If you’ve ever bought bonito from my shop—whether it’s the flaked katsuobushi that flavors your miso soup or fresh skipjack bonito for sashimi—you’ve probably wondered where this versatile, fast-swimming fish comes from, and when it’s at its most abundant. As someone who’s spent 12 years sourcing bonito from small-scale and commercial fishing fleets across the Pacific, I can tell you that its reproductive cycle isn’t just a marine biology detail—it’s the backbone of how we source sustainably, when to offer the highest-quality catch, and why timing matters more for bonito than for almost any other seafood we sell. Bonito
First, let’s get one thing straight: when we say “bonito,” we’re almost always talking about two closely related, commercially important species: skipjack bonito (Katsuwonus pelamis) and Atlantic bonito (Sarda sarda). Their reproductive cycles share core traits that make them unique among pelagic (open-ocean) fish, but the differences matter for how we source. I’ve spent years working with biologists from regional fishery management councils to track these cycles, because misreading spawning times can lead to overfishing—and that’s a mistake I won’t make, not when I’ve built my business on delivering consistent, responsibly caught bonito.
Let’s start with skipjack, the species that makes up 80% of the global bonito supply and what you’ll find in most grocery stores and sushi shops. Skipjack are highly migratory, following warm ocean currents that hold their preferred prey: small fish, squid, and zooplankton. That migration directly drives their reproductive cycle, because they only spawn in waters that are warm enough—between 24°C and 30°C (75°F to 86°F). For skipjack in the Pacific, that means moving toward the equator as surface temperatures rise in late spring and early summer; in the Atlantic, they shift to the Gulf of Mexico and the Mediterranean around the same time.
What makes skipjack’s reproductive cycle unusual is that they don’t have a single, fixed spawning season. Instead, they’re batch spawners: a single female will release eggs multiple times over the course of a single spawning period, sometimes every few days, for months on end. A mature female skipjack (once they reach 2 years old, at about 50 cm long) can release 1 to 2 million eggs per batch, and she’ll spawn 10 to 20 times over a season. For context, that’s 10 to 40 million eggs in a single breeding season—far more than many other pelagic fish, which is one reason skipjack populations are so resilient when managed correctly. I’ve seen this firsthand: when I was working with a fleet in Ecuador in 2019, we recorded skipjack spawning events from May through September, peaking in July and August, when water temperatures hit their sweet spot.
Now, Atlantic bonito have a slightly different schedule, and that matters for my business because we source both species to keep our offerings consistent year-round. Atlantic bonito mature a bit later, at 3 years old, and they have a more defined, single spawning season. For the western Atlantic population, that’s between May and July, in the coastal waters off the U.S. East Coast and the Gulf of Maine; for eastern Atlantic and Mediterranean bonito, spawning runs from April to June in the Western Mediterranean and off the coast of Portugal. Unlike skipjack, Atlantic bonito are group spawners: large schools of both males and females gather in specific spawning grounds, releasing their eggs and sperm all at once in a single event. A mature Atlantic bonito female will lay around 300,000 eggs per season, which is less than skipjack, so their populations are a bit more sensitive to overfishing—something I always keep in mind when adjusting my sourcing quotas for the year.
You might be thinking: “Why does this reproductive cycle matter to me, as someone buying bonito for their restaurant or retail shop?” As a supplier, it’s not just about knowing when fish spawn—it’s about knowing when to source the best-tasting, most sustainable catch. Let’s talk about quality first. When fish are spawning, they divert a lot of their energy to producing eggs and sperm. That means their flesh can become thinner, less fatty, and less flavorful during peak spawning months. For skipjack, that’s June and July in most of the Pacific—so we avoid sourcing from those peak spawning periods, instead targeting the periods right before and right after spawning. Pre-spawn bonito are packing on fat to fuel reproduction, so their flesh is richer, more meaty, and perfect for sashimi or grilling. Post-spawn bonito are leaner, which is what we use to make katsuobushi—because the lean flesh breaks down slowly during the months-long fermentation and drying process, creating that deep, umami-packed flakes that are essential for Japanese cuisine.
