Parental Care
Parental care must have been, doubtlessly one of the most significant steps in
animal evolution.
Scientists have described it as any type of behavior, after fertilization,
which promotes an improvement of the reproductive success of the offspring
(Clutton-Brock, 1991).
However, no matter how normal it looks to us mammals, not all of the animals
species take care of their Offspring.
Only few invertebrates, mostly spiders and scorpions give some kind of
protections to their descendents.
Among reptiles parental care is more the exception than the rule, leaving birds
and mammals, as the only animals that, with few exceptions, raise their
offspring until they can live by their own.
However parental care is not so widespread among fishes.
Only twenty percent of the fish species provide some kind of parental care.
Most of the times, after being fertilized, eggs are left on their own, floating
on the surface of the ocean, adhered to water plants or scattered among the
bottom stones, looking for quantity instead of quality as a breeding
strategy.Those species count on a huge number of unattended eggs or fry will
still manage to produce a sustainable number of adults no matter they are left
on their own in a world full of hazards and predators.
But, on the other hands, fishes are the animals that show the mostdifferent
strategies to help the fry to survive their first stages.
Parental care means several changes to fish breeding, starting with clutch
size.
A wild carp, for example can lay over 30 000 eggs, hidden among plants near the
bottom, but it is unlikely that even the most devoted parents could handle such
a school.
Not the fiercest pair of wolf fish (Parachromis dovii) could drive predators
away from a cloud of tiny fry that would spread for several square meters.
In terms of biologic efficiency, for parental care species, it could be more
productive to protect a limited number of fry that just releasing a huge number
of eggs defenseless among the bottom pebbles.
Of course that different strategies work differently for each
specific environment. Temperature, potential hiding spots, water
movements, abundance of predators among other factors can play a role in which
path is more efficient in a given habitat.
Perhaps one of the most extended strategies are
related to substrate spawner fishes, that lay their eggs on rocks, logs and
other though surfaces.
Those species tend to have some sort of territorial display to keep potential
predators, or dangerous conspecifics, away from their eggs and larvae.
Among those species, we find many cases of biparental protection, as in the
case of many cichlid species.Quite often the male takescare of the territory,
patrolling around the borders, and the female stays closer to the fry, although
parents exchange duties when one of them takes a break to search for food.
But despite the well deserved fame of cichlids for their devotion for family
life, there are many other fishes that watch over their offspring.
Badis, for example are small fishes, barely reaching the two inches long, but
despite their size, they are brave when it comes to guard their breeding .Once
the female enters the burrow where the male is, the pair spawns after a brief
courtship dance where they swim around each other and lock jaws.The male then
guards and defend the eggs but will only look after the fry for a short time
until they are able to swim.
Most of the times, only the male is in charge of the spawn, as in the case of
the European stickleback, of the genera Gasterosteum that builds a nest with
plants and debris, where several females lay their eggs.
The male guards the nest after fertilization, doing maintenance, helping to
keep the structure together with a sticky substance secreted from the kidney
and fanning the eggs to drive rich oxygen water on them. The interesting point
in this species, is that the glue-like secretion has
been found to have antibacterial properties, inhibiting the growth of some
bacteria near the eggs and increasing thehatching rate of the fry. (T.J.
Little, M. Perutz)
Another solitary guardian is the male Wolfish (Hoplias malabaricus), that digs
a hole in the sandy bottom of the rivers where eggs are laid.Female plays no
role here after spawning and the male is in charge of defending the nest and
the eggs until they hatch and disperse. As the circular nest is digged always
in shallow waters, the fierce behavior of the wolfish has caused attacks to
some unaware fisherman with painful bites on their feet.However, recent studies
show that in some cases females remain close to the nest, helping the male to
chase away other fishes. (Prado and Gomiero)
Many catfish, like Ancistrus or Sturisoma species, guard the eggs
that are laid in caves, under rocks or logs.The males covers the eggs
with the body, keeping them out of sight, and rejecting any potential threat
like crabs. When hatching time arrives, the father may even chew the eggs
membranes to help the larvae to emerge.
