The diverse spawning behaviors of reef fish
Reef fish exhibit a variety of different spawning behaviors. A few examples:
- Most marine fish (and also many marine invertebrates)
release sperm and eggs into the water column. In many reef species pairs
or breeding groups rise rapidly toward the water suface in a spawing rush,
quickly releasing eggs and sperm into the currents before hastily returning
to the safety of the reef . Eggs and larval fish drift in the water currents.
These larvae often look nothing like the adults. They live a planktonic
existence for a few weeks or months, before undergoing a physical transformation
that changes them into miniature versions of the adults. Once this metamorphosis
has taken place, the young fish seek out a suitable reef habitat where
they will settle down and start living a lifestyle more typical of adults
of their species.
- Clownfish and damselfish (such as our green chromis), however, attach
their eggs to rocks, defending them from predators and keeping them clean
until they hatch. The larval fish are then planktonic as described above.
- Male jawfish, on the other hand, carry their eggs in their mouths until
they hatch, at which point the larval jawfish live a planktonic existence
- Banggai cardinalfish males also carry their eggs in their mouths, but
their eggs are very large. Consequently, the young are also very large
and look like miniature adults upon hatching, and they spend no time drifting
as plankton before settling into the seagrass beds where they will spend
the rest of their lives. As a result, this species does not disperse to
new areas very well, and in the wild it is only found in the vicinity of
the Banggai islands near Sulawesi. Fortunately, these fish reproduce quite
readily in captivity, and our Banggai cardinal fish are captive bred.
- How do these marine fish breeding strategies differ from those found
in freshwater fish?
- A few generalities:
- Though many freshwater fish are egg scatterers, and their spawning
behavior is superficially similar to the most common spawning strategy
found in marine fish, in the vast majority of cases the eggs and fry
of freshwater egg scatterers do not drift in the water as plankton.
Generally the eggs either settle to the bottom (as do salmon eggs, which
rest among the pebbles at the bottom of a stream until they hatch), or
the eggs stick to surfaces such as submerged aquatic plants (e.g. goldfish
eggs, and many others). Consequently, when spawning, pairs or spawning
groups of these freshwater egg scatterers generally do not rise into the
water column to release their eggs and sperm the way many marine fish do,
but rather they swim directly over or through the substrate or vegetation
that receives their eggs.
- A great many freshwater fish species exhibit extensive parental
care, which often continues for some time after the eggs hatch. A few
examples: In North American sunfish (and bass), males tend and guard both
eggs and young. Similarly in the diverse cichlid family (which is found
in the New World tropics, Africa and parts of Asia), extensive care is
given to both eggs and fry by the male parent, the female parent, or both
parents, depending on the species. Though a variety of different marine
fish species tend their eggs, extensive care of the young after hatching
is very rare among marine fish species.
- See also: The
strange sex lives of reef fishes