Compositions and functions of the hatching froth from ricefield eel (Monopterus albus Zuiew).

The ricefield eel (Monopterus albus) is an economic fish species in China. To improve its artificial reproduction, we studied the compositions and functions of the hatching froth secreted by ricefield eels. The froth showed a viscosity of 2.72 mPaS, composed of glycoproteins with a sugar content of 0.156 mg/ml and a protein content of 0.250 mg/ml at a ratio of 1.60. The froth proteins were identified by SDS-PAGE as four proteins with the molecular weights of 42.5, 58.6, 65.3, and 98.2 kDa respectively. Their total amino acid content was 201.88 mg/100 ml, consisting of 16 kinds of amino acids. Filed observation revealed three beneficial effects of the froth on the hatching of the eel eggs. First, the froth increased the hatching rates of fertilized eggs at a range of water temperatures. Second, the froth decreased the rates of infection of the fertilized eggs by the water mold. Finally, the froth accelerated velum breakage in the fertilized eggs. Of the different hatching methods, froth incubation achieved the highest hatching rate and larvae survival rate. These results demonstrate the indispensable function of the froth of ricefield eels, and offer practical reasons for protecting the froth during the breeding season.