Recent advances in ovulation synchronization and superovulation in ...

Abstracts. II International Symposium on Animal Biology of Reproduction, Nov. 19-22, 2008, São Paulo, SP, Brazil.
The ovarian morphology and follicular maturation of an Amazonian fish Agoniates
halecinus (Müler & Toschel, 1845)
R.N. Santos 1 , S. Amadio 1
1 National Institute for Amazonian Research.
Introduction
Agoniates halecinus (Müler & Toschel, 1845), a medium sized freshwater characid known as “sardinha dentuda”,
can reach up to 20 cm of standard length (1). It is a common species of the Amazon basin, inhabiting mainly river
banks and lakes. Despite of no commercial value this species plays an important ecological role as a piscivore (2)
and it has a regulating function on the fish assemblage where it occurs. Here we present original results on the
ovarian morphology and follicular development of A. alecinus from Balbina’s reservoir, the largest flooded area due
to damming in Central Amazonia.
Materials and Methods
A total of 42 females ranging from 105 to 230 mm in standard length and 53.3 to 293 g in total weight were caught
at Balbina’s reservoir, in the State of Amazonas, Brazil. The preserved ovaries were embedded in paraffin, sectioned
at a 5-7 μ thickness, and stained with Harris Hematoxylin and Eosin (H&E). At least two slides were prepared for
each ovary. The description of each oocyte development phase was made according to terminology proposed by
teleostenas fishes (3).
Results and Discussion
Along the reproductive cycle, during the different maturation stages, fish ovary changes in size and color. Ovarian
histological sections of A. halecinus revealed there are no veins and medullar zones as it is expected for most
teleosteans (4). The inner wall presents a conjunctive tissue capsule, also called the ovarian tunic, formed by smooth
muscle fibers and blood vessels. The first growth phase of the oocyte development is represented by the oogonia,
which are the smallest oval cells of the germinative lineages. In the second growth phase, the chromatin nucleolus
oocytes are present, and are originated from the oogonia. During the following phases, a large and voluminous
nucleus, and several small rounded nucleoli adhering to a small membrane called the cariotheca, can be seen. As
maturation advances, a process of vitellogenesis occurs, when the oocytes show extra-vesicular yolk deposition. In
the vitellogenic (mature) oocytes, the largest ovarian cells, protein yolk granules (protein vitellus) and cortical
vesicles (lipid vitellus) are present. After maturity, follicles break down to allow oocyte release and post-ovulatory
follicle formation follows. In the A. halecinus ovary, it was possible to observe the presence of atresic follicles,
which shows an irregular shape, intense cell disorder with wrinkled follicles, and follicular cell invasions (process of
phagocytosis). This degenerative phenomenon can happen in any phase of fish reproductive cycle, however it is
more frequent during the late maturity phases or in oocytes not eliminated after spawning. Atresia when occurring in
ripe females or mature oocytes is associated to decreasing reproductive potential of a species.
References
(1) Lima FCT, Zanata A. 2003. Subfamily Agoniatinae. In: Reis RE, Kullander SO, Ferraris Jr CJ (Eds.). Check list
of the freshwater fishes of South and Central America. Porto Alegre: CLOFFSCA, EDIPUCRS. pp.291-309; (2)
Silva CC. 2006. Dieta da comunidade de peixes na área de influência da UHE de Balbina - Rio Uatumã, Amazonas,
Brasil. Dissertação de Mestrado. Instituto Nacioal de Pesquisas da Amazônia. 64pp; (3) Santos RN, Andrade CC,
Santos AFGN, Santos LN, Araújo FG. 2005. Hystological analysis of ovarian development of the Characiform
Oligosarcus hepsetus (Cuvier, 1829) in a Brazilian reservoir. Braz J Biol, 65:169-177; (4) Vazzoler AEAM. 1996.
Biologia e reprodução de peixes teleósteos: teoria e prática. Maringá: EDUEM, São Paulo: SBI. 169pp.
E-mail: santosrn@gmail.com
Anim. Reprod., v.6, n.1, p.213, Jan./Mar. 2009 213