Vitamin D synthesis in fish was studied using cholesterol and acetate as precursors. Crude liver homogenate preparation of Tilapia mossambica (Tilapia) incubated with 4-14C cholesterol was found not to result in the formation of radiolabelled vitamin D3. Intravenous injection of 4-14C cholesterol also did not result in the formation of 14C vitamin D3.
Intraperitoneal injection of 14C acetate was found not to have the label in vitamin D3 fraction of the whole fish. Thus, the results suggest the absence of a nonphotochemical pathway of vitamin D synthesis in fish or, even if it exists, cholesterol may not be the substrate. In addition, fish may not be able to synthesize secosteroid directly from 2-carbon units like acetate, to make vitamin D3.