I used to think what a fish eats was just trivia. Then I found out sardines eat almost nothing but plankton their entire lives, and it explained a lot about why they're one of the best things you can pull out of a can.
What Sardines Actually Eat
Sardines aren't picky so much as they're stuck near the bottom of the menu. What sardines eat comes down mostly to zooplankton, tiny drifting animals like copepods and crab larvae, plus a fair amount of phytoplankton when zooplankton is scarce. Ask whether sardines eat algae and the answer is yes, more or less. Phytoplankton is algae, just too small to see.
The Short List
- Zooplankton, mainly copepods and crab larvae
- Phytoplankton (technically algae, just microscopic)
- Krill, when they can find it
- Stray fish eggs
No hunting, no chasing, just swimming through open water with their mouths open and filtering out whatever's small enough to catch. Not a glamorous way to eat, but it works.
What Type of Fish Is a Sardine, Actually?
Here's where it gets confusing. Sardine isn't one species, it's a name applied to about 21 different small, oily fish in the herring family, depending on where you're standing when you ask. Buy a tin labeled pilchard in Europe and you're often getting the exact same fish sold as sardine somewhere else, just at a different size or age. Same fish, different name tag.
What Eats Sardines, and Why That's the Part That Matters
If you want to know what fish eat sardines, the list is long, and none of it is flattering.
Sardine Predators, Ranked by Whether You'd Want to Meet One
- Mackerel – picks them off in open water, one of the most common predators around
- Hake – hunts them from below, patient and relentless
- Bluefin tuna – can outswim almost anything in the ocean and treats a school of sardines like a drive-through
- Seabirds – dive-bomb schools from above whenever they surface
- Loggerhead turtles – slower, but happy to pick off the stragglers
- Predatory jellyfish – get in early, snagging sardine eggs and larvae before they're big enough to swim away
What animals eat sardines really just comes down to anything bigger than a sardine and hungry enough to try, and in the open ocean, that's most things.
That's where the diet loops back around and actually matters. Sardines sit low on the food chain because their diet sits low on the food chain. Plankton eaters don't accumulate the mercury and heavy metals that build up in fish that spend their lives eating other fish. A bluefin tuna eats sardines, which ate zooplankton, which ate phytoplankton. By the time you get up to the tuna, whatever was in the water has been concentrated several times over. A sardine skips almost all of that, which is a big part of why it's near the bottom of every "fish to actually eat" list and tuna is stuck worrying about portion sizes.
Where Sardines Actually Live
Before any of that, sardines spend their lives in cool, nutrient-rich coastal water, the kind that's thick with the plankton blooms they depend on. Where sardines live tracks pretty closely with where their food is. You'll find them off the coasts of Portugal, Spain, Morocco, and California, anywhere cold currents stir up nutrients from deeper water and feed the plankton at the surface. They travel in dense schools, partly for safety in numbers against that long list of predators, and partly because the same currents that concentrate their food also happen to concentrate the fish eating it.
That's also why sardine season and sardine quality shift by region and time of year. When the plankton bloom is heavy, the fish feeding on it are fatter and more flavorful, which is part of why a tin canned at the right moment tastes noticeably better than one packed off-season. Federal fisheries scientists actually track these population swings year to year, since a bad plankton year for sardines ripples up through everything that eats them.
What's Actually in the Can: Nutrition, by the Numbers
All that plankton-eating adds up to more than just clean fish. It's also a genuinely dense nutrition profile, and the numbers back it up better than any "superfood" label could.
Per Can (3.75 oz / 92g, Drained)
| Nutrient | Amount | % Daily Value |
|---|---|---|
| Calories | 190 | — |
| Protein | 23g | 46% |
| Omega-3 (EPA + DHA) | 0.9g | no established DV |
| Calcium | 350mg | 27% |
| Vitamin D | 4.4mcg | 22% |
| Vitamin B12 | 8.2mcg | 342% |
| Selenium | 48mcg | 88% |
Source: the federal government's own nutrient database, for Atlantic sardines canned in oil, drained solids with bone (FDC ID 175139). This is a nutrition highlight reel, not the full label, focused on the numbers that make the case for eating them.
Why the Bones Matter
Those soft little bones you can feel if you chew slowly aren't a flaw in the canning process, they're most of that calcium. Skip them and you're leaving a real chunk of the nutrition on the plate. The canning process softens them enough that most people never notice, which is the whole point.
Sourcing and Sustainability: Why the Label Matters as Much as the Fish
Sardines are one of the rare seafood choices where eating them responsibly and eating them well point in the same direction. They reproduce fast, mature early, and don't take long to bounce back from a heavy fishing season, which makes them a lot more forgiving than slow-growing fish like tuna or cod.
What to Look For on the Tin
- Catch date or "packed on" date – fresher catch means better flavor, not just better ethics
- Country of origin – Portugal, Spain, and Morocco all have long-established sardine fisheries worth knowing by name
- Certification marks, like the seal nonprofits use to vet responsible fisheries, when present
- Catch method, if listed. Purse seine is standard for schooling fish like sardines and is generally considered low-impact for this species
Why Small Fisheries Matter
Smaller, regional fisheries tend to can closer to the catch, which is where that fresher taste actually comes from. It's also where the sustainability case is easiest to verify, since the boat, the water, and the tin are all a lot closer together than they are with mass-market seafood.
So What Does This Mean for the Can in Your Pantry?
It means the boring diet of a small, unglamorous fish is basically the reason it ends up being one of the least contaminated things you can eat from the ocean, and the numbers on the label back up what the food chain already told you. Sardines eat plankton their whole lives and not much else. That one fact is doing more work for your health than most of what gets marketed as a superfood.
Next time someone asks what do sardines eat, you've got a better answer than "plankton or something." You've got the whole reason the tin is worth opening in the first place.