The condition factor of fishes from two river basins in São Paulo state , Southeast of Brazil

This work describes the relative condition factor of the Hypostomus strigaticeps, Astyanax altiparanae, Astyanax scabripinnis, Astyanax fasciatus, Astyanax sp1., Characidium aff. zebra, Piabina argentea, Hypostomus ancistroides, Hypostomus sp1., Parodon tortuosus, Serrapinus heterodon, and Bryconamericus sp., of the APA of São Pedro and Analândia (22°-23°S and 47°30’-48°30’W). The condition factor provides information about the physical state of the animal in the environment. In order to compare different species, the relative condition factor was used. Variations in this factor were correlated with variations through the year and with subsequent alterations in the physiological state of the fishes. The relative condition factor was shown to be efficient in indicating changes in fish condition throughout the year.


Introduction Introduction Introduction Introduction
One important derivative of growth is the condition factor or ponderal index, defined by the expression K = W/L 3 , where W = weight, L = length.Another means to define it is K = W/L b , where b is given from the weight/length relationship, expressed by W = aL b (Braga, 1986).Le Cren (1951) showed that the condition factor can be described by K = W/aL b or K = W/W´, and called it "relative condition factor" (K n ), where aL b is equal to the weight/length relationship.
The condition factor indicates the fish welfare in the habitat.To compare species of different sizes, the relative condition factor was considered the best index (Bolger and Connolly, 1989).According to these authors, changes in the condition factor based on length-weight relationships reflect seasonal alterations in the metabolic balance, maturation patterns and stomach repletion.
The aim of this work was to characterize the relative condition factor of some fish species from Acta Scientiarum.Biological Sciences Maringá,v. 27,no. 1,Jan 1).
At each sample point, individuals were collected using gill nets with mesh sizes of 1.5; 2.0; 2.5, and 3.0 cm, measured between adjacent knots (5 m long and 1.5 high).In addition to the nets, whenever possible, purse seines with a mesh size of 1.5 cm (1.5 m high), sieves, and traps were also used.
Fish effort was standardized, keeping time and the quantity of instruments employed at each point constant.Afterwards, specimens were put in plastic containers containing 10% formalin.Each container was labeled with the date and sample site.Fishes were identified in the laboratory up to the lowest taxonomic level.Each individual was measured: total length (cm), standard length (cm) and total mass (g).The relative condition factor was estimated for the most abundant species occurring in both studied basins.In the Corumbataí basin, the following species were analyzed: Hypostomus strigaticeps (Regan, 1908) The weight/length and condition factor were analyzed according to Santos (1978) andBraga (1986).Weight-length relationship was estimated for each species according to the expression W = aL b , where W = weight, L = length, a = intercept, and b = regression coefficient.The parameters a and b were estimated after mass and length were logtransformed and subsequent line adjustment using the criterion of least squares.
The relative condition factor was also evaluated.It is given by: K=W/W´, where W is the fish mass and W' is the mass estimated by W = aC b .The relative condition factor was used to compare species.Considering W and W' by species group, it is possible to compare the condition factor among them (Le Cren, 1951).

Results and discussion
The parameters a (intercept), b (regression coefficient), r (correlation coefficient), and N (number of specimens analyzed) of the lengthweight relationships are shown in Table 1.
The variation of relative condition factor was greater in the Corumbataí basin (Figure 2).
The species Hypostomus strigaticeps, Piabina argentea, Hypostomus ancistroides, and Parodon tortuosus, from the Corumbataí basin, exhibited the lowest values of relative K in August, which coincided with the period before reproduction, when gonads initiate their development.Furthermore, this is the coldest period of the year and fishes diminished foraging intensity.The reproduction peak of Hypostomus aff.plecostomus at Monjolinho Dam occurred in the spring (Barbieri and Santos, 1987), with the condition factor indicating the spawning period (Barbieri and Verani, 1987).
The species Astyanax altiparanae showed the lowest value in December (summer), when reproduction occurred.The low value of relative K in June for Astyanax scabripinnis may indicate a drop in foraging activity in the winter.In these characids, reproduction occurs during spring and summer, with a decrease in the stomach repletion index and accumulated fat during the winter (Nomura, 1975;Barbieri et al., 1982;Rodrigues et al., 1989).
The species Characidium aff.zebra showed the most variable relative K values in the six analyzed periods (February, April, June, August, October, and December).The two greater drops occurred in April and October, showing a decrease in foraging activity in the winter and the reproductive period in the spring (Figure 2 The condition factor may be influenced by the developmental stage of the gonads and by the degree of stomach repletion (Barbieri et al., 1982;Barbieri, 1989).Thus, it is a good indicator of the spawning period and can also indicate changes in population density, foraging conditions (Braga, 1986), and occurrence of seasonality in the environmental conditions (Braga et al., 1985).
The variation of the relative condition factor was more homogeneous in the Jacaré-pepira basin (Figure 3).
In the Jacaré-Pepira basin, the species Hypostomus strigaticeps and Hypostomus sp1.exhibited the lowest values of relative K in April (winter), which could be explained by a drop in foraging intensity.
The species Astyanax altiparanae and Astyanax fasciatus showed drops coinciding with the winter (decrease in foraging activity) and spring (reproduction peak).
Astyanax sp1.showed a variable relative condition factor throughout the analyzed period, with low values in April and October.Spawning peaks in this species occur during the autumn and winter.This fact could explain the low value in April (winter), but the reason for the drop in October (summer) remains unknown (Figure 3).The relative condition factor was shown to be an efficient instrument and indicates changes in fish condition throughout the year, and can also be used to indicate spawning period and/or decrease in foraging activity.
./March, 2005 two protected areas in the cuestas of São Pedro and Analândia, São Paulo State, Brazil.Variations in the relative condition factor were correlated through the year and among the species.