This is a model of a trigger fish rendered in Meccano.

A video of this model in motion is available.

The pectoral fins and the tail are fully articulated being powered by an axle that runs vertically down the middle of the army Multikit gun barrel. To meet the entry requirements for this challenge, it is necessary to replace the gun barrel with a shorter plastic Meccano axle -- ideally one of the later blue ones. The dorsal fin is immobile.

The internal mechanisms fit entirely inside the width of a U section curved plate -- that is a tad under 1" of width to work in. This means it is very tight and there are many fine tolerances and finger squeezes closing the assembly up.

Thanks are due to Graham Jost for assisting with the brainstorming of the tail mechanism, to Jack Parsisson who assisted with some of the parts and to Ian Sellick who designed the original model which was featured in a small photograph in the January 1978 Meccano Magazine.

There are additional photographs of the insides of this fish in my gallery.