Changes with time of ammonia and urea concentrations in the blood and tissue of mudskipper fish, Periophthalmus cantonensis and Boleophthalmus pectinirostris kept in water and on land

Abstract

1. 1. Changes with time of ammonia and urea concentrations and the ratios of urea-N:ammonia-N in the blood, liver, muscle, skin and gills of P. cantonensis and B. pectinirostris were studied in order to clarify whether or not conversion from ammonia to urea is performed in the fish during the period out of water. 2. 2. In P. cantonensis, ammonia concentration in all the samples except for the liver was ordinarily higher in the fish out of water than in the fish in water. But urea concentration in all the samples was higher in the fish in water than in the fish out of water and decreased in the fish both in and out of water as the breeding period became longer. On the other hand, the ratio of urea-N:ammonia-N also showed a similar trend to urea. 3. 3. In B. pectinirostris, both ammonia and urea concentrations in all the samples were ordinarily higher in the fish out of water than in the fish in water. But, the relative size of the ratio of urea-N:ammonia-N between the fish in water and the fish out of water differed according to the kind of samples and the length of breeding period. Moreover, the ratio in the fish out of water decreased suddenly in all the samples after day 3 when ammonia concentration in the fish out of water increased suddenly. 4. 4. The above results suggested that conversion from ammonia to urea during the period out of water is not performed by P. cantonensis and B. pectinirostris.