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INTRODUCTION
The correlation between weight and length includes characteristics selected for the population, providing very important information about the specific population 1,2. Among the most frequent uses of the weight and length ratio, the possibility of indirect weight determination by length or vice versa, the indication of the condition of the fish, in relation to fat storage or even the indirect analysis of growth 3. The knowledge of quantitative aspects, such as a weight / length ratio, is of great importance for a better understanding of the role of environmental characteristics in the ecology of species, as well as tools for studies of fisheries biology, threats to the management and conservation of stocks, in addition to population development 4.
Given the above, the objective of this study was to present unpublished data on the weight-length relationship (LWRs) of two species Hisonotus francirochai and Roeboides descalvadensis sampled in rivers along the MS-163 highway in Mato Grosso do Sul.
MATERIAL AND METHODS
The state of Mato Grosso do Sul is drained by two sub-units of the Prata basin - the Upper Paraná basins to the east and the Paraguay basin to the west 5, belonging to the Upper Paraguay basin, one of the main basins of the Central-West Region of Brazil and to the Upper Paraná basin. The lenght-weight ratio is an important tool for describing fish growth and development, regardless of age 6. With this tool we can estimate the condition factor, used as an inference parameter of the health of the sample and its biomass in natural populations to analyze the relationships with the environmental conditions and the behavioral aspects of the species 7,8.
The samples were collected in January and July 2017 and January 2018 in rivers belonging to the state of Mato Grosso of Sul along the MS-163, using a 50 by 50 cm sieve and a 5 mm mesh, and a drag of three meters of mesh of 1 cm. 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 individuals were transferred to 70% alcohol for preservation and identified with the aid of identification keys and specialized literature 5. In this way, species were identified, and all collected specimens vouchers were deposited in the fish collection at the Laboratório de Ecologia Funcional e Estrutural de Ecosssistemas, Universidade Paulista, Sorocaba campus, São Paulo, Brazil (catalog numbers LEEF 0070-0071). All of the collections were carried out with authorization of the IBAMA license (Authorization N° 658/2015).
The length-weight ratio for both species was obtained based on Keys 9. Different types of length measurements can be used for length-weight relationship (LWR) studies. The most commons are total length, standard length and fork length. The type of length utilized vary according to study. In our case, we have chosen to use total length because is a measure that include the whole caudal fin and all the individuals sampled in this study presented this structure intact. In cases where the caudal fin presents damages, usually by predation or sampling methodologies, it is better use standard length. As example, the following studies have used total length to calculate LWRs: 10,11,12.
RESULTS
A total of 49 specimens were collected, distributed in two orders (Siluriformes and Characiformes) and two families (Loricariidae and Characidae respectively), being 31 of Hisonotus francirochai and 18 of Roeboides descalvadensis. The parameters of LWRs are summarized in Table 1.
Table 1 Total length (cm) and weight (g) ratio for the two species sampled in rivers along the MS-163 highway in Mato Grosso do Sul, 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.
For Hisonotus francirochai there is no published formula for TLxSL, to transform TL (total length) into SL (standard length), so it was not possible to confirm that the value found in TL is greater than the SL record. For Roeboides descalvadensis, there is a formula published and disclosed by FishBase: TL = 0+1.182 x SL, where the transformation was performed and the TL found is equivalent to 7.87 cm of SL, unfortunately smaller than the largest record (8.9 cm).
DISCUSSION
The values of parameter b of LWRs ranged from 2.88 to 2.97 (Table 1), which is adequate as demonstrated by Froese 13. Comparing the results with Fishes Bayesian LWR predictions 14, the two species are within what is expected for both parameters (a and b), even presenting slightly low values, which may be related to the smaller variation in size. The r2 values were considered acceptable for the species, even though they had a relatively low sample number (Table 1) 15.
Biometric variables and the type of growth of fish species can be influenced by several factors, such as food availability, population density, sex, physiology or abiotic factors that can affect the estimated values of use relationships 16,17,18,19. Therefore, more data, a larger sample size, is needed to confirm these growth values.
Although easily obtained, LWRs data are scarce for several species in the Neotropical region, thus, the results of this study contribute with biological information for the species studied in this work.
