One of the more rewarding aspects of fishkeeping is seeing your fish multiply in numbers. Most fishkeepers see this as justification in their methods of fishkeeping, although we all know that many of our fish breed despite of our treatment of them, such is the urge to maintain the species.

METHODS OF REPRODUCTION: All fish breed from eggs, but it is the
                                                    development of the fertilised eggs that gives
                                                    us the diversity in reproduction methods.

The majority of fish are egg-layers where the fertilised egg develops outside of the fish's body. The unfertilised eggs are first expelled from the female under stimulus from the attention of the male.

Eggs may be simply released amongst plants or scattered in open water to be fertilised by the free-swimming male;
they may be deliberately laid on a pre-selected spawning site
or placed in a floating bubblenest;
they can be laid out of water on an overhanging terrestrial plant leaf (or on the tank's cover glass);
they can be buried in the substrate;
they can be incubated in the parent's mouth.

Several of these methods have evolved to give better protection for the development of the egg and subsequent fry.

Alternatively, with the livebearing fishes, the fertilised eggs remain in the female's body to develop and later emerge as free-swimming fry.
A variation in this method allows females to store sperm from the male so that further batches of young can be produced without any further 'mating' being required. An even more sophistication allows developing fry to obtain nutrients from the female via a primitive 'placenta'.

Such are the diverse methods awaiting fishkeepers wanting to breed their fish.

SEXING : The first practical barrier to overcome is sexing the fish and making
                 sure you have a male and a female to breed with.

Livebearing species are easy to sex: the male has the anal fin transformed into a rodlike structure, the gonopodium, through which he injects sperm into the female. Females have the traditional fan-shaped anal fin.

It is important to strictly control which fish breeds with which: livebearers are notoriously promiscuous and will interbreed indiscriminately.
Only put together fish of the same strain unless you really want a thankful of 'mongrels' as a result!

Egglaying species need to be observed a bit more carefully.

Males are generally more colourful and have longer finnage.
Females usually are plumper in the body
(due to the build up of eggs) when viewed
from above.

Egglayers generally breed true without too many surprise packages amongst the offspring.

Sexing Goldfish:

When in breeding condition, males develop
small white breeding 'tubercles' on the
gill-covers and on the first thick rays of
the pectoral fins (see ringed areas, left).

© FBAS 1998 RCM/RDE             Aquarium Management Care Sheet 7 1/2

next page

                                    Download this complete Care Sheet