Peek into the world of tiny fish and their short, challenging lives packed with colour, diversity, and extraordinary behaviour
Text by: Chetana Babburjung Purushotham
Peek into the world of tiny fish and their short, challenging lives packed with colour, diversity, and extraordinary behaviour
I wish to introduce you to the lesser known but highly abundant tiny fish in the ocean. From dragonets and damsels to silversides and fusiliers, there is a world of fish that we fail to notice in our pursuit of larger marine fauna. In my experience, the small fish appear to welcome us into the ocean, their eager schools accompanying us as we swim, dive, or snorkel through the water. A closer look at tiny fish sitting amidst the coral will reveal a tapestry of shapes, colours, and exquisite designs. In areas of the ocean that are overfished or where corals are bleached, many charismatic species have dwindled, but these “thumbelinas” hold the fort as the ecosystem gradually rebuilds itself.
There is a lot we know about small marine fish from a fisheries perspective. For instance, sardines, anchovies, sprats, halfbeaks, and fusiliers are small pelagic (ocean-dwelling) species that swim in schools as they feed on plankton. They form the primary diet of a host of large oceanic animals, including tunas, barracudas, cod, marine mammals, and even seabirds, and are grouped as “forage fish”. Forage fish have historically played an important role in the fisheries sector as food for larger fish. In recent decades, forage fish have been increasingly targeted for human consumption and producing “fish meal” for the poultry and pet food industries. Many of these small-sized species are also called “baitfish” in the recreational fishing industry, where they are used to lure larger fish like groupers, tunas, marlins, and swordfish.
For cryptobenthic species, i.e., live close to the ocean floor, life is fast and rather short. Blennies, cardinalfish, and gobies, for instance, are important prey for larger reef fish and have rapid lifecycles to replenish the population that gets eaten. Scientists have found that overfishing and ocean warming are causing a decline in this once incredibly abundant collection of fishes.
There are thousands of species of thumbelinas of the sea, the smallest being under 10 mm in length and the shortest lifespans being a mere few weeks. Yet, their short and challenging lives are packed with colour, diversity, curious biology, and some of the most extraordinary behaviour seen in the ocean. Let’s take a peek into their world.
On a coral reef, longnose filefish (Oxymonacanthus longirostis) look like a 10-cm-long brightly coloured crayons. They live among live branching coral (Acropora) for two evolutionarily fascinating reasons. First, they feed exclusively on live polyps of Acropora corals. Eating other coral polyps affects their reproductive success. Second, Acropora polyps, once digested, create chemicals that make the fish smell exactly like the prey they consumed. This works well to conceal them from larger reef predators. Photo: Umeed Mistry Cover photo: Longnose hawkfish (Oxycirrhites typus). Photo: Umeed Mistry
Jawfish (Ophistognathus sp.) are small, slender fish with broad jaws. They predominantly live inside burrows they make in sandy habitats. Their mighty jaws help them excavate, dig deeper, carry more sand out and fortify the burrow opening with shell and coral fragments. The male jawfish’s jaws also have the incredibly important function of acting as an incubator. Soon after mating, a female lays a clutch of eggs that is immediately scooped up by the male and kept safe in his mouth until they are ready to hatch. This takes between a few days to weeks, depending on the species. During this period of “mouth brooding”, the male will not eat, and his movements are restricted to tossing the eggs around inside his mouth to keep them aerated. Once hatched, the young ones exit the safe chambers of their father’s mouth but stay close by until they become adults. Photo: Umeed Mistry
Few sights are as hypnotising as the synchronised shimmer of shoaling damselfish playing now-you-see-me, now-you-don’t around coral. Damselfish are particularly small and vulnerable to predation. Hanging out in dense shoals provides safety in numbers. To further reduce the risk of capture, they live in partnership with corals like Acropora. The intricate arrangement of coral branches gives the entire shoal of fish plenty of room to hide from the slightest threat. Their poop is sufficient nourishment for the coral to continue renewing this partnership. Videos: Umeed Mistry
Life in the big blue ocean can be terrifying, especially for smaller fish. With no rocks, seagrass, or algae to provide shelter, these fish only have each other. And together, they can put up quite a fight in the face of predation. When predators like trevally, tuna, billfish, or even dolphins start to corner them, schooling fish make denser and tighter groups, often called “bait balls”. This is a last-ditch effort to hide in a crowd, but a few tactics could still help them escape. For instance, predators can get confused when their prey rapidly split into small schools and regroup elsewhere, swiftly dispersing in several directions only to turn into a ball within seconds again. The silvery sheen on the flanks of silversides, fusiliers, and anchovies can distract predators, making it harder for them to chase individual fish. Although this phenomenon looks pre-meditated, schooling is a behaviour that emerges from split-second decisions made by each fish that participates. Video: Adhith Swaminathan
Golden sweepers (Parapriacanthus ransonneti) may not be more than 10 centimetres long, but when hundreds and thousands of them aggregate together a superorganism forms. A school of golden sweepers from a distance can be mistaken for a swarm of bees, except you are underwater! These pinkish-golden fish with large eyes are nocturnal hunters of zooplankton, but during the day, their priority is to stay safe. They achieve this by huddling together in dark coral caves, overhangs, and narrow swim-throughs between large rocks. A school of sweepers can become dense enough it be an opaque wall. Video: Umeed Mistry
Anthias (Anthiadinae) are strikingly gorgeous fish — vibrant with design streaks, spots, and tassels. Hundreds of them can turn a coral reef into a dazzling kaleidoscope of intense colour. Despite their abundance and the numerous adjectives used to describe their beauty, regular divers and snorkellers tend to miss anthias. We may swim over or past them, and still miss them. I wonder if it’s because they’re too common to warrant our attention. Photo: Umeed Mistry
Seamoths (Pegasus sp.) are seemingly mythical creatures of the ocean floor. Small flattened fish, they have narrow heads ending in a snout and colours that help them blend in with the sand and rubble. Like tiny planes on a runway, seamoths gracefully glide through their habitat, looking for tiny invertebrates to slurp up. Photo: Umeed Mistry
Can fish experience curiosity and wonder? We sometimes think of fish as swimming around with arbitrary movements, like background characters in a video game. We may not agree about whether fish are self-aware, sentient beings, but what is irrefutable is that they have social lives. They recognise one another, their peers, and competitors. They map their surroundings, memorise routes and maintain relationships. And we can observe this in real-time. This assembly of blennies was seen in a tidepool barely inches deep, their vigilant eyes locked on the photographer. Photo: Umeed Mistry
Dragonets (Callionymidae) are some of the tiniest fish we come across on the ocean floor. The grains of sand in this image give us an idea of scale. Quite often, a magnifying lens is required to appreciate the intricate detail of these miniatures. What is surprising about dragonets is the risk involved in their mating rituals. These tiny bottom-dwelling fish are spawners, which means the courting pair must swim up into the open water column until they reach a suitable height before releasing eggs and sperm into the currents. Photo: Umeed Mistry
