Page 232 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

230 MARINE FISH: BREEDING

Reproduction and breeding

The breeding habits of tropical marine fish are not well documented
because only a small number of species have reproduced in captivity.
A few groups, however, such as clownfish, gobies, and sea horses,
breed with relative ease. Others, such as angelfish, may spawn
in aquariums, but their young are so poorly developed when
they hatch that it is extremely difficult to raise them successfully.

Ensuring that you have at least one mixed-sex pair from which
you can breed is problematic with marine fish, since in most
species the males and females are visually alike. However, if
the fish can be kept in a group, their behavior should give
you some clues to the sex of the fish. Two similar-looking
fish that fight are probably males involved in a territorial
dispute. Conversely, two fish that get on amicably may well be
a compatible male and female. Unusual swimming motions More than 15 different species of clownfish have now been bred in
aquariums. If you do not want to wait for young clownfish to grow to
or postures could be signs of courtship, which will indicate sexual maturity, you can buy a pair of adults from an aquarium store.
that you have a pair in the tank. Slight physical differences
sometimes become apparent toward spawning time, when Some species can change sex, which actually helps rather
females develop a noticeably plumper belly as they swell than hinders the process of finding breeding pairs. All young
with eggs. In addition, the males’ color often intensifies clownfish (see pp.244–245), for example, are male, but if you
and their patterning becomes better defined at this time. have a small group—even just two—the dominant fish will
change into a female and pair up with the next dominant
male. The sex change goes the other way in hawkfish (see
p.278) and some angelfish (see pp.252–255), with the dominant
CONDITIONING IN AQUARIUMS
individual in an all-female group turning into a male.
The factors that trigger spawning in the wild are largely unknown, Regardless of the species, you will need to be patient if
so there is little you can do to encourage marine fish to breed except you want to breed from fish you acquire as juveniles. The onset
to ensure that conditions in their tank are as close as possible to of sexual maturity is generally determined by size, rather than
those in their natural habitat. This means that the water must be at
the correct temperature and salinity, and also of good quality, so by age. It can take three months for young gobies (see pp.260–
efficient filtration and regular partial water changes are essential. 261) to reach breeding size, and with clownfish, you may be
Make sure that the fish get enough light—typically about 14 hours waiting for up to a year before they are sexually mature.
per day. The breeding stock should be mature, healthy, and well fed
on a protein-rich diet. If they Keen observation is needed to Spawning at sea
need rocks, shells, or caves for tell whether fish like these gobies
spawning sites, be sure that these have spawned, because they hide Marine fish have spawning habits broadly similar to those of
are included in their tank. their eggs in shells or small caves. freshwater species (see pp.64–66). Some marine fish form
long-term or temporary pairs; others spawn in small groups or
even in mass gatherings. Fertilization is usually external. Most
tropical reef fish, such as angelfish and butterflyfish (see pp.256–
259), are egg-scatterers, releasing floating eggs into the open
ocean to rise to the surface and be swept along with the
current. The fry are not fully developed when they hatch,
which is why they are often called larvae. Lacking fins, they
cannot swim and simply drift in the surface waters, feeding on
microscopic plant and animal life called plankton. Only when
they are larger and fully formed do they swim back to the reef.

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