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What Do Saltwater Fish Eat? Should You Give Them Flakes?

What Do Saltwater Fish Eat? Should You Give Them Flakes?

The first time I bought a pair of damselfish, I was overwhelmed with the myriad of food choices I could offer them. I mainly relied on standard flakes and pellets for my freshwater fish as a staple diet and occasionally treated them with frozen food. 

So, I was dumbfounded when my damselfish avoided probiotics-enriched flake food I had lovingly bought for them. 

As it turns out, most saltwater fish are finicky about what they put in their mouth. This is even truer for wild-caught specimens who are forced to change their diet from live and meaty snacks to processed food overnight. 

If you’re wondering what do saltwater fish eat, you have come to the right place. This blog will not just shine a light on the food choices we have to offer but also touch on the right feeding practices. 

Let’s begin without further ado! 

What Do Saltwater Fish Eat? 

Saltwater fish are of three types: herbivores, carnivores, and omnivores. Herbivores primarily snack on algae and flowering seagrasses. They consume both microalgae and macroalgae. Carnivore fish eat each other. It’s all about ‘eat or get eaten.’ They also consume shrimps, plankton, and crustaceans. Finally, omnivores enjoy pretty much everything under the sun. 

If you look at the content of commercially available saltwater fish food, you’ll notice that they basically come in three standard formulas: those primarily based on algae, those made with shrimp, squid, krill, shrimp, and fish, and lastly, a combination of first two. 

Towards the end of this article, I’ll give you a few product recommendations based on what I like and don’t like. But before that, let’s have a closer look at different food options we can offer saltwater fish. 

Live Foods 

If your fish could talk, they’d tell you they’d love to have live food all the time. Marine fish love live food. As long as it’s moving and meaty, they won’t be picky about what they eat. 

Some live food options your fish will love are:

  • Brine shrimp 
  • Mysis shrimp 
  • Feeder fish 
  • Blood worms 
  • Earthworms
  • Black worms 
  • Sludge worms 
  • Copepod 
  • Plankton 

Live food especially comes in handy to encourage fish to spawn. My favorite live foods to give them are blackworms, brine shrimp, and earthworms. 

Black worms are loaded with calories. So, I’d recommend giving these only sparingly. 

Adult brine shrimps aren’t as nutritious. Therefore, you should enrich them with selcon to make them healthy. Thanks to their rhythmic pulsing and swimming movement, fish go gaga over them. 

Earthworms can easily be found in the garden if you are willing to look for them. However, wash it clearly first, so there’s no trace of dirt. 

The most critical step when feeding your fish live food is to procure them from a reliable source. You don’t want to provide anything that has been raised in congested, murky environments. They can potentially carry life-threatening diseases (at least for your fish).

Frozen Foods 

Most foods available as live foods are also available in frozen form. So you can buy anything literally, from krill and bloodworms to cockle, mussels, and red plankton.

But my go-to choice would be mysis shrimp. 

I’ve given my fish frozen bloodworms, brine shrimp, plankton diet, and angelfish diet, but in my experience, no frozen food is ever eaten as greedily as mysis shrimp. 

My fish just love it. 

I alternate between buying cubes and sheets for no apparent reason. The sheets definitely offer more value for money, but you’d be trading convenience. Busting up the sheets can be pretty tricky. 

All in all, frozen foods are loaded with essential nutrients and are a lot easier to prepare than live food. As a matter of fact, certain saltwater fish only prefer frozen/live food and won’t even bother tasting flakes and pellets. 

Frozen food should ideally make up a major portion of your saltwater fish diet. And remember, variety is the key. Just because they enjoy a particular frozen food doesn’t mean you should only give it all the time. 

Lastly, be careful not to overfeed frozen (or live) squid. It’s exceptionally fatty. 

How To Feed Fish Frozen Food?

I defrost the food first in RODI water, so it is decontaminated. I then strain it, break it into smaller pieces and feed my fish. I use a plastic sieve and a small container to strain it. 

I also always keep a bottle of RODI water handy. 

You must thaw the food first. Otherwise, you’d risk fouling the tank. 


Pellets are part of the staple diet for most freshwater fish. But it’s not the case for marine fish. Therefore, processed food like pellets should only be given occasionally in moderate amounts. 

I don’t give my marine fish pellets often. However, if I have to, I stick to Hikari’s micro pellets. 

Remember to steer away from the floating variety when buying pellets since most marine fish are not surface feeders. 

Dried food like pellets become stale and lose their nutritional value quickly if not stored properly. Therefore, you need to keep them in an air-tight container, away from heat and light. 

I’ll tell you about the pros and cons of giving your fish pellets. And you can decide if it’s right up your alley or not. 

