## 3 Results and Discussion
### Danilo rerio
#### 3.1.3 Biochemical Markers  
After 96 h, FOS did not cause any significant variation in the glycogen content of zebrafish larvae (\(p>0.05\), Figure 3A); however, the proteins content increased at 2 and 20 mg/L FOS (\(p<0.05\), Figure 3B) and a decrease in lipids content was found at 2 mg/L FOS (\(p<0.05\), Figure 3C). Contaminants may change the total energy available on the organisms, which originates compensatory corrections in the energy metabolism to keep the homeostasis [46]. Lipids are considered the primary energy source mobilized when organisms are exposed to contaminants and, with the carbohydrates, they are rapidly mobilized to supply a sudden energy demand while proteins are the last choice of energy source, being usually mobilized only under severe conditions [46]. Decreased lipid contents may be a result of physiological stress response caused by FOS [47]. The detected effects on energy metabolism of zebrafish embryos after FOS exposure (increased protein content and decreased lipids' content) may compromise other biological functions, such as growth, reproduction, development, and locomotor activity. In our study, no effects were found on zebrafish development (e.g., in terms of hatching, heartbeat rate, and malformations' appearance) by 2 and 20 mg/L FOS. However, an increase in the distance swam by zebrafish larvae was found to 20 mg/L FOS, which may be related with the detected alterations on the energy metabolism.  
After 96 h, FOS induced no significant effects on ChE, CAT activities, and TG content of zebrafish larvae (\(p>0.05\), Figure 4A,C,D). However, FOS (2 mg/L) increased GST activity (\(p<0.05\), Figure 4B). Oxidative damage results from an imbalance between oxidants and antioxidant levels in the organism, which increases reactive oxygen species (ROS) generation. ROS may react with biomolecules, such as lipids and proteins, affecting cell viability [48; 49]. However, fish have effective antioxidant defenses comprised by various antioxidant enzymes (e.g., CAT and GST) and low-molecular-weight scavengers (e.g., glutathione (GSH)) [50; 51; 52]. GST is a phase II detoxification family of enzymes and an oxidative stress biomarker. The increased GST activity detected in zebrafish larvae after exposure to FOS may be associated to the elimination of lipid peroxides by GST-conjugated products [49]. GST may not be considered a highly sensitive biomarker regarding organophosphate exposures [17; 50; 51], but may be useful as a biomarker for long-term exposure scenarios, as it seems that it requires a longer exposure period to inhibit GST by organophosphates [18; 53; 54]. FOS did not also significantly alter the activity of CAT (another oxidative stress-related biomarker). Therefore, the lack of an effect on the tested enzymatic biomarkers could be due to the short time of exposure (96 h) [49]. However, a previous study reported a relevant increase of GSH after 1 h of exposure of zebrafish larvae to the pesticides diazmon and diuron [18]. Diazmon also caused an inhibition of ChE activity in zebrafish larvae [18]. Indeed, the primary target of organophosphates pesticides is the enzyme acetylcholinesterase challenge (AChE), which hydrolyzes the neurotransmitter acetylcholine in the peripheral and central nervous system [42]. Organophosphates are known to inhibit the activity of ChE [18; 55], whereas, in the current study, no effect was  
Figure 3: Effects of 96 h of exposure to fostyl-Al on zebrafish larvae for carbohydrates’ (**A**); proteins’ (**B**); and lipids’ (**C**) contents. Data are expressed as average value (AV) \(\pm\) standard error (SE). * Significant differences to control (\(p<0.05\)).  
detected in the ChE activity after the exposure to FOS, suggesting that FOS may have a distinct mode of action than the organophosphates pesticides. Moreover, the behavioral effects detected in the current study cannot be related to the alterations on ChE activity. A further neurotoxicity study with FOS should be provided to comprehend its role on the nervous system of non-target organisms.