by Rucha Karkarey
Where do baby fish come from?
You probably thought about Nemo – the famous clownfish who was raised by his parents in an anemone ‘nest’. Many fish like Nemo rear their young, in makeshift nests. The trusty male seahorse nurtures his partner’s eggs in his stomach. Some strange fish like cardinalfish even rear their eggs in their mouths! But did you know that most coral reef fish do not look after their eggs at all? No, this doesn’t make them bad parents; they are simply confident in their babies’ abilities to survive without their care. They bid farewell to their eggs, as they release them into the water. Ocean currents then transport the eggs hundreds of kilometers away from reefs. It is in the deep, dark, open ocean that these eggs develop and grow into fish babies, called fish fry.
Most coral reef fish have two main life stages: They are born (or rather they hatch) in the open ocean, where they slowly develop into fry over a period of 2-5 weeks . Once the fry are big enough, they make their way back to the coral reef. When they arrive at a reef they look for available spaces to settle in. Once settled, they begin the adult stage of their life.
Journey and the challenges
Now imagine yourself as a small fish fry. Wouldn’t it be fascinating to have the freedom to travel the open ocean? Let me tell you this, the journey of a fish fry is fraught with peril. The vast open ocean has harsh, unpredictable weather and plenty of deadly jellyfish that would love to eat you. For those of you who manage to survive, the biggest challenge is finding a coral reef! Imagine this, amongst everything in the immense ocean, you need to be able to identify the smell and sound of a small reef. Once you identify a direction, you start swimming towards it. Seems tough, doesn’t it?
This isn’t even half the battle. When you finally arrive at a reef, you will be exposed to a whole new set of hurdles. There will be predatory fish lurking in the reef that are waiting to swallow you whole. There will be very few shelters available for you to settle in. After all, coral reefs (like a big city) tend to get very crowded. Food will be scarce, because everyone is eating all the time. To top it all off, you will have to compete with thousands of other fish fry like you to settle down.
The Smartest survive
As you can see, to find and settle in a home is a great challenge for reef fish fry, one that over 90 per cent will fail to meet. So although millions of fry like you will arrive at a reef at the same time, a very small proportion will successfully settle down. In the life of fry, only the smartest survive. But don’t be overwhelmed yet; watch this space for useful survival tips next week!
The phenomenon of fish fry finding and settling into a reef is known as ‘larval recruitment’.
Fish fry feed on tiny, microscopic plants (phytoplankton) and animals (zooplankton) which are abundant in the ocean.
Fry are transparent in the open ocean, which makes them invisible to most predators. Once they settle into the reef however, they rapidly gain colours.
Most fish fry are less than 3 cm in length when they arrive at reefs.
Inspite of being small, fish fry are very good swimmers and can swim against strong ocean currents to reach coral reefs.
In the Lakshadweep islands, massive larval recruitment events of surgeonfish are commonly observed between the months of January and March.
Picture: Tough journey – thousands of surgeonfish fry swimming towards a coral reef in the Lakshadweep islands, to settle down. Credit: Rucha Karkarey