INTRODUCTION

The state of São Paulo has the largest remaining Atlantic Forest area, located mainly in state parks, ecological stations and Conservation Units (CU) ¹. The present work is part of an important UC known as the Ipanema National Forest, belonging to the sub-basin of the Ipanema River, which is part of the Sorocaba river basin. The length-weight ratio is an important parameter of fish populations and their applications range from estimating the weight and length of an individual to indications of fish condition (condition factor) ². The condition factor is an indicator of the health status of an individual and its value reflects the recent nutritional conditions and / or the spending of reserves on cyclical activities, analyzing the relationships with the environmental conditions and the behavioral aspects of the species ^3,4.

Given the above, the objective of this study was to present unpublished data on the weight-length relationship (LWRs) of two species Hypostomus ancistroides and Corydoras flaveolus sampled in rivers of the Ipanema National Forest.

MATERIAL AND METHODS

The Ipanema National Forest is a Federal Conservation Unit (CU) administered by the Chico Mendes Institute for Biodiversity (ICMBio), located in the municipalities of Araçoiaba da Serra, Iperó and Capela do Alto, covering an area of 5,385 ha of the Atlantic Forest biome, inserted in the Water Resources Management unit 10 (UGRHI 10), corresponding to the hydrographic basins of the Sorocaba river and the center of the Tietê ⁵.

The collection of samples was made in January and July 2013 within the Ipanema National Forest, belonging to the sub-basin of the Ipanema River, in the Tietê river basin, using a 50 by 50 cm sieve with a mesh of 1 cm and net of trawl of 3 meters in length and 5 mm mesh. After capture, the fish were euthanized in the field under the effect of the benzocaine anesthetic, after that they were weighed with the aid of on a digital balance (0,00001 g precision) and measured with the aid of a tape measure and analogical caliper (0,1 mm precision) and then placed in 10% formaldehyde solution for fixation. In the laboratory, the samples were transferred to alcohol 70% for preservation. The length-weight ratio for both species was based on Keys ⁶. Species identification was based on Smith et al ⁷, and all the collected vouchers were deposited in the fish collection at the Functional and Structural Ecology of Ecosystems Laboratory at Universidade Paulista, Sorocaba campus, São Paulo, Brazil (catalog numbers LEEF 0072-0073). All of the collections were carried out with authorization of the IBAMA license (Authorization N^° 658/2015).

In addition, the choice of the TL (total length) measure was adopted in the study, as it does not make the results generated unfeasible, taking into account the different types of length measures that can be used for studies of the length-to-weight ratio (LWR). The type of length used varies according to the study. In this work, we chose to use the total length, as it is a measure that includes the entire tail fin and all individuals sampled in this study had this structure intact. As an example, the following studies used the total length to calculate the RLT: ^8,9.

For the weight / length ratio, the formula was applied: Wt = a Lt b ¹⁰, where Wt corresponds to weight, Lt, length, a, the factor related to the degree of fattening of individuals and b, to the allometry coefficient, related to the growth of individuals. The values of a and b were estimated using the least squares method (predictive model), after logarithmic transformation in the Neperian base of the following equation: In Wt = In a + b In L t ¹¹.

RESULTS

A total of 91 specimens were captured, distributed in one orders (Siluriformes) and two families (Loricariidae and Callichthyidae, representing two species, 52 of Hypostomus ancistroides and 39 of Corydoras flaveolus (Table 1). Comparing the results of parameters a and b with the Baesian analysis, Hypostomus ancistroides presented measurements 0.0058 (0.0043-0.0072) which is outside of what is expected for parameter a, with the expected value for this parameter a=0.01862 (0.00977 - 0.03550), according to data Fish Base, while Corydoras flaveolus presented measurements 3.75 (3.38-4.11) which is outside of what is expected for parameter b, with that expected for this parameter b = 3.12 (2.943.30). New records of maximum length for both species were raised.

Table 1 Relationship of total length (cm) and weight (g) for the two species sampled in rivers of the Ipanema National Forest, where W = aLb and n = number of specimens used in the analysis, R2 = correlation coefficient. The length-weight ratios for the two species were significant in p<0.0. 

DISCUSSION

The individuals of the species Hypostomus ancistroides, a species described with specimens from the Sorocaba river basin ¹², presented, according to the Baesian analysis, that the parameter "a" is out of expectations, indicating that the body shape is atypical for the species in question ¹³, with a lower degree of fattening. The "b" factor of individuals of the Corydoras flaveolus species was 3.75, which is not in the 2.5 to 3.5 range, considered ideal ¹⁴, indicating that the species did not show an expected ideal growth. The size range covered for the Corydoras flaveolus was small (i.e 3.38 to 4.11 cm). Values less than or greater than 3.0 indicate individuals who, over the course of growth, become more "longilines" or "round", respectively. Therefore, the LWR for this species should be considered preliminary and needs to be verified in future studies.

These changes may be related to seasonal differences that may be affected by temporal variations in food availability, food activity, environmental factors (such as water temperature, salinity and nutrition), population density or sex that may affect the estimated values of the relationships obtained ^15,16.

Therefore, the weight and length ratio can also be used to assess the degree of well-being or health of the species through the condition factor, which may reflect recent nutritional conditions, expenditure of energy reserves, parasitic infections and others. This index can also indicate the reproductive period of species, periods of changes in diet and accumulation of fat, as well as seasonal changes in environmental conditions ^17,18.

Although the sample size of each species was relatively low, the r² values were considered acceptable for both species ¹⁹, with "b" values in the LWR between 3.04-3.27 and 3.38 -4.11, respectively (Table 1). Although easy to obtain, data on LWRs are scarce for several species in the Neotropical region, therefore, these data consist of important biological information for freshwater fish ²⁰.