Bigeye Tuna, Allen Shimada, NOAA NMFS OST, Public domain, via Wikimedia Commons

Bigeye Tuna: Everything You Need To Know About Thunnus Obesus

What is Bigeye Tuna?

The Bigeye tuna, Thunnus obesus, is an important pelagic fish species both ecologically and commercially. As a member of the Scombridae family, this fast-swimming predator is a marvel of evolution and adaptation. This article delves into the biology, ecology, and conservation concerns surrounding this incredible species.

Taxonomy and Description

Bigeye tuna belongs to the genus Thunnus, which also includes other tunas such as the bluefin, yellowfin, and albacore. Morphologically, Bigeye tuna is characterized by its robust body, metallic blue dorsal side, and silvery-white ventral side. A distinguishing feature is its notably larger eyes compared to other tuna species, an adaptation to its deep-water habitat.

Distribution and Habitat

Bigeye tuna inhabits tropical and subtropical waters worldwide. The species has a wide distribution range, extending from the Atlantic, Indian, to the Pacific Oceans. It predominantly occupies the pelagic zone, often found in deep waters. Unlike some of its cousins, Bigeye is known to dive to depths greater than 500 meters, possibly in pursuit of prey or to find cooler waters.

Diet and Feeding Behavior

Thunnus obesus is a carnivorous predator, with a diet consisting mainly of cephalopods, crustaceans, and other fish. Their large eyes are an adaptation for locating prey in the dimly lit depths of their habitat. As opportunistic feeders, Bigeye tuna swiftly chase down their prey, using their streamlined bodies for rapid acceleration.


Bigeye tuna are broadcast spawners, releasing eggs and sperm into the water column simultaneously. The exact age of sexual maturity varies but is generally attained by the age of 2-4 years. Fecundity is high, with females producing several million eggs in a single spawning season. However, not all these eggs will reach adulthood due to predation and other environmental factors.

Commercial Importance and Fishery

Bigeye tuna is a highly prized fish in commercial fisheries, especially in the sushi and sashimi market. The high fat content in its muscle tissue gives it a rich flavor, making it a delicacy in many cultures. The global demand has led to extensive fishing, sometimes resulting in overfishing concerns.

Conservation and Management

Over the past few decades, there have been increasing concerns about the sustainability of Bigeye tuna fisheries. The International Commission for the Conservation of Atlantic Tunas (ICCAT) and the Western and Central Pacific Fisheries Commission (WCPFC) are among the international bodies that monitor and manage tuna stocks, including the Bigeye tuna.

Due to overfishing, several measures have been introduced to ensure the sustainability of Bigeye tuna populations. These include quota systems, size limits, and temporal and spatial fishing closures. Furthermore, initiatives promoting the use of circle hooks in longline fisheries aim to reduce bycatch and the unintentional capture of non-target species.

How to Cook Bigeye Tuna

Bigeye tuna, known for its rich flavor and buttery texture, is a favorite among seafood enthusiasts. Here are a few ways to prepare and cook Bigeye tuna to maximize its flavor and texture:

Seared Bigeye Tuna Steaks


  • Fresh Bigeye tuna steaks (around 1 inch thick)
  • Salt and freshly ground black pepper
  • Sesame seeds (optional for coating)
  • 2 tbsp olive or sesame oil
  • Soy sauce, wasabi, and pickled ginger (for serving)


  1. Ensure the tuna steaks are at room temperature.
  2. Season both sides of the tuna with salt and pepper. If you like, press the tuna steaks into sesame seeds to coat.
  3. Heat the oil in a non-stick skillet over high heat.
  4. Once the oil is hot, place the tuna steaks in the skillet.
  5. Sear each side for 1-2 minutes for a rare center. For medium-rare, sear 2-3 minutes per side.
  6. Remove from heat and let rest for a couple of minutes.
  7. Slice thinly and serve with soy sauce, wasabi, and pickled ginger.

Bigeye Tuna Poke Bowl


  • Fresh Bigeye tuna, diced into 1/2 inch cubes
  • 1/4 cup soy sauce
  • 1 tsp toasted sesame oil
  • 1 tsp rice vinegar
  • 1 tsp honey or sugar
  • 2 green onions, thinly sliced
  • 1 tbsp toasted sesame seeds
  • 1 avocado, diced
  • Cooked sushi rice
  • Optional: diced mango, edamame, cucumber slices, seaweed, and other preferred toppings


  1. In a mixing bowl, combine soy sauce, sesame oil, rice vinegar, honey, and mix well.
  2. Add in the diced tuna, green onions, and sesame seeds. Stir until the tuna is well coated with the sauce.
  3. Let the mixture marinate in the refrigerator for at least 30 minutes.
  4. Serve atop cooked sushi rice and garnish with avocado, and other desired toppings.

Grilled Bigeye Tuna


  • Fresh Bigeye tuna steaks
  • Olive oil
  • Salt and freshly ground black pepper
  • Lemon wedges and fresh herbs (like parsley or cilantro) for serving


  1. Preheat the grill to high heat.
  2. Lightly brush the tuna steaks with olive oil on both sides.
  3. Season both sides with salt and pepper.
  4. Place the tuna steaks on the grill and cook for 2-3 minutes on each side for medium-rare.
  5. Remove from the grill and let it rest for a few minutes.
  6. Serve with lemon wedges and freshly chopped herbs.

Remember, Bigeye tuna is best enjoyed when cooked minimally to preserve its flavor and texture. Whether you prefer it seared, raw, or grilled, this versatile fish offers a delectable experience for the palate


Bigeye tuna, with its unique adaptations and ecological significance, stands as a testament to the marvels of marine life. However, the balance between its commercial demand and conservation is a delicate one. A comprehensive understanding of its biology, paired with sustainable management practices, is vital to ensuring that future generations can both benefit from and admire this remarkable species.

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