During the Spring 2001 a survey was carried out in the Central Mediterranean Sea to estimate total commercial catches, discarded catches and the biodiversity indices of fishes (bony fish, elasmobranches). The study area is a very important fishing ground of the Central Mediterranean Sea. This area was divided into 7 sub areas. Discard and commercial catch samples were collected by 14 sample boats (two samples for each area). The commercial abundance index for Merluccius merluccius, Mullus barbatus, Mullus surmuletus, and Pagellus erythrinus was 1.865 g/h, 356 g/h, 649 g/h and 458 g/h, respectively. The bony fish represent tha main component of the total discard catch with mean value (in all area) was 1643 n/h and 28759 g/h. The results showed that Merluccius merluccius is the most important component of the total commercial catch, representing 58.5% of the target commercial bony fish species. The most common measures of biodiversity were used: Richness (S), Simpson's index (D), Shannon-Wiener's index (H). The values of the biodiversity indices per bony fish and elasmobranches in the Central Mediterranean Sea were: S=82; D=0, 19; H= 2,49 and S= 13; D=0,25; H= 1,7 1; respectively. The differences in catch between bony fish and elasmobranches is due, probably, to the fishing effects on demersal fish communities through selective removal of target species.