Oogenesis and in vitro reproduction of the twospot astyanax Astyanax bimaculatus (Linnaeus, 1758) exposed to conspecific alarm substance.

Stress situations can be essential to trigger reproduction in fish; however, it may also inhibit it. One of those situations involves the release of the conspecific alarm substance (CAS), a natural stressor, into the water by specific fish epidermal cells after a predator attack. Little is known about the effects of that substance on fish reproduction. This study aimed to evaluate the effects of CAS exposure on the oogenesis and reproduction of the twospot astyanax Astyanax bimaculatus before the hormonal induction for artificial reproduction. No macroscopic or cellular changes in the ovaries were observed for the females exposed to CAS, and the oocyte stages show all females in the same phase of maturation (Spawning Capable). Females exposed to CAS spawned 20 min before the females without exposure. On the other hand, they ovulated only once, whereas the females from the control group ovulated multiple times for approximately two hours after hormonal induction. Moreover, the precocious ovulation of the females submitted to CAS did not generate offspring, since all generated zygotes did not develop. In contrast, the control group females produced more than 11 thousand healthy larvae. Exposing the female fish to CAS during their reproductive management in captivity may reduce breeding success.

Seminal characterization of the Amazonian fire-eye tetra Moenkhausia oligolepis (Günther, 1864).

The seminal characteristics of Moenkhausia oligolepis are described. Three males were induced with a single dose of carp pituitary. Semen was collected 6 h after induction, and diluted in dibasic sodium phosphate extender solution. For motility analysis, 1 µl of diluted semen was added to 10 µl of distilled water to achieve gamete activation. The average duration of total motility was 76.67 s; while the average sperm motility rate at intervals of 15 s was 95.3, 85.3, 59.6, 31.7, 13.0, 4.6 and 1.2%. To determine sperm concentration in samples, 0.5 µl of semen was diluted with 500 µl of glutaraldehyde. An aliquot of 10 µl of this dilution was utilized for cell counting. An average count of 4.97 × 109 ± 3.46 sperm/ml was obtained. Morphological analyses were performed using eosin-nigrosine dye; 20.33% of the sperm were observed to be dead. Live sperm, comprising the other 79.67%, had an average length of approximately 30 µm, with a head diameter of 4.488 ± 0.7 µm; and a flagella plus mid-piece length of 26.071 ± 12.4 µm. Of those sperm, 69% had a normal morphology, while 31% had primary and secondary abnormalities. The observed abnormality rate did not have a detrimental effect on artificial fertilization potential for the species. The description of the seminal characteristics of a species is one of the most important sets of information required for artificial reproduction of fish in captivity. It also contributes significantly to the total biological knowledge of the studied species.

A model to study orienting responses in zebrafish, and applications towards the emotion-cognition interaction.

Orienting responses (ORs) are whole-organism reflexes that are elicited by innocuous stimuli, and which decrease in magnitude after stimulus repetition. ORs represent relatively simple responses that can be used to study attentional processes, and are modulated by the organism's state, including arousal and activation levels, as well as by emotional processes. Here we describe a simple method to study ORs in zebrafish, a model organism increasingly being used in behavioural neuroscience. After presentation of a static visual stimulus, an OR is elicited, characterized by approaching the stimulus and orienting towards it. After repeated stimulation, OR decreases, suggesting habituation. These responses are qualitatively altered by exposure to a fear-eliciting alarm substance (i.e., derived from the skin of a conspecific), since exposed animals avoid the visual stimulus and orient either away from the stimulus or towards it, but at a distance. The protocol can be used to study orienting responses, as well as the impact of fear and arousal on these reflexes.