In terms of bio load etc. a 10" big fish = how many 1" small fishes?

too many variables to give a definitive answer

Think about it in girth, 1 10" oscar may be 10 neons in length and 4 neons wide so think about how many would fit In it to get a better idea. But it still isnt an exact measurement probably just a better way to think about it

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What kind of diet does the bigger fish eat? How about the smaller fish? What about body shape, are they similarly shaped or is one fish stout while the other trim and flat? Are they diurnal or nocturnal? Are we comparing bottom dwellers to other bottom dwellers or are we comparing them to top dwellers? Are the fish all active species (or similar metabolism / activity level)? Are your water parameters and tank set-up ideal for both the big fish and the little fish or is it ideal for one, but maybe slightly sub-optimal for the other?

Those are some of the questions to consider before attempting to come up with an answer for a comparison like this. That's why any rule of thumb on this topic is going to be about as accurate as the watts per gallon rule for lights (which is only accurate for a very specific set of circumstances).

That being said.....

At a 1 to 10 ratio of "size", I really can't think of any situations where there'd be less than a 3:1 conversion (i.e. 3 small fish with similar bio load to 1 large fish). So 3:1, while perhaps a conservative estimate, is the highest I'd go with, particularly if keeping our fish healthy and not stressing the biological filtration are the top priorities. Besides, in most cases, you can just start with replacing 1 big fish with 3 smaller ones, and then later on if you're certain the tank can handle it, add one or two more at a time.

Yes, I put "size" in quotes. Mostly to emphasize that I'm not considering size solely as body length, but more in terms of volume and/or mass.

Would need to consider how active each fish is and how much mass it has to sustain. Both of those things will help to determine how much intake they require and how much output they create. Although I'm sure there are many other factors to account for. Such as, but not limited to, the type of diet needed and the efficiency of their digestion process.

EDIT: +1 digitalphrage. He ninja'd me, but said it much better.


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sevurms/discus have a slim body.
oscars/red devils have a thick body.

so yes it does matter on what you mean by a 10 inch fish.. is the fish thick or slim? tall or short? what does it eat? how often?

The 10" fish would be exponentially worse in terms of bio load...think about it. 10x 1" fish all produce very low amounts while a huge fish, oscar per say, will have one massive and ungodly bio load.

:cheers: