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Ask Dr Dazza | Squid

Posted: 3pm 14 Jul 2021

Last edition, I went through some of the features of the local tiger and pencil squid including how fast they grow and how short their life span is. This time, I’ll look at some of the other features of these fascinating animals.

Squid have a lot of heart. Three in fact. They have a systemic heart which pumps blood around the body and two hearts which pumps blood to each set of gills. Among the invertebrate animals, squid have the best developed nervous system.

Squid have eyes that are superficially like that of vertebrate animals such as mammals, however they differ in terms of how they focus and their ability to see polarised light. If you want to see how your squid jig looks to a squid, have a look at it while you are wearing a pair of polarised sunglasses.

As squid fishermen know, squid respond strongly to light. The light environment that squid best respond to differs between species. Our local squid species prefers a level of underwater light illuminance between 2.5-10.0 lux. The colour of the light is substantially less important. These are things to think about if you are looking at buying a light to attract squid.

Anyone who catches squid must deal with the ink. Squid eject the ink to distract predators. It creates a visual cloud in the water, and it may chemically deter some predators. However, its main function is it to create a cloud in the water that buys the squid a little bit more time to escape from a potential predator. The main chemical compound in squid ink is melanin which is also found in human skin. Squid ink is used in art, painting and cosmetics but is most used in Mediterranean and Japanese cooking. There is some medical interest in squid ink because of its anti-microbial and anti-inflammatory properties.

Squid have an internal skeleton called a pen which most anglers that catch them are familiar with. The pen is the evolutionary remnant of the typical mollusc shell. Octopus lack a pen or any internal skeleton. The pen is made of chitin – a modified polysaccharide.

Squid can change colour – both in the water and after you have caught them. They achieve this by using their chromatophores on their skin. These are pigment sacs which the squid can open and close individually. In the water they change their colour to blend in with their background and can also use colour changes as a means of communicating with other squid of the same species.

Next time you catch a squid, think about the wonderful adaptations the animal has!

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