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.