Chronic exposure to sub-lethal concentration of a glyphosate-based herbicide alters hormone profiles and affects reproduction of female Jundiá (Rhamdia quelen).

This work was carried out to verify the effect of a glyphosate-based herbicide on Jundiá hormones (cortisol, 17ß-estradiol and testosterone), oocyte and swim-up fry production. Earthen ponds containing Jundiá females were contaminated with glyphosate (3.6mg/L); blood samples were collected from eight females from each treatment immediately before, or at 1, 10, 20, 30 and 40 days following contamination. A typical post-stress rise in cortisol levels was observed at the 20th and 40th days following exposure to glyphosate. At the 40th day, 17ß-estradiol was decreased in the exposed females. A similar number of oocytes were stripped out from females from both groups; however, a lower number of viable swim-up fry were obtained from the herbicide exposed females, which also had a higher liver-somatic index (LSI). The results indicate that the presence of glyphosate in water was deleterious to Rhamdia quelen reproduction, altering steroid profiles and egg viability.

Puberty influences stress reactivity in female catfish Rhamdia quelen.

We investigated a group of Rhamdia quelen females during their entire first reproductive cycle and beginning of the 2nd cycle by evaluating the stress response at different phases of gonadal maturation. In mammals, including humans, pubertal development modulates stress response reactivity due to the maturation of the neuroendocrine stress axis. These shifts in the stress reactivity were also detected in salmonid fishes. This effect comes from changes in the sensitivity of the stress axis glands or in the capacity of the adrenal tissue to synthesise glucocorticoids. Here, for the first time, we show that similar to mammals and salmonid fishes, pre-pubertal female R. quelen exhibit a protracted stress response compared to adult fish, pointing to puberty as a key event on HPI axis modulation.

Agrichemicals chronically inhibit the cortisol response to stress in fish.

We studied the stress response of Rhamdia quelen fingerlings at 45, 90, 135 and 180 d following acute exposure to agrichemicals. Herein, we report the novel observation that acute exposure of fingerling-aged fish to a methyl parathion-based insecticide (MPBI) and to a tebuconazole-based fungicide (TBF) induced chronic inhibition of the stress response. In contrast, fish exposed to an atrazine-simazine-based herbicide (ASBH) recovered the stress response on day 45, and fish exposed to a glyphosate-based herbicide (GBH) did not present stress response inhibition. Additionally, fish exposed to MPBI, GBH and ASBH showed lower survival rates and attained lower final weights. In the case of TBF, the presence of the stressful stimulus more strongly influenced the changes in the performance parameters than did the agrichemical exposure itself. An impairment of the cortisol response may seriously hamper the adaptive response and the ability to promote the necessary metabolic and ionic adjustments to respond to environmental stress.

Responsiveness of the interrenal tissue of Jundiá (Rhamdia quelen) to an in vivo ACTH test following acute exposure to sublethal concentrations of agrichemicals.

As in many aquatic environments, pollution is a widespread problem in Southern Brazil. In our previous work, we demonstrated that sublethal contamination with some agrichemicals impairs the capacity of fishes to elevate cortisol levels in response to an additional acute stressor. In earlier experiments, the experimental design did not allow us to conclude where this effect occurs. In the present work, we used the adrenocorticotropic hormone (ACTH) challenge test to help us identify if the impairment occur in the interrenal tissue. For this purpose, five experiments were conducted, each with one specific agrichemical (methyl-parathion, atrazine+simazine, atrazine, tebuconazole, and glyphosate) in sublethal concentrations of 16.6% of the LC(50-96h), as previously determined. Fish were subjected to the ACTH challenge test protocol as follows: group 1, were non-injected and maintained as the specific control group; group 2 received an injection of the vehicle alone (the saline group); and group 3 receive an injection of ACTH. One hour later, blood samples were taken from the caudal plexus, using sterile syringes. In all specific control groups, the injection of ACTH induced a strong rise in plasma cortisol, compared with the fish injected only with the vehicle and the non-injected group. Fish exposed to methyl-parathion and tebuconazole did not elevate cortisol in response to the ACTH injection, with values significantly lower than the control fish. Fish exposed to sublethal concentrations of atrazine+simazine, atrazine, and glyphosate showed a rise in plasma cortisol very similar to the control fish. We conclude that the ACTH challenge test revealed that R. quelen exposed to sublethal concentrations of tebuconazole and methyl-parathion had a reduced ability to elevate plasma cortisol in response to an intraperitoneal (i.p.) injection of exogenous ACTH, indicating that the interrenal tissue is the site of the impairment within the HPI axis. These ACTH challenge tests also revealed that the impairment of the cortisol response verified in fish exposed to atrazine+simazine and glyphosate, as shown in our previous work, seems to be related to steps of cortisol secretion in higher levels within the HPI axis.

Cortisol response to acute stress in jundiá Rhamdia quelen acutely exposed to sub-lethal concentrations of agrichemicals.

Exposure to agrichemicals can have deleterious effects on fish, such as disruption of the hypothalamus-pituitary-inter-renal axis (HPI) that could impair the ability of fish to respond to stressors. In this study, fingerlings of the teleost jundiá (Rhamdia quelen) were used to investigate the effects of the commonly used agrichemicals on the fish response to stress. Five common agrichemicals were tested: the fungicide - tebuconazole, the insecticide - methyl-parathion, and the herbicides - atrazine, atrazine+simazine, and glyphosate. Control fishes were not exposed to agrichemicals and standard stressors. In treatments 2-4, the fishes were exposed to sub-lethal concentrations (16.6%, 33.3%, and 50% of the LC(50)) of each agrichemical for 96 h, and at the end of this period, were subjected to an acute stress-handling stimulus by chasing them with a pen net. In treatments 5-7 (16.6%, 33.3%, and 50% of the LC(50)), the fishes were exposed to the same concentrations of the agrichemicals without stress stimulus. Treatment 8 consisted of jundiás not exposed to agrichemicals, but was subjected to an acute stress-handling stimulus. Jundiás exposed to methyl-parathion, atrazine+simazine, and glyphosate presented a decreased capacity in exhibiting an adequate response to cope with stress and in maintaining the homeostasis, with cortisol level lower than that in the control fish (P<0.01). In conclusion, the results of this study clearly demonstrate that the acute exposure to sub-lethal concentrations of methyl-parathion, atrazine+simazine, and glyphosate exert a deleterious effect on the cortisol response to an additional acute stressor in the jundiá fingerlings.

The color of illumination affects the stress response of jundiá (Rhamdia quelen, Quoy & Gaimard, Heptapteridae)

This paper provides the first data about physiological responses to stress in jundiá (Rhamdia quelen) exposed to different light colours. Jundiá is a species for fish production in the southern part of South America - and suitable for any region with a temperate or subtropical climates. In order to develop a light management for jundiá fingerlings during indoor maintenance and to understand the relationship between welfare and light colour in the jundiá, fingerlings were exposed to white, blue and green light. At the 10th day of light exposure an acute stressor was imposed. One hour after the application of the stressor, fish were sampled. Stress was assessed by means of cortisol determination. Our results show that green light seems to be the worst alternative to illuminate jundiá indoor experimentation facilities, or even fish transportation. The results also suggests that colour affects the stress response of jundia, and may be usefull for the management of this species.