From pregnant seahorses to starving mouthbrooders, some fish fathers go to extraordinary lengths to raise their young. Discover the remarkable parenting strategies that have evolved beneath the surface.
When it comes to parenting, fish and other aquatic animals have a reputation for being somewhat hands-off. After all, many species simply scatter eggs and swim away, leaving their offspring to fend for themselves. Or worse yet, some dads decide their offspring would make a tasty snack.
But not all fishy fathers are bad dads.
Across rivers, lakes, reefs and even muddy estuaries, some males go to extraordinary lengths to protect, nurture and raise their young. Others have evolved parenting strategies so bizarre they seem almost unbelievable. Let's look a little closer at some of these unbelievable dads.
Starting With Seahorses
Perhaps the most famous of all the dads in the sea are the seahorses. They do things a little differently, and it is the male that carries the offspring and gives birth to the live young – something my wife regularly reminded me of while she was pregnant.
After courtship, the female deposits her eggs into a brood pouch on the male's abdomen. He then fertilises the eggs and carries them for the full duration of the gestation. He provides the developing brood with oxygen, nutrients – via a rudimentary placenta – and protection from predators.
When the time comes, the male births his offspring after experiencing powerful muscle contractions. Broods vary greatly in size, dependent on the species and size of the parents.
Seahorse dad with offspring - Photo by Shutterstock
Related article: Keeping Seahorses in the Aquarium
Mouthbrooding Males
How do fish keep their offspring safe if you don't have a pouch to keep them in? Well, many fish use another part of their body to keep their eggs in until they hatch: their mouths. Mouthbrooding is practised by a wide range of fish, and in some species (Malawi cichlids are a common example) it is the female that takes on this role. However, there are plenty of examples of some fantastic fathers that dedicate large chunks of time to brood their offspring in this way.
Male Betta albimarginata - Photo by Alex Bell
Betta albimarginata are one of a few mouthbrooding Betta species. Males will hold the eggs for 14-21 days, depending on temperature, and they will usually not eat for the duration of this. In fact, they are such dedicated dads that they can drive themselves into starvation by mouthbrooding too often. Aquarists occasionally have to separate the male and female to prevent them breeding again to allow the male to put on some weight again.
It is not just freshwater fish that show paternal mouthbrooding. There are plenty of familiar salty species that protect their eggs in much the same way.
Banggai cardinalfish holding fry - Photo by Shutterstock
Cardinalfishes are a prime example, with males rotating the eggs routinely for up to 30 days while they develop in his mouth. This is a wonderful sight in a reef tank, as towards the end of the incubation you may be able to see tiny cardinalfish eyes within the male's mouth. Similar to the Bettas, male cardinalfish don't eat while they are brooding.
Bubble Nests Require Dedication Too
As we mentioned the mouthbrooding Betta species, it would be wrong to not give the bubble nesters a mention. While the males can still feed during incubation, bubble nesting males still put in a lot of effort.
The male constructs an elaborate floating raft out of mucus-coated bubbles for the eggs to sit in. Once spawning is complete, he picks up the eggs from the substrate and transfers them to the nest for safety, fiercely defending it from potential predators. He also meticulously repairs the nest while also collecting any eggs or fry that fall down, returning them to the safety of the bubbles.
Male Betta splendens under a bubblenest - Photo by Shutterstock
It is not just Betta species that bubble nest, many Anabantoidei perform this behaviour, including gouramis, paradise fish, and snakeheads. In fact, there are even catfish that create bubble nests, the common example being the hoplo (Megalechis thoracata).
The Stickleback Architect
Male three-spined stickleback (Gasterosteus aculeatus) also build nests for their offspring, but they don't use bubbles.
During the breeding season – spring to summer – males develop bright breeding colours and begin constructing nests from plants, fallen leaves and algae. These natural materials are glued together using a protein-rich secretion produced by the kidneys, called spiggin, creating a surprisingly sturdy structure.
Male three-spined stickleback in breeding colours - Photo by Shutterstock
After enticing a female to lay eggs inside, the male fertilises them and takes sole responsibility for their care, chasing away the female. He continuously fans the eggs with his fins to ensure they receive plenty of oxygen-rich water and aggressively defends the nest against predators and rival males. The eggs hatch after around seven days.
Related article: Mighty Blighty: Set up a tank for sticklebacks.
More Mucus
Bubble nesters use mucus to build bubbles, stickleback produce an adhesive like protein for their nests, but discus use bodily fluids for a completely different purpose.
Both male and female discus produce mucus secretions from the epidermal layer of their skin. Their offspring graze on this mucus from their flanks once they are free swimming, which is an impressive and fascinating thing to witness in the aquarium as clouds of fry swarm around the adult discus. These secretions are made up of a wide range of proteins which provide the fry with the essential nutrients for their early development.
Discus fry feeding on both parents - Photo by Shutterstock
Discus parental care extends far beyond the mucus, with parents protecting both eggs and fry religiously from potential predators. While the male is not the sole caregiver, unlike the other examples above, this is a great example of how shared responsibility reduces the burden on one individual.
Parenting Beneath The Surface
Some carry their young. Some build them homes. Some sacrifice meals, while others put themselves at risk by driving away potential predators. The fish fathers put in a tremendous amount of effort, and despite it all, many of their offspring will never make it to adulthood.
While some fish may still opt for the "scatter and forget" approach to parenting, these species show just how far evolution can take parental care. Their dedication proves that life beneath the surface can be every bit as complex – and occasionally as exhausting – as life above it.
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