INTRODUCTION
The largest number of protected areas (PA) in the world is in Brazil 1, totaling more than 30000 Km2 (2. About 43% of Brazilian Amazon are considered PA 3. Although there are doubts about the purpose of conservation units, studies indicate that these are useful in reducing deforestation and ichthyofauna conservation 4,5.
The Amazon basin is home to the world’s largest ichthyofauna diversity 6,7. In the Madeira River basin, more than 820 species of fish were recently identified 8. In the Machado River basin, Madeira River sub-basin, 48 species were collected at the Pirarara and Tamarupa rivers 9, 140 species in small streams 10 and 74 species in the Tarumã river, middle Machado River 11. The studies on evaluation of fish stocks in the Amazon region are scarce 12, as well as information on fish morphometric relationships 13,14.
The length-weight relationship (LWR) has many functions in the area of fish ecology 15. The LWR allows i) to predict fish length based on weight and vice versa, ii) calculate the growth rate of the species and iii) obtaining the body state of the individuals sampled 16. The LWR studies are necessary to understand the fish life cycle, especially in regions where fishing represents the important economic activities and the main animal protein consumed by traditional communities 12. The objective of this study was to calculate the LWR of 13 species of fish captured in the Tarumã River, Jaru Biological Reserve, as the first study on the biology of fish species in this PA.
MATERIALS AND METHODS
The Jaru Biological Reserve (Rebio Jaru) is administered by the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio). The Rebio Jaru hydrographic network (9°27’19” S, 61°40’43” W - 9°47’04” S, 61°40’19” W) is part of the Machado River basin, Rondônia State, Brazil. The Tarumã River is located in the Rebio Jaru area.
We performed collections of freshwater fish in May and September 2015. We collected the fish using a total of eight gillnets with meshes of 2 x 20 m (mesh sizes: 30, 40, 50, 60, 70, 80, 90 and 100 mm, opposite knots), these were euthanized in a solution of clove oil 17. The fish were fixed in 10% formalin solution, preserved in 70% ethanol and later deposited in the Coleção de Peixes da UFMT, Brazil. The fish sampling was authorized by the ICMBio (license code: 48723-2/2015).
The individuals captured were identified with the help of identification keys 18 and biometric data (total length (TL) in cm and total weight (TW) in g) were recorded. Weight and length were estimated using the expression P = aC b , where P = weight total, C = total length, a = intercept and b = angular coefficient (18 Le Cren, 1951); the parameters a and b were estimated after logarithmic transformation of weight and length data 19. We verified in the fishBase 20 the absence of the LWR records, as well as the occurrence of the TL and TW maximum values recorded for the species captured in the Tarumã river. Statistical tests were performed using the R-package 21 with significance of p<0.05.
RESULTS
The LWR was estimated from 343 specimens belonging to thirteen species, seven families and two orders (Table 1). The linear regressions were significant (p≤0.001). The R2 varied from 0.91 in Boulengerella cuvieri to 0.99 in Brycon amazonicus. The intercept a varied from 0.0045678 in B. amazonicus to 0.0798564 in B. cuvieri (mean 0.0422121 ± 0.0532370). The value of b varied from 1.36 in Leporinus friderici to 3.30 in B. amazonicus (mean 2.33 ± 1.37). The specie Colossoma macropomum had an isometric growth pattern (b = 3.09) (Table 1).
DISCUSSION
The new LWRs for 2 species, new maximum weight for 4 species and maximum sizes recorded for 3 species highlight the scarcity of information on biological aspects of Amazon fishes. The allometric coefficients of the L. friderici, B. cuvieri, Prochilodus nigricans, Myloplus lobatos, Myloplus rubripinnis and Serrasalmus rhombeus species are not among the values (2.7-3.5) described by Froese 16. Factors such as habitat, area, seasonality, degree of stomach repletion, sex ratio, health, sample size, reproductive stages and preservation methods, could justify the values not in line with that proposed by Froese 16) (22,23,24. These results can provide information for the FishBase as well as important data for the management of icthyofauna and conservation of the Tarumã River Basin.