Patterns of oocyte development in natural habitat and captive Salminus hilarii Valenciennes, 1850 (Teleostei: Characidae)

Abstract

Fecundity and oocyte development in Salminus hilarii female brood stock were analyzed with the aim of investigating the impact of migration impediment on oogenesis. Histological analyses of the ovaries were performed in adult females caught in two different environments--the Tietê River (natural) and captivity--and the gonadossomatic index, oocyte diameter and fecundity determined. Five germ cell development stages (oogonium, perinucleolar, cortical alveoli, vitellogenic, ripe) and two other structures (postovulatory follicles and atretic oocytes) were observed in females caught in the river. Captive animals lacked the ripe oocytes and postovulatory follicles and had a relatively higher number of atretic oocytes. Females in captivity are known to produce larger oocytes, and they release fewer eggs in each spawn (absolute fecundity) when compared with animals that are able to migrate. Our results suggest that the Tietê River is undergoing alterations which are being reflected in the reproductive performance of S. hilarii, mainly due to the presence of atretic oocytes in females caught in the river. The lack of postovulatory follicles and ripe oocytes in captive animals reveals that migratory impediment negatively impacts final oocyte maturation. However, the stage of maturation reached is adequate for ovulation induction with hormone manipulation.

Influence of spawning procedure on gametes fertilization success in Salminus hilarii Valenciennes, 1850 (Teleostei: Characidae): Implications for the conservation of this species

“…Histological analysis showed that the stage of maturation reached is adequate for induced ovulation, due to the presence of several vitellogenic oocytes and post-ovulatory follicles after induction. However, some oocytes were not released and became atretic (Dias et al, 1998(Dias et al, , 2005Honji et al, 2006Honji et al, , 2009. This phase of the development is observed and discussed in some works, including studies in S. hilarii (Takahashi, 2006;Honji et al, 2009).…”

“…The general morphology of eggs and larvae from G1 and G2 did not differ during development. Therefore, this analysis was performed only to confirm the stage of development because details of this development have already been described by Honji et al (2009).…”

“…The broodstocks (100% survival) were maintained in two ponds (300 m 2 each) and fed with commercial extruded feed for carnivorous (40% crude protein, Purina ® TC40). Sampling methods are according to Honji et al (2009).…”

“…After assessing the maturation stages of the gonads each month (described by Honji et al, 2009), the first artificial breeding of the wild males and females in captivity was scheduled for December 2005 using a carp pituitary treatment. The gamete release occurred naturally (without stripping the broodstock) and the fingerlings produced (first-generation offspring, F1) were stocked in the fish farm ponds for future broodstock captive rearing.…”

“…Several oocytes were collected to better examine their size, appearance, and diameter homogeneity, which are important criteria used to establish the spawning readiness of a total spawning species such as S. hilarii (Harvey & Carolsfeld, 1993;Honji et al, 2009). The homogeneity of oocytes' diameters was analyzed under a stereomicroscope (Zeiss, Stemi -SV6) with an ocular micrometer (Coleman), taking into account the data shown by Honji et al (2009). Running sperm was detected in males using a soft abdominal massage, and these individuals were selected.…”