Page 329 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

REPRODUCTIVE CYCLE 327

in Red Shiners they run along the top of the head. In some
groups, such as sticklebacks, the males become more brightly
colored to attract mates and deter rivals. In all coldwater GOLDFISH EGGS AND FRY
species, the females become fatter-bodied than their male The incubation period of goldfish eggs and the growth rate of the fry
counterparts as they swell with eggs prior to spawning. are both temperature-dependent: generally, the warmer the water, the
There is also a significant increase in activity in the pond at more rapidly the young develop. The fry, which measure less than
⁄4 in (0.5 mm) long on hatching, are nourished
1
this time, as the males chase the females relentlessly, often at first by their egg sacs. After a few days, they
butting or nuzzling against them. are free-swimming and actively seeking food.
Breeding strategies
Coldwater pond fish show no long-term pair-bonding; any
pairings that do occur are purely temporary. Fertilization is Goldfish eggs
external, with eggs and sperm being released into the water Embryo
simultaneously. Most pond species, including goldfish and koi,
are egg-scatterers. They randomly discharge their sticky eggs, Goldfish embryos can
which either sink to the substrate or attach to the stems and be seen curled up inside
leaves of aquatic plants. Only a small proportion of eggs will be their eggs in the close-
fertilized, so the fish compensate by producing large numbers up view above. The
eggs usually develop
of them—up to 400,000 per spawning in the case of koi. on oxygenating plants
After spawning, egg-scatterers have no further involvement (left), held in position
with either their eggs or offspring, but some pond species take by their sticky coating.
more care to ensure that the maximum number of young will
survive. The Fathead Minnow (see p.360), for example, lays its Transparent body
eggs in caves or under rocky overhangs in order to hide them
from predators, while male sticklebacks keep a protective Newly hatched
goldfish fry hide
watch over both their eggs and the newly hatched fry. among vegetation
for about two months.
Early life of fry By the time they
The reason that coldwater fish spawn in the spring is that this is emerge, they have
dark-colored bodies
the time of year when conditions are most favorable for the to camouflage them
survival of the young. The algal bloom that grows in spring, and in their murky
which is often cursed by fishkeepers, is actually crucial to the surroundings.
survival of the fry, since it provides them with their first food.
The young fish eat not only the algae but also the microscopic
creatures called infusoria (see pp.67–68) that live among them.
Dragonfly larvae, water boatmen, and many other
pond invertebrates—not to mention fish (including
the fry’s own parents)—will readily prey on
the young fish. As a result, the fry spend
most of their early weeks hiding
among aquatic vegetation,
rarely straying far from plant
cover. It can take between
one and seven years for the
fish to reach sexual maturity,
depending on the species and the
temperature of the water in the pond.
The full coloration of goldfish usually takes six months or
more to develop, as you can see from these silvery-green juveniles.
In a few cases, individuals do not color up at all but remain dark,
while others change completely within two months of hatching.

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