BOLETIM DO INSTITUTO DE PESCA

The length-weight relationship of fish species is widely used in fisheries monitoring programs and it is an important tool for proposing stock management measures. The objective of this study was to estimate the growth parameters of 34 species belonging to the fish community captured by experimental fishery in the Três Irmãos reservoir, Tietê river. The biological and ecological characteristics of these species are also presented in order to understand the profile of the present fish community. The fish were collected during ten experimental fishing seasons between October/2015 and February/2018, with quarterly frequency using four types of fishing gear. All fish captured were identified and the total length TL (cm), standard length SL (cm) and total weight TW (g) were measured. The length-weight relationship was established using the linear regression TW vs SL (log-transformed): log (TW) = log (a) + b log (SL), where a is the regression curve intercept (coefficient related to body shape) and b is the coefficient of regression (exponent indicating the type of growth). A total of 7,319 individuals was identified, comprising five orders: Characiformes (7 Families), Siluriformes (5 Families), Perciformes (1 Family), Cichliformes (1 Family) and Cyprinodontiformes (1 Family). The most abundant species were Plagioscion squamosissimus (N=1,513), Geophagus sveni (N=1,160), Serrasalmus maculatus (N=1,049) and Metynnis maculatus (pacu-CD) (N=974), all of them being target species for professional artisanal fishing, with the exception of pacu-CD, which is discarded since it has no commercial interest. From the whole set of analyzes 15 species (44.1%) have positive allometric growth type (3.15≤ b ≤3.59), 14 (41.2%) isometric (2.98≤ b ≤ 3.08), and 5 (14.7%) negative allometric growth (2.7 ≤ b ≤ 2.90). Among the species studied nine reached a maximum length above that of the FishBase: Cichla piquiti (TL= 55.4 cm), Crenicichla haroldoi (SL= 21.5 cm), C. jaguarensis (SL= 23.5 cm), Cyphocharax nagelii (TL= 22.9 cm), Hypostomus ancistroides (TL= 28.5 cm), Metynnis maculatus (TL= 19.5 cm), Piaractus mesopotamicus (SL= 60.0 cm), Roeboides descalvadensis (SL= 11.3 cm) and Schizodon borellii (TL= 40.0 cm).


INTRODUCTION
The Length-Weight Relationship (LWR) of fish species is widely used among fisheries scientists in fisheries monitoring programs.It is an important tool for proposing stock management measures since it provides information on the autecology of species (Vazzoler, 1996).Often there is a need to estimate the size of a fish population in a given water body, in order to accomplish sustainable exploitation of the fish resources (Le Cren, 1951;Pauly, 1984;King, 1995;Froese, 2006).In addition, the Length-Weight Relationship can also be used for estimating biomass from fish length frequency data, and as a measure of the length-weight variation of individuals, indicating their condition or well-being (Petrakis and Stergiou, 1995).
Several researches on the monitoring and exploitation of fisheries resources focus on the marine environment (e.g., Beverton and Holt, 1957;Ricker, 1958;Gulland, 1969).In Neotropical freshwater environments, these studies are relatively more frequently in rivers (Bayley, 1981), when compared with reservoirs (Gubiani et al., 2009).In general, there is a shortfall in the knowledge about the Length-Weight Relationship of Neotropical freshwater fishes (Azevedo-Santos et al., 2017).For reservoirs, mainly in Brazil, is clear the needs of new studies in this scope.For instance, for the upper Paraná river, which hold a series of reservoirs (see Agostinho et al., 2008), just a few works were published (e.g., Benedito-Cecílio et al., 1997;Angelini and Agostinho, 2005;Gubiani et al., 2009;Oliva-Paterna et al., 2009;Marques et al., 2016).
The present work has the main objective to estimate the growth parameters of fish species captured by experimental fishery in the Três Irmãos reservoir, low Tietê river basin.The biological and ecological characteristics of these species are also presented in order to understand the profile of the present fish community.

