Mônica Serra

The mobilization of an organism in response to noxious stimulation varies according to the degree of evolution of the nervous system, and the response, which is considered species-specific, depends on the type of noxious stimulus applied. Knowledge about the specific response of a species to a noxious stimulus is crucial to understanding the evolution of nocifensive responses and to providing information about the signals that can indicate discomfort or pain. The present study evaluated the behavioral and hormonal nociceptive responses of Oreochromis niloticus treated by subcutaneous injection of vehicle or formaldehyde 3% in the posterior region of the dorsal fin. Fish receiving formaldehyde injection spent less time with the soft ray dorsal fin moving and more time in a lowered position than vehicle-treated fish, and there was a negative correlation between these two variables in formaldehyde-treated fish. A skin-darkening pattern was identified in fish who died as a result of the noxious stimulus. The speed and distance traveled, plasma cortisol, body and eye darkening, and time spent with the spine ray dorsal fin erect were not significantly different between the treatments. The formaldehyde test activated the nociceptive system in O. niloticus and confirmed the hypothesis that the responses presented to this test are species-specific. In addition, the reduction of affected limb use (soft ray dorsal fin), similar to that observed in mammals submitted to the same test, indicates that pain sensation may be present in these animals. The mobilization of an organism in response to noxious stimulation varies according to the degree of evolution of the nervous system, and the response, which is considered species-specific, depends on the type of noxious stimulus applied. Knowledge about the specific response of a species to a noxious stimulus is crucial to understanding the evolution of nocifensive responses and to providing information about the signals that can indicate discomfort or pain. The present study evaluated the behavioral and hormonal nociceptive responses of Oreochromis niloticus treated by subcutaneous injection of vehicle or formaldehyde 3% in the posterior region of the dorsal fin. Fish receiving formaldehyde injection spent less time with the soft ray dorsal fin moving and more time in a lowered position than vehicle-treated fish, and there was a negative correlation between these two variables in formaldehyde-treated fish. A skin-darkening pattern was identified in fish who died as a result of the noxious stimulus. The speed and distance traveled, plasma cortisol, body and eye darkening, and time spent with the spine ray dorsal fin erect were not significantly different between the treatments. The formaldehyde test activated the nociceptive system in O. niloticus and confirmed the hypothesis that the responses presented to this test are species-specific. In addition, the reduction of affected limb use (soft ray dorsal fin), similar to that observed in mammals submitted to the same test, indicates that pain sensation may be present in these animals.

This study investigated whether fish ladder transposition is a stressful event for the streaked prochilod, Prochilodus lineatus, in a dam on the Upper Paraná River, Brazil. Bodyweight, standard length and plasma concentrations of cortisol, glucose, lactate, chloride and haematocrit were measured in 48 adult fish (male and female) that were sampled downstream and upstream of the dam and on the fish ladder. The results showed that the intense physical exertion of the fish during ladder transposition demanded high metabolic requirements and activated anaerobic pathways, but was not stressful. We recommend that physiological indicators should be used for post-construing assessments, which would improve the management of migratory fish species.

A manutenção de um bem-estar bom em animais mantidos em cativeiro e fazendas depende da avaliação apropriada do bem-estar destes animais, de modo a evitar manejo inapropriado e manter condições que provêm bem-estar bom. O uso de indicadores fisiológicos é encorajado, uma vez que estes são métodos quantitativos e não subjetivos. Entretanto, o uso de ferramentas fisiológicas é difícil para a avaliação de bem-estar bom. Quando são utilizadas como indicadores de estresse e dor, é preciso ter cautela na interpretação dos resultados bem como utilizar uma avaliação multicritério. Essa revisão sintetiza as premissas, as aplicações e a complexidade do uso de indicadores fisiológicos na avaliação do bem-estar animal.

Fluoxetine (FLX) is a selective serotonin (5-HT) reuptake inhibitor known for its effects modifying aggressiveness, personality traits, and anxiety-like behaviors. The aim of the present study was to evaluate the influence of the acute treatment, by immersion, with FLX on aggressive behavior of resident Brycon amazonicus fish. Fish pretreated with FLX presented an increase in aggressiveness, evidenced by the increase on the number of bites and chases against the intruder and a decrease in latency for the first attack, when compared to control fish. Together with previous studies, these results show the complexity of the neural modulation of the aggressive behavior in fish by 5-HTergic system.

