fish behaving badly
Tuesday, September 22nd, 2009
On this week’s Naked Scientists we had behavioural ecologist Rebecca Kilner in the studio telling us about the extraordinary things cuckoos get up to. Duping other species into rearing your babies for you is undeniably a crafty way of going about life. But it’s not just cuckoos that do it, she told us. Fish do it too.
Namely the cuckoo catfish, a beautiful spotty fish from Lake Tanganyika.
Cuckoo Catfish. Photo by Johnny Jensen
Obviously, its name is a bit of a giveaway. And yes, technically this is a freshwater species – not an ocean inhabitant – but I was so amazed when I found out more about this fish that I decided they deserve space on wild ocean blue (and don’t they look a bit like goat fish?).
For starters, cuckoo catfish hang around cichlids, those famously diverse inhabitants of the great lakes of the African Rift Valley. And they get rather excited by the sight and smell of mating cichlids. So excited in fact, that male and female catfish rush in and cast their own eggs and sperm among the cichlid eggs on the lake floor (where they live as far down as 100m below the surface). The catfish also gobble up a few of the cichlid eggs while they are at it.
Lake Tanganyika as seen from space
The unlucky cichlids are mouth brooders, which means that seconds after the eggs are fertilized the female cichlid slurps them all up and incubates them inside her mouth. Cichlids can’t distinguish their own eggs from the impostors’ so they all get scooped up together.
Can she still eat with a mouth full of growing babies? Apparently not very well. By the time the babies have vacated their mother’s mouth, they leave her underweight and hungry.
And it is not simply that the wily catfish leave their young in the care of the cichlids. They go one step further.
The cuckoo catfish young have evolved to hatch earlier than the cichlids. When they do, they instinctively eat the cichlid eggs and any cichlid fry that have hatched, eventually leaving nothing but catfish fry in the duped cichlid’s mouth.
The cichlid mother is so oblivious to the fraudsters she is nurturing that she will suck the young catfish back into her mouth if they wander outside.
Cuckoo Catfish. Photo by Johnny Jensen
Cuckoo catfish are popular with aquarium keepers, who have discovered that they don’t have to pass their eggs on to cichlids. Their eggs get on perfectly well if they are simply laid on their own on the tank floor.
why, why, why?
It might like seem like a foolish plan to trust your offspring to a total stranger. Imagine the human equivalent! But it obviously does make sense because so-called brood parasitism has evolved in several different groups of animals.
And the reason it works is because for many animals raising youngsters is difficult and costly: feeding them, keeping them safe without risking your own neck, all sorts.
So even if you occasionally get caught out, it can pay off in the long run to palm your babies off on someone else while you head off and make more babies elsewhere.
I give you the cuckoo catfish. All in all, a crazy and wonderful animal. And yet another perfect example of natural selection driving the evolution of something brilliantly adapted to a certain way of life.
In detail:
- Cuckoo catfish, Synodontis multipuncata, can live for up to 15 years.
- Females grow bigger than males, up to about a foot long.
- They are the only fish known to be brood parasites.
- Fishbase entry
On this week’s Naked Scientists we had behavioural ecologist Rebecca Kilner in the studio telling us about the extraordinary things cuckoos get up to. Duping other species into rearing your babies for you is undeniably a crafty way of going about life. But it’s not just cuckoos that do it, she told us. Fish do it too.
Namely the cuckoo catfish, a beautiful spotty fish from Lake Tanganyika.
Cuckoo Catfish. Photo by Johnny Jensen
Obviously, its name is a bit of a giveaway. And yes, technically this is a freshwater species – not an ocean inhabitant – but I was so amazed when I found out more about this fish that I decided they deserve space on wild ocean blue (and don’t they look a bit like goat fish?).
For starters, cuckoo catfish hang around cichlids, those famously diverse inhabitants of the great lakes of the African Rift Valley. And they get rather excited by the sight and smell of mating cichlids. So excited in fact, that male and female catfish rush in and cast their own eggs and sperm among the cichlid eggs on the lake floor (where they live as far down as 100m below the surface). The catfish also gobble up a few of the cichlid eggs while they are at it.
Lake Tanganyika as seen from space
The unlucky cichlids are mouth brooders, which means that seconds after the eggs are fertilized the female cichlid slurps them all up and incubates them inside her mouth. Cichlids can’t distinguish their own eggs from the impostors’ so they all get scooped up together.
Can she still eat with a mouth full of growing babies? Apparently not very well. By the time the babies have vacated their mother’s mouth, they leave her underweight and hungry.
And it is not simply that the wily catfish leave their young in the care of the cichlids. They go one step further.
The cuckoo catfish young have evolved to hatch earlier than the cichlids. When they do, they instinctively eat the cichlid eggs and any cichlid fry that have hatched, eventually leaving nothing but catfish fry in the duped cichlid’s mouth.
The cichlid mother is so oblivious to the fraudsters she is nurturing that she will suck the young catfish back into her mouth if they wander outside.
Cuckoo Catfish. Photo by Johnny Jensen
Cuckoo catfish are popular with aquarium keepers, who have discovered that they don’t have to pass their eggs on to cichlids. Their eggs get on perfectly well if they are simply laid on their own on the tank floor.
why, why, why?
It might like seem like a foolish plan to trust your offspring to a total stranger. Imagine the human equivalent! But it obviously does make sense because so-called brood parasitism has evolved in several different groups of animals.
And the reason it works is because for many animals raising youngsters is difficult and costly: feeding them, keeping them safe without risking your own neck, all sorts.
So even if you occasionally get caught out, it can pay off in the long run to palm your babies off on someone else while you head off and make more babies elsewhere.
I give you the cuckoo catfish. All in all, a crazy and wonderful animal. And yet another perfect example of natural selection driving the evolution of something brilliantly adapted to a certain way of life.
In detail:
- Cuckoo catfish, Synodontis multipuncata, can live for up to 15 years.
- Females grow bigger than males, up to about a foot long.
- They are the only fish known to be brood parasites.
- Fishbase entry