Copper Resistance of Tilapia Larvae
In this study, they attempted to evaluate the effects of exogenous steroids on copper resistance and the relationship among steroids, Na+/K+-dependent adenosine triphosphatase (Na+-K+ ATPase), and ionic homeostasis after challenge with copper toxicity in tilapia larvae (Oreochromis mossambicus).
Tilapia larvae were reared on artificial feed containing 0 (control), 50 (low-dose), 125 (middle-dose), and 250 mg/kg (high-dose) cortisol or progesterone for 10 d before Cu2+ (1 mg/L) challenge for 72 h. The results indicated that both cortisol and progesterone significantly increased the activity of Na+-K+ ATPase, while progesterone was more effective than cortisol treatment at increasing the survival rates in larval fish after Cu2+ challenge. Upon larval exposure to waterborne Cu2+, the whole-body Na+ content was retained for a prolonged period. Larvae were treated with cortisol and progesterone to determine their effects on Cu2+ resistance and the resultant cation retention. Results for the effect of progesterone were clearer than those of cortisol. On the other hand, cortisol levels significantly increased after 10 d of exogenous administration of cortisol. While larval aldosterone levels increased, the cortisol content was not enhanced after 10 d of oral progesterone treatment. We suggest that in addition to progesterone, s involvement in copper resistance mechanisms in tilapia larvae by ion retention, aldosterone might also effectively enhance this mechanism.