Fernanda Menezes França

Physiological response of American bullfrog tadpoles to stressor conditions of capture and hypoxia

The American bullfrog (Rana catesbeiana), recently named Lithobates catesbeianus is currently farmed for commercial purposes throughout various regions of Brazil. Stressful situations such as problems of management, inadequate facilities and environmental changes with consequent reduction of immunity are common in intensive production. The assessments of these situations of stress allow us detect these problems decreasing the injuries causes by confinement. The main objective of this study was to use the biological markers of plasma cortisol and glucose level and hematological parameters to evaluate the response of bullfrog tadpoles submitted to stressed mechanisms of capture and hypoxia. The animals were subjected to three treatments: stress due to individual capture with a hand net; stress due to batch capture with a hand net; and stress due to capture by emptying. The results obtained demonstrated that there were no statistically significant differences in the parameters tested when comparing the treatments with and without exposure to air (normoxia and hypoxia). Based on these results we can conclude that the stressful stimuli tested were not adequate to alter the biomarker tested. For the cortisol, probably this should have occurred due to the synergistic action between this hormone and thyroxin, which induces metamorphosis in these animals.

Profile of cortisol, glycaemia, and blood parameters of American Bullfrog tadpoles Lithobates catesbeianus exposed to density and hypoxia stressors

The aim of this study was to evaluate alterations to the physiological profile (cortisol, glycaemia, and blood parameters) of Lithobates catesbeianus caused by the stressors density and hypoxia. The organisms were in the prometamorphosis stage and exposed to different tadpole densities: 1 tadpole/L (T1), 5 tadpoles/L (T2), and 10 tadpoles/L (T3) for 12 days. The blood was collected through the rupture of the caudal blood vessel and collected under normoxia (immediate collection) and hypoxia (after 15 minutes of air exposure) conditions. Cortisol levels rose on the fourth and eighth days of treatment and returned to basal levels by the end of the experiment. The stressor mechanisms tested did not affect glycaemia. White blood cells (total number of lymphocytes, neutrophils, and eosinophils) showed a significant difference at the twelfth day of the experiment when compared with the start of the experiment. We concluded that, under controlled conditions, a density of up to 10 tadpoles/L and air exposure for 15 minutes did not cause harmful physiological alterations during the experimental period. The answer to these stressors maybe was in another hormonal level (corticosterone).

Bisphenol risk in fish exposed to a contamination gradient: Triggering of spatial avoidance

Bisphenol A (BPA) is an emerging contaminant widely used in various industrial products. Sublethal toxicity of BPA on aquatic organisms is expected to occur at a concentration of around 500 μg L-1, which is much higher than environmentally realistic concentrations found in water bodies (up to 0.41 μg L-1). However, there is no information concerning how a BPA contamination gradient could affect the spatial displacement of organisms. We hypothesized that fish might be able to detect an environmentally realistic BPA contamination gradient and avoid potential toxic effects due to continuous exposure. Therefore, the objectives of this work were: (i) to determine if BPA could trigger an avoidance response in the freshwater fish Poecilia reticulata; (ii) to assess whether BPA-driven avoidance occurs at environmentally relevant concentrations; and (iii) to estimate the population immediate decline (PID) at the local scale, considering avoidance and mortality as endpoints. Avoidance experiments were performed in a seven-compartment non-forced exposure system, in which a BPA contamination gradient was simulated. The results indicated that BPA triggered avoidance in P. reticulata. In a traditional forced acute toxicity test, lethal effects in 50% of the population occurred at a BPA concentration of 1660 μg L-1, while in the non-forced system with a BPA concentration gradient, avoidance of 50% of the population occurred at a concentration four orders of magnitude lower (0.20 μg L-1). At environmentally relevant BPA concentrations, PID was mainly determined by the avoidance response. Avoidance in P. reticulata populations is expected to occur at BPA concentrations below those that cause sublethal effects on fish and are considered safe by international agencies (≤1 μg L-1). The approach used in the present study represents a valuable tool for use in environmental risk assessment strategies, providing a novel and ecologically relevant response that is complementary to traditional ecotoxicological tests.

Is hypoxia a stressor to American bullfrog tadpoles

The aim of this study was to evaluate alterations to the physiological profile of cortisol in pro-metamorphose phase tadpoles of Lithobates catesbeianus exposed to hypoxia stressor in a capture experiment and in a crowding experiment. The capture study was performed by the treatments: stress due to individual capture with a hand net, stress due to batch capture with a hand net and stress due to capture by emptying. Three simultaneous replicates was done witch 12 animals were sampled (6 normoxia - immediately blood collection) and 6 hypoxia - blood collection after 15 min of air exposition) in two collection times with 5 days by intervals. The crowding study was performed by the treatments 1 tadpole L-1, 5 tadpoles L-1 and 10 tadpoles L-1. Three simultaneous replicates was done witch 8 animals (4 normoxia and 4 hypoxia) were sampled in the zero moment (ZM) - blood collection before the experiment, 6 animals/treatment (3 normoxia and 3 hypoxia) to 4 and 8 days and 18 animals/treatment (9 normoxia and 9 hypoxia) to 12 days. The average values to plasmatic cortisol varying from 1.7 to 5.1ng mL-1 (capture study) and 1.0 to 4.2ng mL-1 (crowding study). It concludes that the biomarker tested (cortisol) showed no alterations front of the stressor used. Alternatively, a larger response pattern to these stimuli may have been expressed in another level of an unmeasured hormone (corticosterone). And the bullfrog has great ability to adapt to different management compared to other aquatic organisms, which demonstrates the plasticity of these animals.

Tracking viral particles in the intestinal contents of the American bullfrog, Lithobates catesbeianus, by Transmission Electron Microscopy

Feces are an important viral agent elimination route for infected carrier animals and in aquatic organisms these pathogenic agents can very rapidly propagate due to the habitation environment. The objective of this work is to track viral particles in the intestinal contents of bullfrogs (Lithobates catesbeianus) from five commercial frog farms in the region of Vale do Paraiba, in the State of Sao Paulo, Brazil, using negative contrast transmission electron microscopy (TEM). The Coronaviridae, Paramyxoviridae, Parvoviridae and Herpesviridae families were observed and photographed in specimens. This work emphasizes the importance of adopting sanitary measures in commercial farms and confirms that observing feces by TEM is an efficient and rapid diagnostic tool for detecting viral agents.