EGG QUALITY IN FISHES

Varying egg quality is one of the limiting factors for successful mass production of fish fry. It may also cause some of the variability in recruitment observed in many wild stocks, since poor egg quality may decrease the survival potential of the hatched larvae. In the literature, the term egg quality has been defined and used in various ways by different authors. Due to the limited knowledge in the field, it has been difficult to pinpoint valid quality criteria. The only definition of egg quality that has general validity is probably the egg's potential to produce viable fry. The egg's potential to produce viable fry is determined by several physical, genetic, and chemical parameters, as well as the initial physiological processes occurring in the egg. If one of the essential factors is lacking, or is incomplete, egg development will fail at some stage. Thus, egg quality should be regarded as determined when the egg has left the female fish and the fertilization process is complete. This definition is, however, of very little practical value, since fry viability obviously cannot be determined before the fry is produced. Good practical criteria for the determination of egg quality should be both possible to identify early in development, and be simple to use. The problems of egg quality have received increasing attention, in relation to cultivation as well as to the assessment of reproduction of wild fishes. This chapter discusses the possible criteria for the determination of quality of fish eggs. © 1990, Academic Press Inc.