Length at first sexual maturity of economically important fishes in the Brazilian Northeast Coast

Editor: Rubens M. Lopes Research involving fish stocks' reproductive aspects has social, economic, and biological importance; (Pinheiro, 2010; Véras and Almeida, 2016). Studies dealing with mean fish length at first sexual maturity are essential to assess and manage the exploited fish population and determine the minimum permissible size for capture, since some marine species have been overfished (King and McFarlane, 2003; Chellappa et al., 2010). According to Pinheiro (2010), the mean length at first sexual maturity represents the mean fish size when 50% of the individuals are ready to enter a new cohort, actively participating in the reproductive process. This work's objective was to estimate the mean length at first sexual maturity of economically important fishes in the Brazilian Northeast coast, thus improving the biological understanding of these species in the light of more efficient stock management. Samples from the following species were captured from 2013 to 2019, through artisanal fishery brought to the municipality of Raposa, in the state of Maranhão, Brazil (Figure 1): Genyatremus luteus (478 individuals 182M; 296F), Micropogonias furnieri (190 individuals 107M; 83F), Oligoplites palometa (172 individuals 97M; 75F), Nebris microps (95 individuals http://dx.doi.org/10.1590/S2675-28242020068311

Research involving fish stocks' reproductive aspects has social, economic, and biological importance; (Pinheiro, 2010;Véras and Almeida, 2016). Studies dealing with mean fish length at first sexual maturity are essential to assess and manage the exploited fish population and determine the minimum permissible size for capture, since some marine species have been overfished (King and McFarlane, 2003;Chellappa et al., 2010). According to Pinheiro (2010), the mean length at first sexual maturity represents the mean fish size when 50% of the individuals are ready to enter a new cohort, actively participating in the reproductive process.
This work's objective was to estimate the mean length at first sexual maturity of economically important fishes in the Brazilian Northeast coast, thus improving the biological understanding of these species in the light of more efficient stock management.
Samples from the following species were captured from 2013 to 2019, through artisanal fishery brought to the municipality of Raposa, in the state of Maranhão, Brazil ( The following data were collected: total (Lt), and furcal (Lf ) lengths (mm), total (Wt), and eviscerated (We) weights (g). Lengths were measured using a ruler, and weights were determined with a balance with a precision of 0.01 g. The fishes were longitudinally cut in the ventral part to remove the gonads, which were fixed in a 5% formalin solution for subsequent preservation in 70% ethanol.
The determination of young and adult specimens was done by verifying the gonad sexual maturity level according to the stages suggested by Brown-Peterson et al. (2011) andLowerre-Barbieri et al. (2011).
The mean fish length at first sexual maturity (L50) was estimated from the accumulated curve of the frequencies of occurrence of adult specimens per length class fitted to a logistic function. The fish maturation stages were grouped in young (stage A) and adult (stages B, C, and D). The immature stage (A) was similar in both sexes characterized by the small size and light color of the gonads. The development stage (B) had a larger size than the previous one and by the macroscopic visualization of blood vessels and small oocytes. The spawning stage (C) presented larger-sized gonads with prominent blood vessels. When gonads were in the regressing stage (D), they had darker coloration and flaccidity. The percentage of mature fish per length class was calculated and considered as dependent variable (Y), and the total length as an independent variable (X). Subsequently, the values were fitted to a logistic curve, according to the formula: Where P is the proportion of mature specimens, r is the curve slope, L is the length, and Lm is the mean length at sexual maturity. The total length (Lt) of the specimens evaluated was used as a morphometric measure for the calculations. Protocol 037/2018 of the Ethics Committee on animal use of the State University of Maranhão was respected.
The estimated L50 showed that most of the species presented maturing females, with sizes relatively larger than males (Table 2). However, P. crenulatus and S. setapinnis showed an opposite trend, probably because of the lack of selectivity of the fishing gears used in the captures. Based on the maturity size, management measures for these stocks should be considered by establishing a permissible capturing size. The number of specimens captured below the L50 was relatively low for all species evaluated, compared to mature fishes.