MATERIAL AND METHODS
The Três Irmãos reservoir is located in the Northwest region of the State of São Paulo, between the municipalities of Pereira Barreto and Andradina.Its construction started in 1980, being finished in 1990.With a flooded area of 757,000 ha. is the largest and last reservoir for hydroelectric energy production in Tietê River.It receives contribution from eleven tributaries, among them the Pereira Barreto Channel, an important connection to the São José dos Dourados River, SP (CESP, 1998;Castro et al., 2018) (Figure 1).
The fish samples were obtained from October/2015 to February/2018, quarterly, in sites with three different environments characteristics (lotic, lentic and transition), under the project "Monitoring the aquatic environment of the Três Irmãos Reservoir" supported by Tijoá Participações e Investimentos Company.
The fish were captured using gill nets, with mesh size of 3,4,5,6,7,8,9,10,12,14,16,18 and 20 cm between opposing nodes, with stretched mesh, and height ranging from 1.50 to 2.50 meters, 20.00 meters of length each, and total network area of 504.8 m 2 .The net sizes were defined according to the characteristics of the sampled environments (lotic, lentic and intermediate) and the mesh sizes as commonly used by fishermen in the region.The immersion period of the gill-net was 24 hours, with expenditure every 12 hours.To complement the ichthyofauna 3/10 survey of the region, the fishing with rod (line and hook), casting net and sieve, were also used.
The fishes were classified by mesh size, identified at the lowest possible level, their total length (TL) and standard length (SL) measured with an ictiometer (scale in millimeters), and the total weight (TW) of each specimen obtained from an electronic weighing-machine with a minimum of 1g scale.Measurements and weighing of all species collected were carried out with the specimens preserved in natura.Two specimens of each species (vouchers) were deposited in a scientific or didactic collection at the Laboratory of Ecology and Continental Fisheries (LabEcoPesca) of the Fisheries Institute, in São Paulo, Brazil.
For the length-weight relationship (LWR) was applied the potential equation TW = a * SLb, where TW is the total weight, SL the standard length, a the factor related to the degree of fattening of the individuals and b (ø) the coefficient of related to the shape of individuals' growth.
The values of a and b were estimated by the least squares method (predictive model), after logarithmic transformation of the following equation: log (TW) = log (a) + b * log (SL), where a is the curve intercept (coefficient related to body shape) and b the regression coefficient (exponent indicative of growth type).The coefficient of determination r² was used as an indicator of the linear regression fit quality (Zar, 1984).Prior to regression analysis, log10-log10 plots of TW and SL were used to detect and exclude outliers (Froese, 2006).
The species growth was considered isometric when the value of b = 3 and allometric when this value was lower or higher than 3 (b <3 <b or b <3, b> 3).Student's t-test was used to verify if the parameter b was significantly different than expected or from the theoretical value (b = 3, p <0.05).Thus, ts = (b-3) / sb (Zar, 1984), where ts-Student t test; b = slope, sb = slope standard error.Where sW = variance of body weight (g), sL = variance of standard length, n = sample size.All statistical analyzes were considered significant at the 5% level (p <0.05).
For the origin identification of the species, the classification contained in Langeani et al. (2007) was followed.For the categorization of size, we used the classification of Vazzoler et al. (1997), according to the description: size G > = 40 cm of total length (TL); size M > 20 and < 40 cm of TL.The values of TL were transformed to SL by the simple linear regression equation for each species analyzed: SL = a + bTL.In order to classify the trophic structure of the fish community present in the Três Irmãos reservoir, the studies of Vazzoler et al. (1997), Graça e Pavanelli (2007), and Langeani and Rêgo (2014) were considered.
For the analysis of the reproductive strategies, we based the criterion adopted in the studies carried out in the Alto Paraná basin and summarized by Vazzoler (1996), Vazzoler et al. (1997) and Suzuki, et al. (2004).The length of first sexual maturation (L50%) of the analyzed species was obtained based on published works for the neotropical region (Table 2).
The present work, inserted in the project (SGP nº 1305) "Diagnosis of the fish fauna of the Três Irmãos reservoir, lower Tietê river basin", was approved by the Institutional Ethics Committee (CEEAIP) under No. 08/2016.

