# What do fish eat



## Paul B (Aug 4, 2009)

Just some of my observations:

Oddly enough fish in the sea do not eat flakes, bloodworms, mosquito larvae, mysis, brine shrimp, squid tentacles, fish fillets, or pellets.

They eat what they were designed to eat and they only live in the areas where those foods come from. If a fish is in the one or two percent that is lucky enough to actually makes it to adulthood it probably means that it has learned a couple of things, one is to evade predators and the other thing is to find the food that it needs every day and not just once a day.

Most fish eat a very little bit all of the daylight hours and the rest eat only at night. Having good eyesight is not as big a deal for a fish as it is for us. They get along quite well with just one eye or in total darkness and they have evolved to eat a certain type of food that it needs for its particular physiology.



A fish like a mandarin was built to take advantage of a food source that most other fish of that size will not even notice. But such an active fish as a mandarin needs a lot of food and just about all it can eat are pods and other creatures about the same size. Pods are invertebrates and therefore mostly shell with a little “pod meat” inside. Pod shells are mostly chitin like our fingernails and have almost no nutrition except for maybe some calcium. In this hobby we call any tiny creature a pod or copepod but in reality these creatures in our tanks and in the sea are mostly an assortment of tiny larvae of larger crustaceans such as crabs and shrimp but some are bonified copepods.



Other fish such as tangs live on fresh seaweed or algae. Algae grow on all healthy reefs but because of all the herbivores we usually don’t see it. Luckily for these animals it grows very fast but they had to develop jaws and teeth to take advantage of this paper thin quantity of food. As they graze on algae they also pick up any pods, worms, slugs or inverts that happen to also be grazing on the algae. This “by-catch” is important to the health of these fish as it supplies other nutrients that are missing in algae.



Fish with long snouts like Long Nose Butterflies and Copper band Butterflies evolved to take advantage of a food source that resides in holes in rocks. These snouts are a disadvantage to these fish when it comes to defense or swimming because their jaws are weak and fragile. Their teeth are very small to fit in such jaws and are only suited to eat small soft foods like worms and tiny shrimp.

These types of fish need a large part of their diet to be oily like worm flesh is and is one reason these fish do not live as long in captivity as many other fish.



Most other fish in the sea eat whole fish. If you do any diving in the tropics and you look closely near the bottom you will see multitudes of tiny fry. This is the main source of nutrition for many fish. All fish have a liver which serves two purposes. The main purpose is the same reason we have a liver, to cleanse our blood but the other reason is buoyancy. Oil is lighter than water and the oil in their liver allows the fish to be almost neutrally buoyant. Their swim bladder is used for more delicate adjustment of buoyancy but the liver is the main organ that keeps fish from sinking like a rock. Without a liver and swim bladder even us humans would be able to swim better than a fish because we have quite a lot of air spaces, fish do not.



This fish oil is also invaluable to a fishes health as fish do not have fat like mammals.

Being cold blooded animals a fish can not utilize fat because it would remain solid at the temperatures in a fishes. Out 98.6 degree temperature allows up to eat solid fats.

(But fish oil is also much better for us to eat in small quantities in stead of solid fats) 

Also when a fish spawns, almost all of that spawn is oil. Oil is what nourishes a new born fish until it is able to hunt on its own.

When a fish is in spawning condition it also has a super immune system as many animals in that condition have. It takes a large toll on a fish to produce eggs that could be a quarter of the fishes weight. Much of that weight is oil and most of it comes from eating whole fish. They can produce some of it on their own but it is much easier on the fish to be able to eat a diet high in oil.

If a fish eats another fish it gets about 25% of it’s meal in the form of pure fish oil just which is just what it needs to produce eggs and rev up it’s immune system.

Fish in spawning condition are “almost” immune to most diseases.

When a fish eats another fish it also gets calcium from the skeleton and all the vitamins and minerals in the correct proportion that a fish needs.

In the accompanying photo taken in the Caribbean you can see tiny fry to the left of the nurse shark. Those fry are all over the place and almost all of the fish take advantage of that easily acquired drive through fare.


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## phys (Feb 4, 2011)

nice read! thanks!


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## wayfarer (Feb 22, 2011)

This is a good guide for fish owners. You have given relevant information about fishes and what they eat. Most of the facts you presented are new to me. I thought all fishes eat flakes. Your observation are pretty cool, all in all.


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## wimpyreef (May 15, 2011)

that was an awesome post Paul. Really.

Its been raining a lot recently where i live, and im seeing worms on the ground everywhere i walk. wanted to know if they were safe to feed clownfish.


