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Scyliorhinus canicula – dog or cat…

6 April 2012

On Cromer beach this afternoon I found what I assumed was a dogfish, sadly dead, Scyliorhinus canicula, that had been washed up caught in a mass of  weed brought in on the high tide and in a strong onshore wind. Dogfish are a classic biology dissection animal, and are eaten as ‘rock salmon’. However it turns out to my mortification at my ignorance of pelagic fish, that the dogfish is Squalus acanthias. See here for a beautiful illustration from the 19th century  (with the closely related stellaris )-

This is a ‘catshark’.

There is a new article “Development of tyrosine hydroxylase-immunoreactive cell populations and fiber pathways in the brain of the dogfish Scyliorhinus canicula: New perspectives on the evolution of the vertebrate catecholaminergic system” which studied the development of neuron clusters that contain neurotransmitters in the brain. [The authors seem to use the term dogfish not catshark, which shows exactly why common names are so useless!] They are known as  Catecholaminergic cell groups. To decode the abstract you need to know a fair bit about brain development – what little I knew from reading pop science books on the brain, I have forgotten!

  • recall that gnathostomes are jawed vertebrates, so that includes us (assuming anyone who reads this is human)
  • Chondrichthyes are catillaginous fish – sharks – to which group the dogfish (aka catshark!) also belongs
  • Neuromery refers to “morphologically or molecularly defined transient segments of the early developing brain” (thanks Wikipedia)
  • Tyrosine hydroxylase (TH) is an enzyme involved in catalysing the conversion of an amino acid to the precursor of dopamine

During the brain development TH-immunoreactive (ir) cells grew in much of the brain –

When the second half of embryonic development started (S32), TH-ir fibers innervated most brain areas and nearly all TH-ir cell groups of the postembryonic brain were already established. This study provides key information about the evolution of the developmental patterns of central CA systems in fishes and thus may help in understanding how the vertebrate CA systems have evolve.

Here is the egg case from a photo I took in the wonderful Grant Museum –

Egg cases of chondrichthyes

Anyway, insubstantial as this post is, it has taken me a whole evening to write as I have had to do a lot of (enjoyable) digging that has taken me into fish and brains. No link there?

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