Pellets are nutrient-dense. Each small pellet is packed with essential nutrients. 

However, with saltwater fish, pellets are a hit-or-miss food. Your fish will either love them or hate them. If your fish love pellets, they’ll go after them the millisecond they drop into the water. 

If not, you will have soggy pellets lying all over the floor. And you just bought yourself some extra cleanup time! 


No other food comes on top of flakes when it comes to convenience. What’s good about flake food is that they require zero prep or handling. And they kinda last forever, don’t they? 

On busy nights, I just grab a tiny pinch and swirl it into the water. 

Judging based on parameters like price, conveniences, and the excitement with which my fish consume it, I’d recommend getting Spirulina Flakes from ZooMed. 

However, take my advice with a pinch of salt because not all saltwater fish love flakes. If left uneaten for too long, the flakes will give rise to algae problems. 

Freeze-Dried Foods

Freeze-dried foods make excellent supplements to saltwater fish diets since they are enriched with vitamins, minerals, and a good protein concentration. 

You can get all kinds of freeze-dried food for your fish. But the most popular ones in the hobby are brine shrimp, mysis shrimp, daphnia, plankton, krill, tubifex, and bloodworms. 

Freeze-dried food is naturally more convenient than live and fresh food since it has a much longer shelf life. But do you know freeze-drying food also helps with vitamin conservation?

Thanks to its texture, freeze-dried food can be crumbled or broken up into smaller pieces depending on the fish’s size, making it a low-waste, cost-effective option. 

I’d recommend stocking up on different kinds of freeze-dried food so that your fish can enjoy a varied diet that is rich in nutrition throughout the week. 

Here’s a link to freeze-dried mysis shrimp by San Francisco Bay Brand that my fish love. 


If you have herbivore and omnivore fish in the tank, they’d love to graze on seaweed. 

If you’re introducing seaweed sheets in the tank for the first time, your fish may initially be afraid. 

And I wouldn’t blame them – they’re not used to seeing something big and strange hovering over them. So it may take some time for them to perceive it as food. 

Algae-eaters, herbivores, and omnivores love seaweed, like tangs, angelfish, wrasse, parrotfish, and surgeonfish. 

When feeding seaweed, one thing to keep in mind is that it can contribute to phosphate buildup in the tank. 

Therefore, before you start using it, make sure to run a test on the aquarium water to check if the phosphate level is under control. Then, don’t forget to perform tests routinely for a while after you begin feeding seaweed to see if it is contributing to phosphate buildup in the tank. 

Here’s a quick link to Ocean Nutrition’s Green Marine Algae Sheets that I recently purchased for my angelfish. 

How To Know If You’re Overfeeding Fish?

If you find food resting on the bottom long after the feeding time is over and nobody seems interested in it anymore, it’s a telltale sign that you’re overfeeding your fish. 

So, these are the signs that you’re giving your fish too much than what they require:

  • Frequent sighting of leftover food in the tank 
  • Food getting caught in the filter 
  • Food floating or blowing around the tank 
  • Spikes in tank’s ammonia, nitrate, and nitrite levels 
  • A foul smell reeking from the tank 
  • Cloudy water 

If you’re encountering any of these problems, remove the uneaten food swiftly, perform a partial water change, and feed less from the next time onwards. 

And that takes us to our next question! 

How Often Should I Feed My Saltwater Fish?

If you have a herbivore saltwater fish, it should have a constant food source (algae) available in the tank. Omnivores and carnivores can be fed moderate-sized meals twice a day. 

Truth be told, there’s no rule etched in stone to decide how often or how much to feed your fish. If you ask around, the answer will differ from one hobbyist to another. 

Keep on experimenting until you crack it – if you’ve got it right, you’ll know – the water quality should be excellent, and the fish should look happy and healthy. 

Frequently Asked Questions 

What Do Large Fish Eat In The Ocean? 

If the large fish in question is a carnivore, it will eat other fish, mollusks, crustaceans, squid, and octopus. If it’s a herbivore, it will snack continuously on algae, seagrass, seaweed, and phytoplankton. 

What Do Small Fish Eat In The Ocean?

Small carnivore fish eat smaller fish, fish eggs, crustaceans, and copepods. On the other hand, a small herbivore fish will eat seaweed, seagrass, algae, and phytoplankton. 

Final Words!

What do saltwater fish eat? Saltwater fish are of three types – herbivores, carnivores, and omnivores. So what they eat depends on their dietary needs. 

They can eat frozen, freeze-dried, and live food like mysis shrimp, blood worms, brine shrimp, blackworms, copepods, crustaceans, algae, seagrass, seaweed, and so much more! 

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