The male is in charge guarding the spawn during the incubation but the female
may remain in the area even though she is not allowed to get too close.
Those are some of the many cases in which the father takes care of the eggs
until they hatch but tends to loose interest when the fry begin to swim and
disperse.
Protection is here strongly connected to the territory, the nest and thespawn,
but has a rather weak response towards the newborn fishes.They will only be safe as long as they remain near the nest.
Scientists have found that only twenty percent of parental fishes protect the
eggs and afterward take care of the resulting fry.
In such species, males aggressively stake out territories, prepare a spawning
site, and court passing females.The males usually tend to defend the eggs only,
although in a few cases some attention may be granted to newly-hatched fry for
a day or two.
One of the reasons might be that for some species it could be more productive
to raise several successive batches instead of protecting only one until they
are fully independent.
This is the case of many anabantids that build a bubble nest, such as the
Gouramis of the Trichogaster genera.Males can spawn with different females as they
approach the bubble nest, producing consecutive batches with embryos of
different development stages sharing the nest at the same time.
Male Bettas act in a similar way.As the fry grows, they start to leave the nest
in search for food, and the male will try to bring them back to their home,
collecting them and spitting back among the bubbles.But the young ones will
eventually start to disperse and the father will give up, distracted for the
care of new fertilized eggs, younger larvae, and courting newfemales.
Maternal care in fishes is quite uncommon. In many fish the cost of parental
care are higher for females than for males.Protecting eggs or swimming fry
means not only a higher risk of being hurted or killed by a predator, but also
minimizes the chance of the fish to feed in the amount he needs to keep proper
condition for future spawnings.
Since producing eggs for a female demands more energy than producing sperm for
a male, paternal care could have evolved as the most frequent way, since males
lose less from parental care than females do, and could recover breeding
condition much faster after finishing their family duties.
An interesting exception is the Antarctic plunder fish, Harpagifer bispinis , that is found in shallow rubble coves along the
shore. The female cleans a patch in the ground to be used as nest, where she
will remain taking care of the eggs alter fertilization. She cleans the eggs
and keeps predators away while waits for the hatching time, something that, in
the freezing waters where she lives, can take even five months, perhaps the
longest brooding period registered for any fish.
Cold water seems to trigger maternal instinct in fishes since the icefish
Chionobathyscus dewitti female takes charge of the fertilized eggs, that stick
together in small groups around her pelvic fins.The females have been
foundcarrying the cylindrical batches of eggs at depths of 1300 mts and more.
In those species where maternal care is found, mouthbrooding is the most common
strategy.
Mouthbrooding could be a safe way to protect the offspring. The adult fish can
hide among rocks or plants with the fry in the mouth, instead of confronting
predators or bigger fishes. But at the same time is one of the most extreme
forms of parental care since one or both parents must starve during the
process, delaying even the production of new eggs.
Although mouthbrooding reaches it´s peak among the cichlids of lake Malawi, it is not restricted to this group of fishes.
Some catfishes also guard their eggs and fry in the, like those of the family
Ariidae, also called “crucifix catfish” with the males being in
charge of the brooding duties, and the Mustache Catfish, Phyllonemus typus,
unique in its feature of being reported as a bi-parental mouthbreeder.Eggs and
hatched fry of this species are kept in the parent’s mouth and once they
have absorbed the yolk-sac, they release the young ones while they feed among
the rocks while male and female watch over them.
Arowanas are another example of aquarium fishes that protect their offspring in
the bucal pouch for up to forty days, plus a transition period during which the
fry may leave and enter the mother’s mouth in case ofdanger.
Many Anabantids follow the same pattern, as in the case of the chocolate
Gourami Sphaerichthys osphromenoi and Betta edithae among other species.The
spawning sequence of this small Betta is fascinating, with the fertilized eggs
first being hold in the anal fin of the male and then pick by the female and
spit at the mouth of the male to be incubated.
