Sex ratio and sexual dimorphism of the anchovy Anchoa januaria (Actinopterygii, Engraulidae) in a tropical bay in south‐eastern Brazil

Abstract

Sex ratio and morphological traits of a very abundant anchovy Anchoa januaria were described in a tropical bay in south-eastern Brazil. The aim was to test the hypothesis that sexual dimorphism occurs due to the different reproductive roles of the sexes. A fish sampling programme was carried out between September 1998 and August 1999 at six sites: four sandy beaches and two lower-river sites. Population structure at river sites comprised adults only, ranging from 60 to 80 mm total length (L T ), while at sandy beaches both juveniles and adults were found, ranging from 32 to 80 mm L T . Well-balanced 'spawning school' at river sites during reproduction were detected, while female-dominated schools occurred in the bay feeding areas. Males had relatively longer pectoral fins, slightly larger hearts and more somatic mass than females. Females outnumbered males at sizes >67 mm L T and had significantly longer intestines and heavier livers than males. The largest size reached by females was probably related to a higher growth rate as they have a larger intestinal absorbing area for nutrients. The prediction of higher energetic investment in reproduction by females that should have larger organs associated with food acquisition and processing to produce energy-rich eggs was confirmed for A. januaria in Sepetiba Bay.

Reproductive dynamics of Lycengraulis grossidens (Clupeiformes: Engraulidae) and Platanichthys platana (Clupeiformes: Clupeidae) in a subtropical coastal lagoon

“…Because females invest more energy than males in reproduction, they tend to have a greater body weight and length (Jonsson and Jonsson, 2015). Size differences were also recorded for Anchoa januaria in Sepetiba Bay (southeastern Brazil), where females were larger than males (Santos et al, 2007). Larger females represent an advantage for the population, because they produce a larger quantity of high-quality gametes (Jonsson and Jonsson, 2015) that exhibit reduced vulnerability to predation (Helfman et al, 1987) and can better survive unfavorable periods (such as reduced food availability), due to the presence of larger energy stores.…”

Stratégie de reproduction du carangidae <i>Trachinotus teraia</i> cuvier, 1832 dans la lagune ebrié (Côte d’Ivoire)

“…Selon Aka et al (2004), la variation du sex-ratio dépend de l'état physiologique des poissons. En général, chez les téléostéens, les mâles sont prédominants en période de reproduction alors qu'en période de repos sexuel, ce sont les femelles qui sont prédominantes (Paugy, 1980 ;Santos et al, 2007). Plusieurs facteurs tels que le déplacement pour la recherche de nourriture, la croissance différentielle et le taux de mortalité par sexe influencent également le sex-ratio chez les poissons (Mellinger, 2002).…”

Habitat selection by anchovies (Clupeiformes: Engraulidae) in a tropical bay at Southeastern Brazil

“…Sergipense & Sazima (1995) also found A. januaria in higher abundance in sites in the inner zone between 1983 and 1985. Santos et al (2007) reported that A. januaria in Sepetiba Bay shows movements between feeding areas (sandy beaches in the inner Bay) and spawning areas (lower rivers reaches), another evidence that this species use low salinity waters in the bay.…”