is the first to report changes in fish physiology caused by D. carvalhoi infestation, and the results obtained indicate that a mild infection can lead to important osmoregulatory disturbances in hosts. key words: haematological, Dolops carvalhoi, blood cells, freshwater fish, infestation, parasites introduction The hybrid tambacu (male Piaractus mesopotamicus × female Colossoma macropomum) is a fish of great economic importance to Brazilian aquaculture. It is widely appreciated for sport and pleasure fishing and for fish farming, due to its quick growth and quick weight *Contact address: Dr. Marcos Tavares-Dias, Instituto de Saúde e Biotecnologia, Universidade Federal do Amazonas. Estrada Coari-Mamiá, 305, Espírito Santo, 69460-000, Coari, Amazonas, Brasil, Phone and Fax: +55 97 3561 2363; E-mail: [email protected]; mtavaresdias@ ufam.edu.br