Propulsion Power

Studying and observing game fish might sound boring to you, but fish anatomy, physiology, ecology and behavior is actually very exciting. To me it is fascinating information that will help anglers better understand a fish’s particular hunting behavior and strategies, in addition to their interaction with the surrounding environment.


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Permit have a profound sickle tail that helps them hunt with impressive speed and agility. Photo: Pat Ford

Since the dawn of day, anglers have been comparing fish species and their inherent challenge to subdue. Some claim bonefish are strongest pound for pound, while others say unless it has a bill it is bait. While every angler has his or her theory as to why a particular game fish is considered the perfect target, there’s really no definitive way to determine which aquatic predator is the most menacing.

Whether game fish are found offshore, near‑shore, or inshore, the tail is exactly where performance, speed and maneuverability all originate.

When comparing game fish species one must consider like size fish, and ignore the adage of pound for pound. Would you rather get down and dirty with a 425 lb. goliath grouper or the new IGFA all tackle 427 lb. yellowfin tuna? You must then consider the fish’s stamina, hunting tactics and response once hooked. Tuna are known for screaming runs and their ability to dig deep, while tarpon and billfish often jump clear out of the water in an attempt to throw the unfamiliar tether—an act that actually helps anglers subdue fish faster.

While the shape, size and color pattern of any fish is certainly significant and critical in the particular specimens exact role in the aquatic food chain, perhaps the most important component of any oceanic inhabitant is its caudal fin, or tail. Whether game fish are found offshore, near-shore, or inshore, the tail is exactly where performance, speed and maneuverability all originate. A quick glance at a fish’s tail can not only help in quickly identifying a particular species, but understanding the advantages and disadvantages of various tail shapes provides valuable insight on how and where to target your favorite game fish.

We all know that the caudal fin is a fish’s primary source of propulsion, however not everyone knows that tail shape is always in direct correlation to the individual fish’s preferred habitat and hunting characteristics. This explains why tails come in a wide variety of shapes and sizes depending on the lifestyle of the species and the environment it prefers.

Swimming is a basic fundamental for game fish and most species create thrust by rapidly beating their tail from side to side while alternately curving, or flexing the remainder of their body in rapid oscillations. The tail completes the action by displacing enough water with each beat to propel the fish forward. But there are exceptions to this rule. High performance, long distance travelers like tuna rely mainly on the movement of their tail for forward momentum, with little to no additional energy expended from the body. It is their overall body shape and swimming efficiency that enables them to make such long distance movements without ever stopping. In addition, many slow moving reef species are capable of delicate, precise movement strictly through their dorsal, pelvic and pectoral fins.

When it comes to the ocean’s top predators, tails may be shaped with a heterocercal or homocercal orientation. Many shark species have different sized upper and lower lobes, making them an example of heterocercal tail shape, while most game fish have homocercal tails, meaning they are almost perfectly symmetrical.

Juvenile or giant, each member of the tuna family is equipped with a thin lunate, or crescent shaped tail like those found on wahoo, billfish and jacks—all extraordinarily fast, agile and successful hunters. Lunate tails provide the perfect propulsion tool for swimming long distances at impressively fast speeds. Aggressive eating machines search far and wide for protein-rich food sources and along with keen eyesight, speed and endurance afford the ability to chase down fast moving prey in open water habitats. These efficient hunters are masters of racing in for the kill and swallowing prey whole with such speed the unsuspecting meal rarely sees the end coming. This is especially true during low light conditions when forage species typically let their guard down.

Lunate tails are thin, lean, and streamlined. It’s scientifically proven that the design is perfect for producing and maintaining impressive speed for great distances. A larger, broader tail and the open ocean predator would likely tire too quickly.

Along with an impressive propulsion system, tuna are also outfitted with small, non-retractable finlets in the back portion of their body behind their dorsal and anal fins. Once the beating tail has established forward momentum, tuna use these finlets, which flex side to side like small rudders, to influence rapid directional changes. The result is a perfectly shaped and highly adapted migratory schooling predator built for speed and endurance. The streamlined body and retractable fins minimize friction while the predator races through dense seawater in a never ending hunt for forage. As you can imagine, migrating thousands of miles is no easy task and requires a tremendous amount of energy, so tuna must have the ability to chase down schools of fast swimming baitfish and squid in an open ocean environment in order to survive.

Tails of reef fish on the other hand, particularly grouper, are shaped differently than open water predators. Grouper are not near as sleek or streamlined, but that doesn’t mean they aren’t equally specialized hunters. Mature grouper are relatively solitary fish that operate in a different environment altogether with confined spaces and complex underwater landscapes including natural and artificial reef formations. They avoid predation and maximize their kill ratio by racing into crevices and under overhanging ledges and coral heads. As they mature, their unsuspecting prey is generally in the same vicinity and often found swimming just feet in front of the merciless killer.

To rule the reef and capitalize on feeding opportunities in the midst of rough bottom terrain, swift maneuverability is far more important than long distance endurance. Unlike torpedo-shaped pelagics, grouper have developed broad shouldered bodies that maximize the ability to quickly lunge forward and instantly change direction. Their truncate, or broad and rounded tail is ideal for both instant acceleration and complex maneuvers, the latter of which is supported by large, oversized pectoral and pelvic fins that act as steering fins and brakes. While they are no doubt incredibly agile, a big grouper on the hunt also has the ability to accelerate from zero to full speed in a fraction of a second. Which such intensity, dogfight maneuverability and a gaping mouth, I can’t imagine being an unsuspecting grunt or tasty crustacean in their crosshairs.

However, because grouper have broad bodies and a rounded tail, they tend to tire quickly. Those of us who have gone head to head with these extremely powerful bottom dwellers know that big grouper dig to the death, but unlike tuna that will easily dump a 30-wide, even a monster black isn’t capable of burning hundreds of yards of line off a reel in a single blistering run.

Clearly, the efficiency and performance of the ocean’s inhabitants varies greatly with unique body and tail shapes that provide each family of fish with advantages and disadvantages depending on preferred habitat and hunting characteristics. In reality, it’s impossible to determine which game fish is really the most efficient killing machine, effective hunter, or hardest fighter. One thing we can all agree on is that observing game fish and understanding their surroundings will undoubtedly make you more successful and knowledgeable in your ongoing pursuit of angling glory.