The reproductive biology and cycle of &lt;em&gt;Rioraja agassizi&lt;/em&gt; (Müller and Henle, 1841) (Chondrichthyes: Rajidae) in southeastern Brazil, SW Atlantic Ocean

María Cristina Oddone,Walter Norbis,Patricia L Mancini,Alberto F Amorim,Gonzalo Velasco

doi:10.3989/scimar.2007.71n3593

Abstract

Specimens of Rioraja agassizi were collected at Guaruja pier, Sao Paulo State, Brazil, from March 2005 to March 2006. A total of 275 males were captured. Based on the analysis of the clasper length, gonad weight, clasper gland length, alar thorns and lobule diameter, the size-at-maturity was estimated to be 32 cm. There were 1049 females in the record. Size-at-maturity was calculated in 40 cm. Sexual resting females were observed. Gonadosomatic and hepatosomatic indexes varied significantly in both sexes throughout the year. However, ovulation, egg-laying and presence of sperm in the seminal vesicle were observed all year round. For this reason, an annual cycle with at least one peak in the sexual activity is proposed for this species.

Highlights

Elasmobranchs (Chondrichthyes) have an evolutionary history of more than 400 million years, sufficient time for them to develop exquisite senses and complex reproductive modes that rival those of the most advanced tetrapods
The aims of this work were to describe the sexual development of males and females of R. agassizi, to estimate its size-at-maturity and to analyse the trend of the reproductive variables for this species on an annual basis in southeastern Brazil
All individuals with total length (TL) of up to 32 cm had uncalcified claspers, but from this size onward specimens with calcified claspers began to alternate with those with uncalcified ones

Summary

Introduction

Elasmobranchs (Chondrichthyes) have an evolutionary history of more than 400 million years, sufficient time for them to develop exquisite senses and complex reproductive modes that rival those of the most advanced tetrapods. The probable ancestral condition in elasmobranchs (Carrier et al, 2004), foreshadows the situation common in reptiles and universal in birds (Callard et al, 1988). The family Rajidae is oviparous and lays its egg capsules in the environment, where they develop. Oviparity in skates is single (external) (Musick and Ellis, 2005) and all Rajids have the same general reproductive cycle, in which egg capsules are deposited in pairs with intervals of 0-5 days between successive depositions (Holden et al, 1971). There is a peak in egg laying during the summer and spawning occurs throughout the entire year (Clark, 1922)

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