Dried Anchovies 100g

Break one in half first. A whole fish runs 3 to 5cm, which is more food than a small colony will clear while it is still fresh, and the broken edge gives them a way in. Dried skin is tougher than it looks and an intact anchovy can sit for a day or two while the colony works around the outside of it.

What is in the bag is fish and nothing else. No binder, no colourant, no vitamin premix, no preservative. The animal with the water taken out of it.

The figure to look at is the ash

Ash on a feed label is what survives after everything organic has burned away, so it stands for the mineral content. These come in at 15.8%, and in a whole small fish most of that is skeleton. Protein is 70.4%, oils and fats 4.3%, fibre under 0.2% and moisture under 12%.

Read in that order it changes what the food is for. Plenty of things will deliver protein to an invertebrate colony. Far fewer deliver protein and calcium through the same door, and that is what a whole fish does.

Why calcium is worth targeting

Isopods reclaim what they can from their own cuticle at each moult, which is why you see them eating the shed halves. It is not enough on a substrate made of leaf and rotten wood, and a colony short of calcium moults badly and breeds slowly. Cuttlebone and crushed limestone are the standard fixes and I still keep both in every tub.

This sits alongside them, not instead of them. The difference is that a mineral block waits to be found, and a fish gets eaten with some urgency.

Portions, and knowing when to take it out

Half a fish suits an established tub. A quarter for a young culture or a small species. Armadillidium will cover one within a few hours if the colony is dense.

Fish spoils in a way plant food does not. In a warm humid box the flesh softens and starts to smell, and that is the point at which flies find it. My rule is simple: if a piece smells of anything at all, it has been in too long. Nothing should be sitting there on day three.

What else will take one

Millipedes want calcium more than almost anything else on their shelf and will work at a fragment steadily. Roaches and darkling larvae strip one fast. Springtails graze the surface without making much impression on it.

Keeping them

Sealed, dry and dark. The risk with a dried fish is not damp so much as the oil going rancid, and warmth and daylight are what drive that. A cupboard is fine. The bag should smell clean and faintly of the sea when you open it, and if it ever smells sharp instead, that batch has turned.