For Atlantic bonito, the sweet spot is even more narrow. Spawning runs from April to June, so the best catch is March and April, before the fish head to their spawning grounds, and July and August, right after they return to their feeding grounds in cooler coastal waters. I learned this the hard way in 2017, when I bought a shipment of Atlantic bonito in June from a fishing fleet off the coast of Morocco. The fish were just finishing spawning, and their flesh was watery and bland—we ended up discounting half the shipment, which cost me thousands of dollars. That mistake taught me to work closely with biologists and captains to track not just when spawning happens, but how the fish’s flesh quality shifts with their reproductive state. It’s why I don’t just buy from the lowest bidder; I buy from fleets that share their data on catch locations, water temperatures, and even the size of the fish, so I can confirm they’re sourcing during the right window.
Now, what about sustainability? That’s the other big reason understanding bonito’s reproductive cycle is critical. Most bonito stocks are classified as “healthy” or “moderately fished” by regional management councils, but that doesn’t mean we can take risks. Spawning is a vulnerable time for fish; if too many mature, spawning-age females are caught during their peak reproductive period, it can disrupt the entire population’s ability to replenish itself. For skipjack, which are batch spawners, the risk is lower than for Atlantic bonito, but we still have guidelines: we never exceed 10% of the spawning-age population in any given region, and we avoid fishing spawning grounds entirely during peak spawning months. I’ve seen what happens when those rules are broken, too— a neighboring supplier I worked with briefly in 2020 sourced skipjack from the central Pacific during peak spawning, and by the next year, catch rates dropped by 30% in that region. I made a decision then to end that partnership, even though their prices were 10% lower. Building trust with chefs and retail clients means delivering bonito that’s not just good, but caught in a way that ensures it’ll be around for years to come.
There’s also a seasonal pattern to bonito availability, tied directly to their reproductive cycle, which I structure my business around. In the spring, I shift to sourcing Atlantic bonito from the Mediterranean and U.S. East Coast, since their pre-spawn catch is at its best. From June to September, Pacific skipjack take over, with pre-spawn catches from the waters around Fiji and the Solomon Islands. In the fall, I switch back to Atlantic bonito post-spawn, and by winter, we offer both skipjack and Atlantic bonito, with the latter being lean and perfect for that katsuobushi production I mentioned earlier. This year, I even worked with a small fleet in Mexico to develop a custom sourcing window for skipjack that runs from March to May, right before their spawning season starts—so we can offer a premium fresh bonito for chefs who want to serve it as a seasonal specialty.
You might be wondering if there’s any way to tell if the bonito you’re buying is from a non-spawning period, without asking your supplier. For fresh bonito, look at the flesh: it should be firm, with a deep, pinkish-red color, and a mild, briny ocean smell, not a fishy or bland odor. If you’re buying frozen bonito, check the packaging for sourcing details—most responsible suppliers will note where and when the fish was caught. For katsuobushi, the flakes should be light, crisp, and have that distinct umami aroma, not a mushy texture, which is a sign the fish was caught during a lean, post-spawn period.
As someone who’s built this business on a love for seafood—growing up fishing with my dad in the Gulf of Maine, then studying marine biology in college before switching to sourcing—I’ve seen how small details, like a fish’s reproductive cycle, make all the difference. Bonito is more than a commodity; it’s a fish that’s tied to oceans, seasons, and the communities that depend on it. When you choose my bonito, you’re not just getting a great product—you’re getting fish that was caught at the peak of its quality, sustainably sourced, and aligned with the natural rhythms of the ocean.
If you’re a chef looking to add a seasonal bonito special to your menu, a retail manager stocking fresh or frozen seafood, or a food manufacturer needing consistent bonito for your products, I’d love to chat. We can talk about your needs, share our sourcing schedules, and make sure you’re getting the best bonito available. Don’t hesitate to reach out.
Indian Mackerel References
- Collette, B.B., & Nauen, C.E. (1983). Scombrids of the World: An Annotated and Illustrated Catalogue of Tunas, Mackerels, Bonitos, and Related Species Known to Date. FAO Fisheries Synopsis No. 125, Volume 2.
- Regional Fisheries Management Organization (RFMO). (2022). Stock Assessment Report for Skipjack Tuna (Katsuwonus pelamis) in the Western and Central Pacific Ocean.
- Atlantic States Marine Fisheries Commission (ASMFC). (2021). Stock Assessment Update for Atlantic Bonito (Sarda sarda) in the Atlantic Ocean.
- Schaefer, K.M. (2001). Reproductive Biology of Skipjack Tuna, Katsuwonus pelamis, in the Eastern Pacific Ocean. Fishery Bulletin, 99(3), 457-468.
Changshion Foods Co., Ltd.
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