DISCUSSION
Knowledge of existing fish species in a river basin is the minimum condition necessary for the implementation of any protecting measure both for water and fishery resources (Holzbach et al., 2005).The results presented in this study can contribute to the current knowledge of the parameters the Lengh-Weight Relationships (LWR) of fish species present in the Três Irmãos reservoir, located in the lower Tietê river basin.Such information can benefit fishery scientists in the fishery diagnoses and management.The LWR is an excellent monitoring tool in commercial fishing landings (King, 1995;Gubiani et al., 2009;Vaz-dos-Santos and Gris, 2016), and weight is a good estimator of fish welfare or condition in a given environment (Vazzoler, 1996).
The captured fish assembly consisted mainly of adult fish, since most species were already over the length of first sexual maturation (L50%) (Table 2), based on estimates of L50% obtained in other studies (Braga, 1997;Vazzoler et al., 1997;Barbieri et al., 2000;Suzuki, et al., 2004;Luiz et al., 2011), and by the smallest mature individual identified in the sample (Langeani and Rêgo, 2014).
The proportion of imature/mature was higher only for Piaractus mesopotamicus (54.5%/45.5%)and Plagioscion squamosissimus (58.7%/41.3%)(Table 2), indicating that pacu, a migratory and autochthonous species in this basin, has reproduced in a lentic/ transition environment, despite its characteristics of lotic habits and of the piracema event (Table 3).The high proportion of immature specimens of P. mesopotamicus may be influenced by the systematic introduction of young fish in the reservoir by the hydroelectric concessionaires.However, the confirmation of this fact is necessary through studies of eggs and larvae in tributaries of the Três Irmãos reservoir; and genetic studies.Regarding the curvina/pescada-do-piauí, an allochthonous species from the Amazon basin, of lentic habits, the highest proportion of immature individuals shows that the specie is well adapted to this environment, finding favorable areas for reproduction and growth (Tables 2 and 3).These attributes has promoted the increase of commercial and recreational/sport fishing (Agostinho et al., 2007;Castro et al., 2018).However, despite the positive social/economic impacts on the fisher population, it is necessary to investigate the ecological impacts of this carnivorous/piscivorous species on native sedentary species in this environment, aiming at the best balance in the conservation and use of fishery resources, over the years.
The growth parameter value of b=3.62 for Apareiodon affinis (n=155) was outside to limits of 2.5 to 3.5 (Bagenal and Tesch, 1978).According to Calender, apud Gubiani et al. (2009), values of b< 2.5 or b>3.5 are often a consequence of small sample size and size range.In this case, for this species, such justifications are not adequate since A. affinis was well represented in number and size range.Although P. mesopotamicus sampling was small (n = 11), it did not affect the growth parameter for this species (b = 3.0) possibly due to the wide range of sizes sampled (A) (18.0-60.0cm SL), also it presented a good fit quality (r 2 = 0.99).The other species (Table 2) were within the limits recommended by Bagenal and Tesch (1978).
The maximum lengths (SL) reached in this study were higher than those observed in the Porto Primavera reservoir by Marques et al. (2016) for C. piquiti (SL = 49.5 cm) and C. nagelli (SL = 19.5 cm).Samples of P. mesopotamicus, C. haroldoi and H. ancistroides captured in Três Irmãos reservoir presented higher maximum sizes than those obtained in Gubiani et al. (2009) for 30 neotropical reservoirs.
For the length-weight relationship (LWR), the value of the parameter b depends on the shape and fatness of the fish species.The parameter b may vary temporally and spatially (Bagenal and Tesch, 1978).Thus, the LWR in fish is affected by a number of factors, including gonad maturity, sex, diet, stomach fullness, health, and annual differences in environmental condition, as well as season and habitat (Le Cren, 1951;Pauly, 1984;Froese, 2006).
Values of b = 3 indicate that the fish grow isometrically, while values of b ≠ 3 indicate allometry in the growth of the species.When the value of b> 3 the type of growth of the species is allometric positive, that is, the increase in weight is greater proportionally than its growth in length.If b <3, the growth is negatively allometric, the species grows more in its length then in weight (Benedito-Cecílio et al., 1997).A total of 14 fish species exhibited isometric growth, 15 positive allometric growth, and 5 allometric negative.The parameter b varied between 2.71 and 3.62.According to Froese (2006), b <2.5 indicates that the growth in length of a species is proportionally greater than its growth in weight; on opposite way, b> 3.5, the growth in weight is proportionally greater than its length.
Considering the ecological and behavioral characteristics of all species captured (Table 3), it is noticed a composition mostly of native species, with medium and large size.The majority is sedentary, with partial spawning, and most without parental care, with carnivorous and omnivorous eating habits.However, although the lower number of non-native species (n=14; 41,2%), abundance and biomass, by species is higher than for all native species present in commercial and experimental (scientific) fishing (Castro et al., 2018).The migratory species showed low abundance and higher biomass, represented by four 9/10 species: Leporinus friderici (piau-de-três-pintas), Prochilodus lineatus (curimbatá), Pimelodus maculatus (mandi-guaçu) and P. mesopotamicus (pacu-guaçu) (Table 1).

CONCLUSION
This study represents contribution for length-weight relationships in dammed environments in the Southeastern region of Brazil, which can be useful for comparisons with similar data from other Brazilian reservoirs.The LWR is an excellent monitoring tool in commercial fishing landings, as it can benefit fisheries scientists in the elaboration of diagnostics and fisheries management when information is only length and not weight.

Figure 1 .
Figure 1.Map of the studied region, with emphasis on the Três Irmãos reservoir, in the lower Tietê river basin, São Paulo, with its down and upstream dam, neighboring municipalities, and sampling site: JNA-downstream from the Nova Avanhandava dam; JAC-Jacaré Stream; PBA-Pereira Barreto; JTI-downstream of the Três Irmãos dam.

Table 1 .
Total length (cm), standard length (cm) and total weight (g) characteristics for 34 species caught in Três Irmãos reservoir, during October/2015 and February/2018.Data marked in gray indicate values higher than those available in the revised literature.

Table 2 .
Parameters of the relationship between standard length (cm) and total weight (g) for 34 species caught in Três Irmãos reservoir, during October/2015 and February/2018.

Table 3 .
Summary of the biological, ecological and behavioral characteristics of the species sampled for the reservoir of Três Irmãos, Tietê river, from October/2015 to February/2018.