Photo StoryPublished : Jun 15, 2023Updated : Sep 30, 2023
Fish don’t always come in the “textbook” shape we associate with them. Their forms often deviate from the norm, and their uniqueness helps them survive and thrive
Text by: Chetana B Purushotham
Fish don’t always come in the “textbook” shape we associate with them. Their forms often deviate from the norm, and their uniqueness helps them survive and thrive
At some point in our childhoods, the “textbook” or typical shape of a fish embeds itself into our brains. In this image, a fish’s head and tail taper at different ends of the body. The streamlined body usually has a fin at the top and bottom and one eye visible on the side facing us. This shape, we have learned, helps them move easily through water, cutting across currents. However, this textbook fish shape does not always represent the variation and diversity of real fish species. Over evolutionary time, environmental conditions, the food they eat, and the predators they hide from (among other factors) shape fish anatomy, morphology, habits, and behaviour.
Streamlining allows fish to cut through the water, minimising drag, which helps predatory fish get to their prey easier and smaller fish escape faster. While slender and tapering neat ovals help with streamlining, there are many habitats, lifestyles, and survival strategies in which being streamlined is not the most efficient design. There are slower, stockier fish that can hide and manoeuvre better. Eyes looking forward for some fish may be more disadvantageous than eyes on top, and some fish might prefer to sit perfectly still for hours to hunt instead of chasing after their prey. Even various fin positions may serve different purposes.
This story is about the fish often described as “odd-looking”, “peculiar”, “strange”, or even “ugly”. We are saying that their appearance is “unexpected”, “not regular”, and not the textbook fish shape we’re so used to.
Here is a vibrant showcase of some commonly seen odd shapes from the marine world, from cheeked pipefish with elongated tubular mouths to the globular painted frogfish. We take a short journey into the many ways fish forms can deviate from the norm and how their uniqueness has helped them survive and thrive.
Cheeked pipefish (Corythoichthys insularis), at first glance, look like ten-centimetre-long snakes gliding over coral boulders until your eyes notice the gentle movement of their translucent fins and the beating of tiny gills at the back of the head. The most distinctive feature of pipefish is their elongated pipe-shaped tubular mouth. They have fused jaws (no hinges or moving joints) and no teeth, characteristics they share with seahorses. While this morphology might limit the diversity and size of prey they can ingest, pipefish are expert hunters of small crustaceans that they swallow whole. Photo: Umeed Mistry
Reef stonefish (Synanceia verrucosa) are bottom-dwelling ambush predators. They sit like motionless stones on the ocean floor, camouflaged amidst coral and algae, waiting for fish, crustaceans, and sometimes cephalopods (like squid) to come within gulping distance. Stonefish can swallow their prey whole and extremely quickly, using suction created by the pressure difference inside and outside the mouth when they strike. As if to be ever ready to attack, stonefish have evolved an upward-looking face. Their eyes and mouth are placed on the top of the head, not in front. Fins and tails are leathery, adding to the camouflage, but they also help them dig up sand or prop up in awkward crevices in the reef. Providing maximum security to this fish are dorsal, ventral, and anal spines laced with potentially lethal “verrucotoxins” that keep their predators at a safe distance. Photo: Umeed Mistry
The peacock razor wrasse (Iniistius pavo) is a phenomenal escape artist found in sandy areas. The protruding section of their dorsal fin is a clever masquerade helping them pass off as drifting dead leaves or seaweed. When these wrasses sense a threat, they dive headfirst into the sand, digging their way underneath within seconds. Photo: Sahil Lokhandwala
Scribbled filefish (Aluterus scriptus) are large and graceful fish with extremely flattened oval bodies, skirted by gently undulating fins and tapering into long tail fins that move like a paintbrush. Their yellowish-golden bodies are covered in black spots and blue scribbles. Permanently “O” shaped mouths help them feed on algae, seagrass and a host of sessile invertebrates like fan coral, tube worms, hydrozoans, anemones, and tunicates. Scribbled filefish are often seen swimming and feeding in pairs. The best way to observe these shy animals is by giving them space and keeping movement to a minimum. Photo: Umeed Mistry
The painted frogfish (Antennarius pictus) has mastered the art of blending in. If you find it, what first strikes you is its globular appearance and what looks like feet. These are pelvic fins modified into walking appendages. Their body shape and the ability to change colour allow them to masquerade as some of the least fish-like organisms on the reef. The numerous spines and perforated warts on their bodies help them mimic a colony of harmless marine sponges. What lies beneath this spongy disguise is a fish lying in wait, with rod and lure in hand (on its head, to be accurate), ready to suck in fish that get too close. Photo: Umeed Mistry
Crocodile flatheads (Cymbacephalus beauforti) are prominent members of the “camouflaged ambush predators of the ocean” community. Crocodile flatheads employ a strategy called “background matching”, seeking out substrates and structures whose colours and textures they can camouflage with. To do so, they must pay attention to the play of sunlight, degree of contrast, and brightness of objects in their immediate environment to help them hide in plain sight. Flatheads have intricate patterns running along their bodies and fins, right down to their eyes, to help them break up their fishy outline and become seamlessly one with the reef. Photos: Umeed Mistry (1), Sahil Lokhandwala (2)
Seamoths (Pegasus) are exceptionally beautiful bottom-dwelling fish that might remind you of a plane on a runway. A narrow tubular mouth meets a flattened fish with pectoral fins that spread like wings and ventral fins that help it walk on sandy and rubble seabeds. Seamoths are bizarre and beautiful creatures, but we know little about their ecology. Are they rare species or abundant but not given enough attention? The good news is that new species of seamoths are still being discovered. For the recreational SCUBA diving community, coming across a seamoth is truly a precious find! Photo: Umeed Mistry
Batfishes (Platax) are silvery disc-shaped fish with large fins that give them a somewhat triangular appearance and a pair of short, slender, and colourful ventral fins that emerge from below their heads. As juveniles (in the video), they look completely different. This is probably to adapt to the predation risk in their habitats as young fish (mangroves, seagrass meadows, and tide pools). Young batfish have evolved to look and behave like drifting dead leaves and can sometimes be found drifting among miscellaneous floating debris. Most reef fish are indifferent to humans in the water if they are not scared. Batfishes, on the other hand, are quite curious and social. On several occasions, while diving in the Andamans, I have seen batfish leave their school to get a closer look at us, following us and interacting playfully (swimming through our bubbles) before reuniting with their group. The next time you see a batfish while diving, try waving them a “hi!” and see if they respond. Photo: Sahil Lokhandwala (1); video: Samuel John (2)
