Spawning Methods

Sexually, fish can be classified into two groups: the sexually dimorphic and the sexually
isomorphic species. The sexually dimorphic species show obvious primary and secondary
characteristics of their gender. The males of this species are often larger and more
colorful, and they usually have a much more elaborate finage. The sexually isomorphic
species show hardly any apparent differences in the two sexes. It is therefore very
difficult to distinguish between the two sexes in this group. Often, the only deciding
factor could be the shape of the genital papilla. This becomes visible at the time of
spawning. In some of these species, the female have a more rounded belly or is slightly
larger than the males. There are some species that show no visible difference at all
between the two sexes.
External fertilization followed by egg laying is the way most fish in aquariums will
reproduce. Egg layers are classified into five groups: