It is not just a yellowfin. Look at a bigeye tuna and you might think you are seeing a yellowfin that has been hitting the weights. It is larger and more robust. The deep, powerful body speaks of strength rather than just speed. The back is dark metallic blue. The belly is silvery. The fins are a pale yellowish colour. They are less flashy than its cousin. The pectoral fins reach almost to the anal fin. But the giveaway is in the name. The eyes are huge. They are adapted for straining light in the dim depths where this fish spends its days. Vision defines the niche. While other tunas patrol the surface, the bigeye goes down. Way down. Two hundred to three hundred metres deep. Into cold, dark water where the pressure would make most fish uncomfortable. It feeds on squid, fish and crustaceans in that sunless realm. It follows the vertical migration of prey that rises at night and sinks at dawn. At night it follows the food up to the surface. This is when anglers occasionally catch one while trolling or drifting. Built for endurance rather than outright sprinting, the bigeye can sustain deep dives that would exhaust a yellowfin. The stamina is exceptional. The depth is routine. Here is the thing about bigeye tuna in New Zealand waters. Most anglers cannot tell them apart from yellowfin. They get misidentified. Released or kept without a second thought. But the bigeye is different. The flesh is fattier. Richer. More valuable. Especially in the Japanese market where it commands premium prices. To catch a bigeye is to land the mystery tuna. The one that looks familiar but fights from a different depth. A deep, dark, delicious secret of the blue water. The value is hidden. The distinction is subtle. The reward is financial. No widely recorded Māori name exists for this fish. It lives too far offshore to have entered traditional coastal knowledge. The distance creates the gap. The depth ensures the silence. Today it is the fish of the deep set. The one that takes your bait 200 metres down. And leaves you wondering until it breaks the surface. The anticipation is prolonged. The identification is delayed. The catch is significant. It carries on in the deep. Unseen by the casual observer. But prized by those who know. It remains in the blue. A testament to the intact ocean. A relic of the wild deep. It waits for the line. Or it does not. The choice is random. The outcome is certain. The fish persists. It moves through the water. Unaware of the market. Unconcerned with the price. Focused on survival. And the next meal. In the cold, dark expanse. Where it belongs. The bigeye endures. No one told it otherwise.