Reproductive aspects of the Jenynsia multidentata.
In the shallow estuarine zones of Patos Lagoon, this small fish (< 9 cm of total length) represents an important component of the fish assemblage (Chao et al. 1985). Several features such as its high abundance and occurrence year-round in the estuary, its great resistance to salinity and temperature variations, and the fact that is easy to catch and to maintain in aquarium, make this species a suitable model for laboratorial studies (Mai et al. 2005).
Although studies about reproduction and life history strategies of J. multidentata in the Patos Lagoon estuary have been already carried out (Betito 1984), there is little published articles concerning its biology in this system (Garcia et al. 2004, Mai et al. 2005). For instance, Garcia et al. (2004), based exclusively on recruitment patterns (abundance per size class plots), suggested that J. multidentata has an annual reproductive cycle in Patos Lagoon estuary that is composed by two cohorts: one comprised of individuals born from December to March that started reproducing during late winter and spring, and a second cohort comprised of individuals born from September to November that started reproducing during late summer and fall. However, there is no current published information regarding the reproductive biology of J. multidentata in this estuary that has been based on direct evidences obtained by dissection and analysis of the individuals. Moreover, there is still certain debate about which factors drive the markedly sexual dimorphism in size (females being larger than males), the larger number of females in relation to
the males and the amplitude of reproductive season for this species (Bisazza et al. 2000, Garcia et al.
knowledge about the biology of J. multidentata in Patos Lagoon estuary, the present work examine some reproductive aspects of this species, such as the reproductive season, period of gonad maturation and sexual ratio and their correlations with abiotic factors (salinity, temperature e water transparency).
Materials and methods
Sampling was conducted in the estuarine zone of Patos Lagoon, Rio Grande, RS, Brazil. The specimens analyzed where caught in three location within the shallow bays (< 2m) of the estuary: Saco da Mangueira (32°05’S; 52°07’W), Marambaia (31°59’S; 52°05’W) and Prainha (32º 09’S; 52º 06’W) (Fig. 1). The sampling was part of a larger long-term ecological project called ‘Pesquisas Ecológicas de Longa Duração (PELD)’, which have been carrying out monthly fish sampling in several locations within the estuary since 1999. From March 2000 to February 2001, the specimens were collected each month using a beach seine net (locally known as ‘picaré’) with the following dimensions: 9 × 1.5m net with 13mm bar mesh in the wings and 5mm in the center 3-m section. The samples were preserved in formalin 10% after caught and then were, kept in alcohol 70%, then stored at the FURG Fish Collection (http://www.ictio.furg.br/).
Figure 1. Map of Patos Lagoon estuary and Rio Grande City (32°S). Black dots denotes the sampling locations: (1) Saco da Mangueira; (2) Marambaia; and (3) Prainha.
Pan-American Journal of Aquatic Sciences (2007), 2 (1): 40-46