Revista Chilena de Historia Natural 76 (1): 3-14, 2003
RESEARCH ARTICLE
Spatial and temporal variations of the fish assemblage of a low order fluvial system from
central-south of Chile
The Nonguén stream (order 3) is a lower zone tributary of the Andalién river coastal
mountain basin (Bio-Bío region) which displays a marked difference between its rithral sector (well-conserved and with a secondary
Nothofagus forest) and its potamal area (urbanly-used and organically polluted waters). This contrast could imply an
alteration in the normal pattern of Chilean ichthyofauna, as described for a variety of fluvial systems in the country: a downstream
increase in numbers of species, individuals, and diversity downstream, as well as increased corporal sizes of individuals in the lower
zones of the river. Species composition of fishes of the Nonguén stream and their community patterns along the fluvial system within
an annual cycle have been studied. The results show a high number of species in the lower parts, i.e. four species in the rithron and
ten in the river mouth. The diversity, abundance and distribution of the fishes varied according to the season of the year, reflecting
displacements associated with the fauna’s ontogeny, reproduction and feeding. The sampling stations of the middle and lower zones of
the river presented an assemblage with smaller individuals than those found at the head of the river, with the consistent dominance of
larger salmonidae in the upper zone. Accordingly, it is suggested that: (i) the alteration of the potamal area does not significantly modify
the characteristic patterns of ichthyofauna in fluvial systems, and (ii) the Nonguén stream is a reproduction and growth system for
juveniles of both native and introduced species which make up permanent associations in the fluvial system.
Key words:
ichthyofauna, diversity,
streams, spatial-temporal variations, assemblage, fluvial system
