Epler, P. and Kamler, E. and Bieniarz, K. (1981) Investigations on artificial maturation of females of European ell (Anguilla anguilla L.): quality of eggs. Pol. Arch. Hydrobiol., pp. 135-146
| Species | Development state | Trait | Primary Data | Secondary Data |
| Anguilla anguilla | Egg | Oocyte diameter | Eggs of 1.0-1.3 mm in diameter have been considered to be fully ripened | 1.15 mm |
| Anguilla anguilla | Female | Maximum GSI value | GSI equalled from 35.1 to 42.3 | 35.1 percent |