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## Paul B (Aug 4, 2009)

The worms you find are safe to feed to your fish if you are sure there is no insecticides or weed killers used where they were collected. Anemones and bubble corals love worms as do most fish and crabs. Very healthy also.


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## denson (Jun 5, 2012)

You are sharing very helpful information for the fish owners. This will really helpful for them.The food of the fish depends on the type of fish, they can be herbivores, carnivores, or scavengers. Fishes eat any types of food designed for them in a pet store. Some even eat certain veggies and fruits.


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## Paul B (Aug 4, 2009)

> Some even eat certain veggies and fruits


This is true, many fish eat bananas especially if they are first frozen. My moorish Idol always used to love it.


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## jmann124 (Aug 15, 2012)

Paul B said:


> The worms you find are safe to feed to your fish if you are sure there is no insecticides or weed killers used where they were collected. Anemones and bubble corals love worms as do most fish and crabs. Very healthy also.


So the same worms, that I would dig up to go fishing with, I can feed my SW fish? How would I go about preparing them?


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## navigator black (Jan 3, 2012)

I'm over from the bad neighbourhood (freshwater) - but this post goes in a good direction. I feed a lot of earthworms. I put them in newspaper to clear their guts, and then (this is hard) put them in a fridge or freezer till they go dormant and chop them up. It feels cruel, but the fish growth is great.
They are not good for herbivores whose guts are not evolved to deal with them, but for carnivores, they work well. I find most insects are readily eaten by carnivores and omnivores - mammal meat isn't for Paul's clearly stated reasons- too terrestrial. The fats don't go well. 
Every once in a while, in summer, I go nightcrawler hunting. And every time I work in my garden, my Geophagus are happy. 

You can go pdf hunting, something I suspect Paul B does. Search for your favourite fish via its Latin name and add pdf to the search. You can pull public domain scientific papers, many of which include stomach content analyses of wild caught specimens. It's invaluable for preparing a diet tailored to the niche the fish comes from. You'd be surprised how many ants fall in tropical freshwater streams... there must be similar detailed info for salt water.


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## Reefing Madness (Aug 12, 2011)

Welp I'm the bad apple here. Last time I checked, earth worms were not part of the SW fishes diet, meaning, how in the hell would they get an earth worm in the ocean?


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## coralbandit (Jul 29, 2012)

rivers flow to the ocean. the food chain also travels as water.marine life recieves what comes from rivers in some small way.I believe marine life could/would eat earth worms and that may be highly nutritous also. Now I don't think much fresh water life could eat marine life the same. The water doesn't flow that way.


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## jmann124 (Aug 15, 2012)

Reefing Madness said:


> Welp I'm the bad apple here. Last time I checked, earth worms were not part of the SW fishes diet, meaning, how in the hell would they get an earth worm in the ocean?


I was thinking the same thing. But if anyone can show me where or how earthworms are a good part of my SW fishes diets, I'm on board. It's cheap food.


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## Reefing Madness (Aug 12, 2011)

jmann124 said:


> I was thinking the same thing. But if anyone can show me where or how earthworms are a good part of my SW fishes diets, I'm on board. It's cheap food.


Yea right. I hear that.


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## Paul B (Aug 4, 2009)

Earthworms are a great food source for saltwater and freshwater fish. Earthworms are not freshwater animals, they are land animals. It doesn't matter if saltwater fish would ever find an earthworm in the sea. Humans can also eat squid and if you are a human living in Utah, how many wild squid would you find, but you can eat them.
Fish eat pellets and flakes, that is also not normal for them.



> You'd be surprised how many ants fall in tropical freshwater streams..


When I started in the fish keeping hobby in the fiftees, dried ants were sold as fish food. Thats about the only thing you could get to feed fish.
Worms are much better though.
Worms would be much better than any flakes or pellets you could buy.


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## navigator black (Jan 3, 2012)

I'm with Paul - earthworms are terrestrial, but they seem easily digested and to have nutrients all carnivorous fish love. To stretch the debate - if I feed ants to my West African killifish, I can guarantee you they are not the same species of ants found in Cameroon. So should I stop?
The diet we feed our fish is by its nature artificial. Unless you catch fish from your local streams, and feed them local bugs, it's always a stretch. 
For reef fishes, whatever we feed is just an honest attempt to approximate their rich diet in nature. And hey, I just stuck a chunk of good Bay of Fundy purple seaweed into a tank full of wild mollies from Michoacan Mexico, and they are happy as pigs in, ummm, what pigs sit in.


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