Tolerance response of tambaqui Colossoma macropomum (Cuvier) to water pH Paulo Henrique Rocha Aride 1 , Rodrigo Roubach 2 & Adalberto LuisVal 3 1 UniNilton Lins, PRPPG, Manaus, AM, Brazil 2 Coordenac° a ì o de Pesquisas em Aquacultura/CPAQ, Instituto Nacional de Pesquisas da Amazo Œ nia/INPA, Manaus, AM, Brazil 3 Laborato¤ rio de Eco¢siologia e Evoluc° a ì o Molecular/LEEM, Instituto Nacional de Pesquisas da Amazo Œ nia/INPA, Manaus, AM, Brazil Correspondence: Paulo H R Aride, UniNilton Lins, Manaus, AM, Brazil. E-mail: paride@niltonlins.br Abstract Tambaqui Colossoma macropomum (Cuvier) is a ¢sh of primary importance in Amazon aquaculture. It has been described as an acid-resistant species that moves seasonally between white (muddy) water and black water rivers and enters the extremely dilute acidic areas of £ooded jungle to feed during the rainy season. To analyse the pH tolerance of this species, tambaqui were exposed to three water pH levels for 40 days (pH 4.0,6.0 and 8.0). The water was acidi¢ed slowly over 3 h, allowing the ¢sh to acclimate. A simi- lar protocol was used to adjust water pH to 8.0. No mortality was observed during the exposure period. Several haematological parameters were signi¢- cantly changed in alkaline-exposed animals, with signi¢cant decreases in haematocrit (20%), haemo- globin concentration (8%) and red blood cells (12%). Tambaqui showed severe blood variations when ex- posed to alkaline pH. Fish ¢nal weight, condition fac- tor and speci¢c growth rate (SGR) was inversely proportional to a pH increase, and SGR were higher for ¢sh reared in acidic water. The relative insensitiv- ity of tambaqui to low pH con¢rms its acid tolerance and is in accordance with its natural occurrence in black water habitats. Keywords: Amazon, ¢sh, tambaqui, pH, tolerance, blood Introduction The Amazon basin is the largest £uvial system in the world, draining about 37% of continental South America (Sioli 1984). Three main water types occur in the Amazon: white (muddy) water (pH 6.2^7.2), black water (pH 3.8^4.9) and clear water (pH 4.5^ 7.8). Seasonal and daily variations in water pH levels are an important environmental factor a¡ecting ion homeostasis in ¢sh of the Amazon (Matsuo & Val 2002). Extreme water pH represents a challenge for many ¢sh species and can limit their growth (Aride, Roubach & Val 2004), which is relevant to local pro- ducers. In the Amazon, ¢sh encounter naturally acidic, ion-poor waters, re£ecting the geochemistry and continuous input of humic and fulvic acids from the breakdown of jungle vegetation (Wood, Wilson, Gonzalez, Patrick, Bergman, Narahara & Val 1998), as well as neutral waters, such as the white waters, and alkaline waters that occur in £ooded areas and in ¢sh culture ponds. An increase in environmental pH a¡ects osmore- gulation in ¢sh and has been associated with an increase in mucus secretion (Wood et al . 1998). Increased pH also a¡ects oxygen transfer to tissues (Freda & McDonald 1988). Rainbow trout Oncor- hynchus mykiss (Walbaum) exposed to acid water ex- perience an increase in haematocrit, haemoglobin and red blood cell counts, a consequence of haemo- concentration caused by water dislocation (McDo- nald & Wood 1981). Wilson, Wood, Gonzalez, Patrick, Bergman, Narahara and Val (1999) described a signi- ¢cant net ion loss and physiological disturbance in three species of Amazonian ¢sh [Colossoma macro- pomum (Cuvier), Brycon erythropterum ( B. amazonicum) (Cope) and Hoplosternum littorale (Hoedeman)] exposed to extremely acidic waters. Tambaqui have been described as being acid resistant, and their ability to maintain homeostasis in acidic water was described by Wood et al . (1998), who exposed Aquaculture Research, 2007, 38, 588^594 doi: 10.1111/j.1365-2109.2007.01693.x r 2007 The Authors 588 Journal Compilation r 2007 Blackwell Publishing Ltd