Atrazine and its degradates have little effect on the corticosteroid stress response in the zebrafish.

The present study examined the effects of atrazine on basal and forced swimming induced changes in whole body cortisol content in adult zebrafish. Zebrafish were exposed to graded concentrations of atrazine or the atrazine degradates deisopropylatrazine (DIA), deethylatrazine (DEA) and diamino-s-chlorotriazine (DACT) for up to 10 days. Some fish were sampled for the measurement of whole body cortisol levels under basal conditions while others were sampled after being subjected to a 20 min swimming challenge in order to quantify stress induced cortisol levels. In one experiment, zebrafish were subjected to two bouts of forced swimming 3h apart to test whether prior atrazine exposure affects the ability of the fish to respond appropriately to a repeated stressor. The results demonstrated that controls not exposed to atrazine and zebrafish exposed to atrazine or the atrazine degradates at nominal concentrations of up to 100 µg/L consistently exhibited increased whole body cortisol content in response to the swimming challenge. Separate analyses revealed few changes in basal or stress induced cortisol levels following atrazine exposure. Overall, these data suggest that atrazine and some of its degradates at the concentrations tested have minimal effects on the cortisol mediated stress response in the zebrafish.

Survival and iono-regulatory performance in Atlantic salmon smolts is not affected by atrazine exposure.

This study was conducted to determine the potential effects of atrazine exposure on survival and physiological performance in Atlantic salmon (Salmo salar) during the period of smoltification. This study involved two separate experiments in which juvenile Atlantic salmon were exposed to atrazine for a four day period in freshwater after which the fish were transferred to 50% seawater for two days and then to 100% seawater for five more days. The nominal concentrations of atrazine tested (1, 10 and 100 microg/L) were representative of and exceeded the levels measured in the North American freshwater environment. After seven days in seawater, fish were weighed, bled for the determination of plasma electrolyte levels, euthanized and samples collected for the determination of gonadosomatic index, muscle water content and gill Na+/K+-ATPase activity. Measured atrazine concentrations during the freshwater exposure period were 76-99% of nominal levels. There were no mortalities attributed to atrazine exposure. There were also no statistically significant differences in body weight, plasma sodium, potassium, magnesium and chloride levels, muscle water content or gill Na+/K+-ATPase activity between control and atrazine treated fish. Measurement of testis and ovary weights showed that there were no treatment effects on relative gonad size in male or female fish. These studies have shown that short term exposure to atrazine during the freshwater phase of their lifecycle had no effects on subsequent survival, body weight, relative gonad size or various measures of iono-regulatory performance in juvenile Atlantic salmon upon transfer to seawater. The concentrations of atrazine tested exceed those likely to be experienced in the natural aquatic environment suggesting that short term exposure to atrazine does not pose a risk to Atlantic salmon during the period of smoltification.

Retinoid requirements in the reproduction of zebrafish.

This study examines whether retinoids are essential in the reproduction of zebrafish. Using RT-PCR, it was shown that the ovaries and testes express enzymes that synthesize and metabolize the hormone retinoic acid (RA) (raldh2 and cyp26a, respectively), and RA receptors (raraa, rarga, rxrba, rxrbb, rxrga but not rxrab). Three new isoforms of rxrba were also observed in a variety of tissues. In other experiments, zebrafish were exposed for 11 d to diethylaminobenzaldehyde (DEAB), an inhibitor of RA synthesis, or fed a retinoid deficient diet for 130 d in order to evaluate the functional requirements of retinoids in reproduction. DEAB altered cyp26a transcript numbers in the gonads, suggesting an impact on RA, and decreased the number of spawned eggs by 95%. The retinoid deficient diet decreased whole body retinoids (retinol and retinal) by 68% in females and 33% in males. Females fed the retinoid deficient diet also produced 73% fewer eggs that contained 78% less retinal than controls. Fertilization rates were not affected. These studies have shown that the RA receptors are expressed in zebrafish gonads, and RA is required for the spawning of eggs. Dietary retinoid content influences reproduction, while retinyl ester storage levels appear to be of little significance. Females were more susceptible to retinoid perturbation than males, likely due to the cost of retinal deposition in the eggs. Overall, these studies have shown retinoids play a fundamental role in the reproduction of zebrafish, and the lack of retinyl ester stores in controls that successfully spawned illustrates that we have only a limited understanding of the retinoid physiology and requirements of fish.