Gentle, precise, fast, and simple method to measure the volume and mass of octopuses without the need to take them out of their tank

Presenting Author: Wolfgang Slany

Author: Wolfgang Slany

Graz University of Technology, Austria.

The Slany method 😉 allows routinely measuring the volume and mass of octopuses with high precision without taking them out of their tank. It does not require any special handling or immobilization of octopuses, besides common husbandry practices such as feeding. The method thus is particularly well suited to gently handle animals without harming them physically or emotionally, in fact it is rewarding and enjoyable for the octopuses. It can be carried out without the need for any special equipment. A sufficiently large bin is immersed into the tank. The border of the bin is higher than the water level in the tank. The bin can be transparent or opaque. Tank water is inserted into the bin up to a level that leaves enough space in the bin so that the octopus, once inside the bin, does not make the bin spill over. The octopus is shown that a crab has been inserted into the bin. The octopus will, attracted by the prey, go over the border of the bin and enter it. The difference between the water level in the bin before the octopus enters it and after it entered corresponds exactly to the octopus’s volume, and can be easily measured with a builtin scale or similar methods. Mass is then computed by multiplying with the known density of octopuses (depending on species, but mostly they have neutral buoyancy). The border of the bin can be more or less high depending on the species and to allow getting rid of water.

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