The neural circuitry for social behavior and aggression appears to be evolutionarily conserved across the vertebrate subphylum and involves a complex neural network that includes the hypothalamus as a key structure. In the present study, we evaluated the changes in monoamine levels in the hypothalamus and on serum cortisol and plasma glucose of resident matrinxã (Brycon amazonicus) submitted to a social challenge (introduction of an intruder in their territory). The fight promoted a significant increase in hypothalamic 5-HT, NA and DA levels and on the metabolites 5-HIAA and DOPAC, and decreased 5-HIAA/5-HT and DOPAC/DA ratios in resident fish. Furthermore, an increase in serum cortisol and plasma glucose was also observed after the fight. Resident fish presented a high aggressiveness even with increased 5-HT levels in the hypothalamus. The alteration in hypothalamic monoaminergic activity of matrinxã suggests that this diencephalic region is involved in aggression and stress modulation in fish; however, it does not exclude the participation of other brain areas not tested here.

This study evaluated the influence of dietary L‐tryptophan (TRP) supplementation on the time course of aggressive behaviour and on neuroendocrine and hormonal indicators in juvenile matrinxã Brycon amazonicus. Supplementation with TRP promoted a change in the fight pattern at the beginning of an interaction with an intruder, resulting in decreased aggressive behaviours during the first 20 min. The decrease in aggression did not persist throughout the interaction but increased at 3 and 6 h after the beginning of the fight. Monoamine levels in the hypothalamus were not influenced by TRP before or after the fight; however, the hypothalamic serotonin (5‐HT) concentration and the 5‐hydroxyindole‐3‐acetic acid (5HIAA):5‐HT ratio were significantly correlated with the reduction in aggressive behaviour at the beginning of the fight. Cortisol was not altered by TRP before the fight. After the fight cortisol increased to higher levels in B. amazonicus fed with supplementary TRP. These results indicate that TRP supplementation alters the aggressive behaviour of B. amazonicus and that this effect is limited to the beginning of the fight, suggesting a transient effect of TRP on aggressive behaviour. This is the first study reporting the effects of TRP supplementation on the time course of aggressive interaction in fishes.

This study evaluated stress indicators of juvenile piau (Leporinus friderici) during and after a 4-hour transportation in order to establish an appropriate transportation protocol for this type of fish. Fish were transported in plastic bags (133.1 g/L) and sampled before loading, during 1, 2, 3 and 4 h and after transportation (2, 6, 12 and 24 h). Blood samples were analyzed for cortisol and glucose levels, hematocrit, hemoglobin level, number and mean corpuscular volume of erythrocytes. Water pH, dissolved oxygen, temperature and ammonia were monitored before, during and after transportation. No mortality was observed through the experiment. Ammonia levels increased throughout transportation, but the low pH values kept NH3 in safe levels for fish. Cortisol levels increased within 4 h of transportation, and returned to control condition 2 h after arrival. Plasma glucose increased within one hour of transportation, reaching peak value within 4 h and returning to initial condition 2 h after arrival. Erythrocyte number and hemoglobin levels showed the lowest levels 2 h after arrival, and mean corpuscular volume increased during transportation, decreasing at 12 and 24 h after arrival. Transporting piau is stressful, but fish recover the initial condition in short time, showing tolerance to the changes in the water quality parameters

This study evaluated the effect of dietary supplementation with l-tryptophan (L-TRP), a serotonin precursor, on the aggressiveness of juvenile matrinxã Brycon amazonicus. Fish were kept in individual aquaria for 7 days receiving the diets: D1 (control: 0.47% of TRP), D2 (0.94% of TRP), D3 (1.88% of TRP), and D4 (3.76% of TRP). After this, they were grouped with an intruder fish to establish a resident–intruder relationship during periods of 20 min. Blood cortisol, glucose, chloride, sodium and calcium; hemoglobin, hematocrit, red blood cell count and volume; liver glycogen and lipids were measured. Territoriality had significant effect on the aggressiveness of matrinxã (the residents were more aggressive than intruders, P < 0.001) and tryptophan significantly affected their behavior. Fish fed with the D2 diet presented a longer latency until the first attack (P = 0.0069) and bit the intruder fewer times (P = 0.0136) during the period of observation, compared to the control group. The frequency of bites and chases after the first attack was not affected by the dietary supplementation of TRP. Physiological variables were not significantly affected by the diet, except for a moderate increase in cortisol level in fish fed with D2 diet after the fight, indicating slight activation of the hypothalamus–pituitary–interrenal axis. The results show that juvenile matrinxã have aggressive and territorial behavior and that a diet containing 9.4 g TRP kg⁻¹ alter their aggressiveness, without affecting the stress-related physiological parameters.