The physiology of the Tambaqui ( Colossoma macropomum ) at pH 8.0
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ORIGINAL PAPER
The physiology of the Tambaqui (Colossoma macropomum) at pH 8.0 Chris M. Wood1,2,3,4 · R. J. Gonzalez5 · Márcio Soares Ferreira4 · Susana Braz‑Mota4 · Adalberto Luis Val4 Received: 14 August 2017 / Revised: 5 November 2017 / Accepted: 17 November 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017
Abstract The Tambaqui is a model neotropical teleost which is of great economic and cultural importance in artisanal fisheries and commercial aquaculture. It thrives in ion-poor, often acidic Amazonian waters and exhibits excellent regulation of physiology down to water pH 4.0. Curiously, however, it is reported to perform poorly in aquaculture at pH 8.0, an only slightly alkaline pH which would be benign for most freshwater fish. In initial experiments with Tambaqui of intermediate size (30–50 g), we found that ammonia excretion rate was unchanged at pH 4, 5, 6, and 7, but elevated after 20–24 h at pH 8, exactly opposite the pattern seen in most teleosts. Subsequent experiments with large Tambaqui (150–300 g) demonstrated that only ammonia, and not urea excretion was increased at pH 8.0, and that the elevation was proportional to a general increase in MO2. There was an accompanying elevation in net acidic equivalent excretion and/or basic equivalent uptake which occurred mainly at the gills. Net N a+ balance was little affected while C l− balance became negative, implicating a disturbance of Cl− versus base + exchange rather than N a versus acid exchange. Arterial blood pH increased by 0.2 units at pH 8.0, reflecting combined metabolic and respiratory alkaloses. Most parameters recovered to control levels by 18–24 h after return to pH 6.0. With respect to large Tambaqui, we conclude that a physiology adapted to acidic pH performs inappropriately at moderately alkaline pH. In small Tambaqui (4–15 g), the responses were very different, with an initial inhibition of ammonia excretion rate at pH 8.0 followed by a subsequent restoration of control levels. Elevated ammonia excretion rate occurred only after return to pH 6.0. Furthermore, MO2, plasma cortisol, and branchial vH+ATPase activities all declined during pH 8.0 exposure in small Tambaqui, in contrast to the responses in larger fish. Overall, small Tambaqui appear to cope better at pH 8.0, a difference that may correlate with their natural history in the wild. Keywords Alkalinity · Ammonia · Urea · Oxygen consumption · Nitrogen quotient · Acid–base regulation · Ionoregulation
Introduction The Tambaqui (Colossoma macropomum), a serrasalmid teleost which is native to the Orinoco and Amazon river watersheds, is now extensively exploited in both aquaculture and capture fisheries, and is quickly becoming a model neotropical species in physiology (reviewed by Goulding and Carvalho 1982; Araujo-Lima and Goulding 1997; PradoLima and Val 2016; Wood et al. 2017; Da Silva Nunes et al. 2017). The Tambaqui is renowned for its robust physiology, and is particularly resistant to the hypoxic and acidic conditions which are typical of these
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