Frogfish lure their prey with a built-in fishing rod and bait

The world beneath the ocean waves is home to countless mysteries, and frogfish are among its most intriguing inhabitants.

These elusive masters of disguise, a subgroup of anglerfish, have evolved unique adaptations to thrive in diverse marine environments and make their presence felt in fascinating ways.

Frogfish are famously known for their deceptive charms. The clever and effective use of elaborate camouflage allows frogfish to blend seamlessly with their surroundings and renders them nearly invisible to unsuspecting prey.

Their dine-and-dash tactics revolve around catching small fish and crustaceans off guard. In this approach, they embody the notion that everything is fair in love and war – and survival.

The role of frogfish dorsal fins

The secret behind the successful hunting strategy of frogfish lies in the magic of their dorsal fins, which perform crucial functions.

While the dorsal fins located in the center of their bodies are used to exhibit threatening behavior, the back fin offers stability and propulsion while swimming.

The real showstopper, however, is the front dorsal fin or the “illicium,” which is essentially a rod-like structure with a lure or “eska” that bears an uncanny resemblance to a clam worm.

Much like a seasoned angler, the frogfish uses the illicium to wave the eska around as a tantalizing bait.

The ill-fated prey fish are deceived into mistaking the eska for a meal, only to be engulfed by frogfish in a single, swift gulp. Despite this seemingly simple hunting technique, the mechanical processes behind it are complex and curious.

Neuronal mechanism for fishing behavior

In a recently published study, researchers from Nagoya University’s Graduate School of Bioagricultural Sciences led by Professor Naoyuki Yamamoto set out to explore the unique neuronal mechanisms that drive the unusual hunting behavior of frogfish.

The scientists discovered a population of specialized motor neurons in the illicium, which they referred to as “fishing motor neurons.”

It turns out that these motor neurons enable the fishing behavior of frogfish by making the illicium different from the other dorsal fins.

To investigate, the researchers used tracer injections to visualize motor neurons that were situated in the ventral horn of the spinal cord. These particular neurons control swimming movements.

Migration of frogfish motor neurons

Yamamoto’s team was amazed to find that the illicium’s motor neurons reside in the dorsolateral zone. These are distinct from the neurons of the second, third, and fourth dorsal fins, which are located in the ventrolateral zone of the ventral horn.

The researchers compared the motor neurons of frogfish with those of white-spotted pygmy filefish – a species that uses the first dorsal fin for warding off competition and predators rather than for fishing.

The results suggested that the motor neurons used by frogfish for hunting had shifted during the evolution of their function.

“This is an extremely rare case in which motor neurons for the illicium were originally dorsal fin motor neurons, but their location was shifted to serve a role completely different from their original function,” said Yamamoto.

Implications for human evolution

These fascinating revelations, though seemingly exclusive to the marine world, may also be relevant to life on land. According to Yamamoto, these findings shed light on human evolution as well.

By drawing parallels between the motor neuron organization in frogfish and that in other vertebrates, this study highlights the evolutionary connections shared across diverse species.

“While we, as land animals, do not have fins, our forelimbs and hindlimbs are similar to the pectoral and ventral fins in the light of their distribution in the spinal ventral horn, and our ancestors also once had dorsal fins,” noted Yamamoto.

“The organization of different groups of motor neuron groups is similar among vertebrates. In vertebrates, there are several species with highly specialized behavior.”

“Our study provides a new point of view on motor neurons, and we hope it prompts similar studies in other species that lead scientists to understand the rules that govern their organization.”

Yamamoto hopes that these findings will serve as a catalyst for further research into motor neuron organization across species, which could deepen our understanding of the intricate connections within the evolutionary tapestry of life.

The full study was published in the journal Journal of Comparative Neurology.

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