Even some saltwater fishes. like
the Banggai Cardinal fish, a rather small and colorful creature from the Indo
pacific seas that breeds often in aquariums, protect their offspring that
way.It is also the male that holds the eggs for about twenty days and will then
take care of the fry for a few days.
It is interesting to notice that mouthbrooding has evolved separately in
different fish species, fish that are not related,
live in different locations and have no common ancestors. It has developed as
an effective breeding strategy independently on all these species.
Some species carry the eggs with them enabling them to escape if a predator
suddenly appears. We can see examples as the sucker mouth armored catfishes,
Loricariitchthys, that carry the eggs attached to a large membranous structure
on the male’s lower lip, that turns wider and smoother in breeding
males.This is particularly useful for species those species that live in open
sandy areas with few hiding spots available.Another mobile trick is performed
by some cichlids of the genus Aequidens that lay their eggs on submerged tree
leaves, so they can move the whole spawn whenever they feel threatened, by just
grabbing the stem with their mouth and swimming away to a safer zone.
Ovoviviparous fishes could be considered as a variation in the moving eggs
strategy, since the embryos are carried the inside the body, allowing the
mother to escape from predators without abandoning the offspring.
Guppys, swordtails and other poeciliids use this adaptation along with
seahorses and pipefish, four eyed Anableps, halfbeaks and several sharks.
Protected inside the mother, the newborn fry go through the most fragile stage
of fish life, the so called wigglers, where the little ones lay in the bottom,
still unable to swim or fed.
When the ovoviviparous fish are finally born, they have absorbed the yolk sack,
are ready to feed and able to swim and avoid perilous jaws.
The most extreme example of moving the eggs would be moving them out of the
water.The splashing tetra, Copella arnoldi is an
unique fish that spawns on the leaves that grow above their south American
waters.
As soon as the male has managed to attract a female, they line side by side and
leap out of the water together, attaching themselves to the leaves with a fins.
Before falling back to the water,they lay and
fertilize between six and ten eggs.When two hundred or more eggs had been laid,
the males looks for a spot from where he watches over the eggs, and splashes
them with his tail from time to time to keep them moist.He holds his
surveillance for about three days, until the fry hatch, fall to the water and
disperse.
Another surprising way to keep the offspring safe is used by the Asian
bittering of the genus Rhodeus.The females of those fishes lay their eggs
inside freshwater mussels and clams.A large oviduct, measuring up to six
centimeters enables them to deposit the eggs inside the shell using the siphon
of the mollusk .The male releases the sperm near the clam and it is driven
inside by the feeding current.After hatching, the fry remain inside the
shelter, where they are safe and receive a continuous supply of food drawn in
by the clam.
Although fishes don’t bring food to their offspring, like birds do, some
help the young ones to get to their first meals.Discus are famous for producing
skin mucus on their sides from which baby discus feed. There are testimonies
indicating fry from several other cichlids species that eat some mucus from
their parent’s body as a complement to their diet.
Species of Cichlids are known for other ways to help their babies get some
extra food stirring the gravel, in order to turn up edibleitems for their
young.
Some pairs can be seen when herding their school, performing “fin
digging”, rubbing the belly against the bottom in order to raise small
snacks for the fry to feed.
Many years ago, I had a pair of pink convicts that spawned in my tanks several
times.The male had an amazing habit that he displayed when watching over the
school of tiny convicts.
He would grab a stem of Myriophyllum plant with his mouth and move it above the
cloud of feeding fry.When doing so, small pieces of food (algae, flakes
fragments) would fall from the leaves and were eaten by the young fish.Every
time the group of babies moved to a new area of the tank, he would take the
plant again and place directly above the school.
Nowadays I’m not sure if the male was actually “shaking the
tree” trying to feed his offspring, or just trying to keep them hidden
among the leaves, with the falling food being just a side effect. Whatever were
his intentions, I have no doubt it was a deliberate act he performed in order
to help his young ones.
Another case of the many surprising behavior fish can show when it comes to
help their descendants to survive until they are able to get along by
themselves. Small miracles of a fish family life we can be lucky enough to
witness in our own tanks.