Stages of gonadal development and mean length at first maturity of wild females of white shrimp (Litopenaeus schmitti - DECAPODA, PENAEIDAE) in southern Brazil

Abstract

The stages of gonadal development for the female of white shrimp (Litopenaeus schmitti (Burkenroad, 1936)) were characterized based on histological analysis. Four stages (immature, developing, ripe and spawned) were determined according to the structure and arrangement of cells in the ovary. Each stage corresponds macroscopically to a characteristic color, except stages I (immature) and IV (spawned), in which colors are very similar and can be distinguished only microscopically. The chromatic scale varies from white/translucent (stage I), gray/green (developing), dark green to black (ripe). The mean size of cells was 54.01 µm (±3.5) (stage I), 136.80 µm (±8.8) (stage II) and 199.80 µm (±6.4) (stage III). The size frequency of cells was polymodal, and different cell stages were observed in ripe ovary, suggesting the occurrence of multiple spawning. The smallest ripe female measured 146 mm and the largest 180 mm of the total length. Estimated mean length at first maturity was 152 mm and the length at which 100% of females are mature is 170 mm. KEY WORDS:Litopenaeus schmitti, shrimp, reproduction, gonadal histology, length at first maturity RESUMO Os estágios de desenvolvimento das gônadas das fêmeas do camarão-branco (Litopenaeus schmitti (Burkenroad,1936)) foram caracterizadas por análise histológica. Quatro estágios (imaturo, em desenvolvimento, maduro e desovado) foram determinados de acordo a estrutura e arranjo das células no ovário. Cada estágio corresponde, microscopicamente, a uma cor característica, exceto nos estágios I (imaturo) e IV (desovado) nos quais as cores são muito similares e podem ser distinguidas apenas histologicamente. A escala cromática varia do branco/translúcido (estágio I), cinza/verde (em desenvolvimento), verde escuro a preto (maduro). O tamanho médio das células foi 54,01 µm (±3,5) (estagio I), 136,80 µm (±8,8) (estágio II) e 199,80 µm (±6,4) (estágio III). A distribuição de frequência do tamanho das células foi polimodal, e diferentes estágios celulares foram observados nos ovários maduros, sugerindo a ocorrência de desovas múltiplas. A menor fêmea madura mediu 152 mm e o comprimento em que 100% das fêmeas estavam maduras foi 170 mm.

Reproductive cycle and size at first sexual maturity of the white shrimp Penaeus schmitti (Burkenroad, 1936) in northeastern Brazil

“…Our results also indicated that females present a significantly higher relative frequency in larger size classes, which have been previously reported for P. schmitti populations (Santos et al, 2005(Santos et al, , 2008. Penaeid females are larger than males due to the body space needed for gonadal development (Hartnoll, 1982;Dall et al, 1990) and thus more abundant in larger size classes (García & Le Reste, 1986) Studies of ovarian development in penaeids have been used as a tool for the establishment of guidelines for fishery management (Quintero & Gracia, 1998), as well as the improvement of breeding technology for aquaculture operations (Peixoto et al, 2003;Dumont et al, 2007;Gonçalves et al, 2009;Machado et al, 2009). Histological analyses of the ovaries are considered to be one of the most accurate procedures for the determination of the maturational stage of female crustaceans (Ohtomi et al, 2003;Carbonell et al, 2006).…”

“…Histological analyses of the ovaries are considered to be one of the most accurate procedures for the determination of the maturational stage of female crustaceans (Ohtomi et al, 2003;Carbonell et al, 2006). This approach may guarantee greater reliability for the determination of the maturation stage, given the precision in identification of the different developmental stages and the potential for comparisons with features observed macroscopically, such as the morphology and coloration of the gonad (Quintero & Garcia, 1998;Peixoto et al, 2003;Machado et al, 2009). The stages of ovarian maturation in penaeids have been defined according to the presence or absence of basophilic, vitellogenic, mature, and atretic oocytes (Quintero & Gracia, 1998;Peixoto et al, 2003;Dumont et al, 2007).…”

“…For the histological analysis, samples of the median portion of the ovary were collected from 20 specimens in different macroscopic maturation stages (Machado et al, 2009). The tissue was fixed in Davidson solution for 24 h and then transferred to 70% ethanol before being set in paraffin at 58ºC, sectioned (6 µm) and stained with Hematoxylin-Eosin (Bell & Lightner, 1988).…”

“…The oocytes were classified according to their histological characteristics, based on the descriptions proposed by Gonçalves et al (2009) and Machado et al (2009). The proportion of each type of oocyte was calculated for each month, and 30 oocytes representing each category (or the total number available, if less than 30) were measured using Image Tool 2.0 for Windows (The University of Texas Health Science Center in San Antonio, TX, USA).…”

“…However, the reproductive cycle of P. schmitti based on the relationship between macro and microscopic features during the ovarian maturation have been reported only to P. schmitti populations in southern Brazil (Gonçalves et al, 2009;Machado et al, 2009). Furthermore, data on reproductive dynamics, including gonadal development and size at first gonadal maturity are important parameters for the development of effective conservation strategies to monitor and control fishery activities in specific areas (Carbonell et al, 2006;Machado et al, 2009;Kevrekidis & Thessalou-Legaki, 2013).…”