FISH SCALES.

Ashburton Guardian, Volume 58, Issue 298, 28 September 1938, Page 3

FISH SCALES.

STORY OF THEIR DEVELOPMENT “The fish is a vertebrate,” says Air Brian Curtis in liis book, “The Life Story of the Fish.” “This means that he belongs to that great group of creatures which have backbones. An animal with a backbone does not seem strange to us today. But at the time that the first fish appeared upon earth, which we know from geological records to have been roughly five hundred million years ago, he must have seemed a miraculous thing. He was the very latest model iu animal forms, a radical, one might almost, say a reckless experiment of that force which we find it convenient to personify as Mother Nature.

“For up to that time no creature had over been made with the hard parts inside, instead of outside. There had been animals with little or no hard parts at all, like the anoeba, the seaanemone, and the jellyfish. And there had been animals with the hard parts outside, where they served as defensive armour and as framework for the muscles, like the starfish and the clam and the crab. “AVe can trace the development ol these lower forms, called invertehrales, and we can trace the development of the vertebrates from fish through amphibian through reptile to bird and mammal. But between invertebrate and vertebrate there is no connecting link. Nature might be said to have bad a brain-storm, abandoned all the earlier methods, and turned out overnight something absolutely new and unheard of.

“Only one feature did she carry over from the old models. She didn’t trust this new experiment of hers among her hard-shelled veterans and so she gave it a certain amount of external armoui ,

:is well as the new inner hard parts, to protect it from the old-timers.” After developing this theme, Mr Curtis, in a chapter entitled “Body Covering” says: “The tree, as we have all been taught, adds only one ring each year, and it is by counting the total number of rings that the tree’s age can be told. Each iisli-scale adds many rings eacli year; and yet the character of this ring-growth varies with the seasons to such an extent that it is possible for a practised person to look at a salmon scale under a microscope and tell not only how old the fish, is, but also how many years it spent in the sea, and how many times it has spawned—even, if it has not spawned, to calculate how long it was at the end of each year oi its life. No other animal known to man carries about with it such a complete autobiography.

“The method by which this autobiography can be read was originated by .Johnson and Dahl, working separatelv in England and in Norway, at the turn of the century, and in the light of their findings, the whole thing seems as simple as Columbus’s egg. In summer, when the water is warm and food plentiful, the fish feeds actively and grows fast. “The scale, during this period, must also grow fast in order to keep on covering its portion of the fish, and the growth-rings of the scales are therefore far apart. In winter, on the other hand, food is scarce, and temperatures are so low that the fish has not much appetite. He feeds little and grows slowly, if at all. The scale grows slowly, if at all, the growth-rings are close together, and a dark band i.s formed, called the annual check'. Count the number of annual checks and you have llm fish's age.”