Responses of the ultimobranchial gland to vitamin D3 treatment in freshwater mud eel, Amphipnous cuchia, kept in different calcium environments.

Freshwater mud eel, Amphipnous cuchia, were injected intraperitoneally daily with 100 ng of vitamin D3/100 g body weight and maintained in media containing either no calcium or different calcium concentrations. The eels were killed after 1, 3, 5, 10 and 15 days following the treatment and their serum calcium levels were measured. The ultimobranchial glands were fixed and processed using the routine paraffin method for histological studies. The results of the present study indicate that vitamin D3 can induce hypercalcaemia in eels kept in different calcium environments. Also, the ultimobranchial glands became hyperactive following vitamin D3 treatment. It is concluded that in mud eels, the gland has a calcium-regulating function.

Vitamin D3-induced calcemic and phosphatemic responses in the freshwater mud eel Amphipnous cuchia maintained in different calcium environments.

Vitamin D3 (100 ng 100 g body weight-1 day-1) was administered intraperitoneally (i.p.) to the freshwater mud eel Amphipnous cuchia kept in artificial freshwater, calcium-free freshwater, low-calcium freshwater (0.2 mmol/l CaCl2) or calcium-rich freshwater (13.4 mmol/l CaCl2) for 15 days. Analyses of serum calcium and phosphate levels were performed on days 1, 3, 5, 10 and 15 after the beginning of the experiment (six eels from each group at each interval). Administration of vitamin D3 elevated the serum calcium [maximum elevation occurred at day 10 in artificial freshwater (vehicle: 10.55 +/- 0.298, vitamin D: 13.90 +/- 0.324), low-calcium freshwater (vehicle: 11.17 +/- 0.220, vitamin D: 12.98 +/- 0.297) and calcium-rich freshwater (vehicle: 11.24 +/- 0.373, vitamin D: 14.24 +/- 0.208) whereas it occurred at day 5 (vehicle: 8.42 +/- 0.253, vitamin D: 11.07 +/- 0.328) in calcium-free freshwater] and phosphate levels [maximum elevation at day 15 in artificial freshwater (vehicle: 4.39 +/- 0.105, vitamin D: 5.37 +/- 0.121), calcium-free freshwater (vehicle: 4.25 +/- 0.193, vitamin D: 5.12 +/- 0.181), low-calcium freshwater (vehicle: 3.93 +/- 0.199, vitamin D: 5.28 +/- 0.164) and calcium-rich freshwater (vehicle: 3.77 +/- 0.125, vitamin D: 5.46 +/- 0.151)] of the fish maintained in the above mentioned environmental media, but the responses were more pronounced in the fish kept in calcium-rich media.