Specimen Showcase｜Predatory “Plants”
- Hong Kong Biodiversity Museum
- Apr 8
- 3 min read
In the swirling Sargassum seaweed floating on the Atlantic or the Indo-Pacific Oceans, the line between organisms and their environment blurs🌫️. A realm where fish become living seaweed, dancing effortlessly among the ocean's floating forests🌲. Swimming through the intricate floating sargassum seaweed, passing by different species of marine animals, but wait, did a seaweed just eat a fish🐟? Look closer, it is not a seaweed, but Histrio histrio (Linnaeus, 1758) also known as the Sargassum fish perfectly blending in the seaweed, hunting down fish unnoticed thanks to their camouflage, with some of them even larger than the Sargassum fish itself.
Sargassum is a unique floating seaweed habitat predominantly composed of golden-brown algae. This floating ecosystem exists in the open ocean, forming dense mats that provide shelter, food, and a breeding ground for various marine organisms ranging from tiny invertebrates to larger animals like fish, turtles and birds.
Sailing through the Sargassum seaweed, with extraordinary eyesight, you may notice the Sargassum fish. The fish get their name from their close association with the seaweed which they mimic. They have a laterally compressed body shape and can grow up to 20 cm. Different individuals have variable colour and pattern, though usually they have a mottled skin with yellow, green, brown spots. Some even have small white stripes that resemble tiny worms living in the algae, which attract prey that might feed on those worms. To perfect their camouflage, fleshy Sargassum-like appendages cover the whole fish, helping them blend in their habitat.
Sargassum fish belong to a family of fish called the Antennariidae, commonly known as the frogfish. One of the common traits of frogfish is their relative inability to swim - a paradox for a fish❌. Their ambushing nature made them less reliant on swimming, and thus they rarely need to use their fins for swimming. Instead, their fins are used for walking🏃➡️. To do so, they have developed modified prehensile pectoral fins, giving them the ability to cling on Sargassum and climb through the seaweed. They generally move very slowly, but if they need to move a short distance quickly, they can also expel water from their gill opening like a jet🚤, which is located near the base of their pectoral fins, helping them burst forward.
Another common trait of frogfishes is their prey capture strategy. When a potential prey swims by, they will first lock eye contact with it👀, and slowly move towards the target. When the prey moves close enough, it just disappears in a fraction of a second. To depict exactly what happened, we need to revive the scene in slow motion. Right when the prey swims in range, the frogfish expands its mouth, enlarging their mouth cavity by 12 times, creating a significant pressure difference in and out their mouth, quickly sucking in the prey and seawater in their mouth, in just 6 milliseconds! The prey can simply not react in that short period of time, making frogfishes one of the most effective predators in the world.
During the breeding period, male Sargassum fish will follow the female closely, and if the female is ready and accepts the male, they will start breeding. The female will lay eggs around the Sargassum, so the male nearby can fertilize the floating eggs. These eggs can be sheltered in the seaweed, providing shelter for the eggs, and the future juveniles☂️.
Does the Sargassum fish raise your interest in ecology and biodiversity? If your answer is positive, come to the Hong Kong Biodiversity Museum where we have a wide variety of specimens, from corals to mammals, and you can learn more about their fascinating ecology. And if you found this article engaging, share it with your friends and stay tuned for our captivating biodiversity narratives released weekly!
Text: Paco
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