Backyard Aquaponics
A place to discuss aquaponics

Something has been puzzling me for a while. Floating fish food pellets come in a number of sizes from 3mm upwards, there doesn't seem to be a price difference.
I can think of a number of logical reasons for feeding the smaller size (gives the smaller fish more of a chance, I assume easier to digest) but none for feeding the larger sizes.
Obviously there must be a reason, but would anyone care to enlighten me.?

Small feeds are for small fish.

Big feeds are for big fish.

I think I must be missing your question

You normally feed by weight, so x weight of small pellets is the same as x weight of larger ones ie the fish are getting the same amount of feed. Smaller pellets provide a larger surface area for digestion (initially) and as I said the more pellets on the surface the better the chance that all the fish will get a similar feed.

I have to feed the smaller as I have a number of generations of goldfish in the same pond but I was just curious.

The theory is that by eating a larger pellet the fish will expend less energy (therefore put on more growth) than by eating many smaller pellets. Although prices for 3mm upwards are generally similar the prices for the very small stuff skyrockets.

That's an interesting theory Gavin, but the sizes are not that much greater and it does cost energy for digestion.

That is true but the energy is not expended in breaking up the pellet. Cows spend a bit of energy physically processing their food but the majority of energy of over coming the chemical bonds in the food to release the stored chemical energy.

With fish food pellets in the gut they essentially dissolve.

It depends on the fish but some fish have relatively small mouths and throats (trout for example).

Commercial feeds are produced in different sizes and blends to suit the life stage of the fish. Small fish foods often have higher protein and oil contents which helps to make them more expensive (not the only reason). The spec sheets on the various feeds let you know all this.

For backyarders it is often difficult to get feed in multiple sizes so we just feed the one pellet size. For a BYAP system it probably doesn't make much difference.

Ok thank you Stuart and Gavin.

Is it true that you should use a pellet size in relation to the size of the fish's eye?

I don't know. Some fish don't have eyes .

I think it would be more to do with their mouth and gut. Large Mouth Bass could eat a much larger pellet than a trout of the same length or weight.

smaller pellets, smaller poos to some extent. may have a bearing on ease of solids removal in backyard systems.

That sounds fishy to me....

If you want to come out to our farm and try feed 3mm pellets to our 10kg broodstock id be more than happy to pull up a chair for a laugh.

For trout it doesnt matter too much, we found some little 90gram trout in a broodstock pond recently that had been eating 10mm pellets, god knows how they fitted it down their throat.

For salmon they are heaps pickier, if they dont like the size they will spit it out quick smart.

We always try move them up feed sizes as quick as possible till 3mm for cost reasons but also for wastage reasons. If the feeder spits out 50g of food the salmon only have about 10-15 seconds to eat it all before it hits the bottom and is wasted, 2mm vs 3mm food would be like 30-40% reduction in number of pellets so more chance they will eat it all before its wasted. They also expend less energy chasing pellets.