Inches per gallon and grams per kilogram? How much food?

There are quite a few places here where specific questions get asked about what food, how much, live vs frozen vs flake/pallet etc...I'm wondering if anyone discusses metabolic needs and reached some advice on how much food (Maybe grams) for how much fish (perhaps kilograms) - like the inches per gallon rules.

Now - I know it's more nuanced than that and the inches per gallon rule is roundly chastised here but for those needing simple advice and who have limited understanding such a rule is a helpful start.

Nor do I expect food is simple - there will be many variables: some foods are more nutritious or dense, metabolic rate is linked to tank temperature, age and growth stage of fish etc.but I'm sure some type of simple formulation would help e.g. 10g/kgfish/day halved if it's dry food ... (I'm sure that's not the rule but it's an example of how one might express it.)

In Alejandro's fish room I've calculated we go through about 1kg of food each week - we use only live and frozen almost never dry (we have a half full 250g can of dry crumble that has lasted 6 months so that looks like 5g dry food and 1kg wet food weekly) my estimate is he has about 12kg of fish living in his tanks.

It also varies from fish to fish - we use worms, maggots, crickets, brine, daphnia, prawn, fish, squid, shellfish all sometimes live, sometimes frozen. I'm sure I've forgotten some. (Oh yes soft shell crabs for his octopus)

So - how would you address food rationing in a way that could be easily used by others even if it's not perfect ?

Oh and thinking about it would the inch per gallon rule be better expressed in grams of fish per gallon as that relates better to waste output than inches.

 

Well, the old method of feeding only as much that is eaten in two minutes is the best I could come up with. I know it isn’t perfect but not a bad guide. Most people probably over feed vs under feed. Not sure about your weight method.

 

I don’t really use a method. Over time you figure out how much food is good for your fish and just feed them that amount. Yeah kinda lame I know.

 

So - how would you address food rationing in a way that could be easily used by others even if it's not perfect ?

You would have to go by the species, number of individuals per species and some other factors for each tank. There is material available online only for food calculation for professional zookeepers/animal handlers. I would look into that. Can't help there much though, as I saw that only once when a friend did their apprenticeship at a Zoo here in Germany.

Oh and thinking about it would the inch per gallon rule be better expressed in grams of fish per gallon as that relates better to waste output than inches.

The rules are all outdated and are so for a reason. As with the amounts of food needed, it all depends on the species and that species' lifestyle and main food sources. It can even depend on temperature. Higher temperature raises the metabolism in animals that can't keep their body temperature themselves (like invertebrates, fish, amphibians and reptiles).
Depending on how much and what they are fed a school of 20 cardinal tetras can have a smaller, same-sized or bigger bioload footprint than a bristlenose pleco.
Someone here on the forum said quite correctly: For a neon tetra just to keep sustained and hold their weight technically ONE FLAKE of standard sized flakefood per day is enough. Technically. As said above there are other factors.

So as you see, there are a lot of factors to be kept in mind.

And just a well meant advise: For money reasons alone, cut down on live and frozen foods and feed more dry foods. You will especially find it lowering the costs for water, as lots of live and frozen foods means more waterchanges.

 

And just a well meant advise: For money reasons alone, cut down on live and frozen foods and feed more dry foods. You will especially find it lowering the costs for water, as lots of live and frozen foods means more waterchanges.

Interesting - I would have thought the opposite that high nutrient dry food would add more waste than live or frozen and that that would lead to water changes needing to be more frequent. Do you have an explanation for how live/frozen creates more waste? I know "juice" from frozen is a issue but we usually melt and strain it - but other than juice not being eaten how would eaten frozen vs eaten dry make a difference if it was of equal nutritional value.

 

Even defrosted and strained frozen food contains a lot of fine debris that still gets into the water and is not eaten. With pellets and granulates you can feed more targeted and portion easier.
When you feed frozen food, there are some pieces the fish miss that fall to the ground and are thus not eaten and that many animals won't touch once they are on the ground for a quite short amount of time. Much is also simply ripped apart and distributed in the water column. The messier the fishes eating behaviour the worse that can get.

Another thing: Do I see that right? You feed daily?

 

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Another thing: Do I see that right? You feed daily?

Yes we try to feed daily but we sometimes miss one so maybe if say 6x weekly. Some feeds are lighter than others and some fish are fed less often

E.g. baby fish, seahorses, mixed tanks we try to do daily. Smaller predatory fish, and fast growing octopus, cuttlefish about twice a week. Bigger adult size predator like stargazer and anglers every 7-10 days.

I use growth to tell me what's good (Maybe not the best way??) But if it's not adult size and not growing I consider it underfed.

I get your point on waste but I try to get lots of frozen food cut to bite sizes so there's less mess - still some but for example if I cut frozen anchovies into 1cm pieces for Alejandro's reef they get pretty much all eaten- and he has species that will find left overs. We tried a prepared frozen food they called reef riot and it was a complete mess - like pouring a smoothie into the tank - disgusted with that we went back to preparing our own. So may be we are getting it close to ok and not too much waste - but it does concern me i'd prefer to be as close to accurate as possible even if only to save some money on saltwater changes (which can get expensive - he uses nearly 1000L of saltwater to do changes)

 

Ok, some things are hard to avoid.

Sounds like a bigger operation you're running there.
The variety of species seems to be your biggest problem besides age groups to find any kind of regularity. And I honestly doubt that there is one.
I would get into contact with a public aquarium, there are few and far between hobbyists that reach your dimensions.

 

Ok, some things are hard to avoid.

Sounds like a bigger operation you're running there.
The variety of species seems to be your biggest problem besides age groups to find any kind of regularity. And I honestly doubt that there is one.
I would get into contact with a public aquarium, there are few and far between hobbyists that reach your dimensions.

Thanks we do have communication with others - I'm a professional frog biologist and zookeeper but the fish are my 8 year old son's project. Some of my skills have transferred to help his fish passion but this forum.has been good and we've learnt lots. I'm ok with what we are doing with food but I'm keen to see what others do and how they decide as it helps generate other ideas. Its interesting that my way of solving problems (from my frog background ) is often different but then I see how fish people do it and find out that something in between is best so I'm learning and innovating from another specialty.

We are all learning all the time - I feel like when you stop learning life's over...

 

Ah, I see. I started with fish at that age, my dad and I ran a fishroom (freshwater, breeding setup for rift lake cichlids) for about 10 years. Due to most fish being wild caught we faced similar problems. But freshwater is a bit more forgiving in my opinion. Especially cichlids.