Biologia reprodutiva da raia de água doce (Potamotrygonidae: Chondrichthyes) Plesiotrygon iwamae na baía de Marajó – Pará

Abstract

The family Potamotrygonidae is the only one among the elasmobranchs that has all its representatives exclusively in freshwater. Freshwater rays are being exploited for ornamental purposes and data on the biology of this group are rare. The objective of the present work is to study the reproductive biology of P. iwamae. Collections were made in the Bay of Marajó during the months of May/August/October/December 2000, on the islands of Colares and Cotijuba. A total of 36 specimens of P. iwamae were captured with spinnerets, 21 males and 15 females. The reproductive apparatus were fixed with 10% formalin, washed in water, preserved in 70% alcohol, and analyzed. The results obtained indicate that: P. iwamae uses as reproductive strategy viviparity with trophoderm matrotrophy; only the left ovary was shown to be functional, both uteri are functional and both testis as well; adult males present clasperes with an average length between 82 and 115mm, representing 19.5 to 22.7% of the disc width; ovarian and uterine fecundity averages were 3. 93 and 2.63 respectively; a maximum number of up to four embryos per female was observed and the calving season probably occurs at the beginning of the rainy season; disc width to first maturity was estimated at approximately 400mm for males and between 450 and 500mm for females. Low fecundity rate indicates that P. iwamae requires criteria for its sustained exploitation as an ornamental fish.