National Geographic : 1931 Mar
TROPICAL TOY FISHES desirable variations by careful cultivation of modified forms, the extent to which distribution of color and fin development are dependent upon agencies of tempera ture, environment, age, food, and other factors, and other biological features of the toy fish, commend themselves to the attention of the scientist, and in many a biological laboratory a collection of pyg mies forms an important part of the equipment. Lepidology, the study of the scales, in which the age of a fish is recorded, has not yet been applied to the pygmies to dis cover their natural term of life. PYGMIES AT BIRTH RESEMBLE TWO LARGE EYES As among larger fishes, the young hatched from eggs are transparent, very delicate, and unable to feed, the umbilical sac (yolk sac) supplying nutriment for a few days and also retarding their move ments. These require rich foods-live in fusoria, diatoms, Daphnia; also, the juices of meat and shellfish. But pygmies born alive are as fully formed as adults, except in point of size and the development of the reproductive sys tem. They are able to swim and feed im mediately, and resemble nothing save two large eyes attached to an infinitesimal streak of animated protoplasm that can dart 25 times its own length in the mi nutest fraction of a second. These har dier youngsters, for whom Nature makes no postnatal provision, thrive on pre pared baby-fish foods, desiccated egg yolk, cracker dust, and oatmeal broth. Males are generally smaller and more highly colored. Interbreeding has the same deteriorating effect as upon higher ani mals, and exchanges of breeding stock are made from time to time and new blood introduced through importations. Runts and giants occur in every batch, the for mer commonly disappearing down the gul lets of the latter, though as careful selec tion is practiced by fanciers as in the cul tivation of goldfishes and valuable plants. As yet, no purely albinistic stocks have appeared. The psychology of the fish has been barely touched upon, and almost any care ful observer may have the privilege of con tributing new knowledge, for every fish is a law unto itself. Pygmies sometimes ex hibit a discriminating sense of taste and an astonishing adaptability to change of environment, food, and temperature, and, when young, to the quality of the water they live in. Some are excitable; others phlegmatic; many active and playful. Some refuse to fight; others are incor rigible bullies. They learn most quickly where food is concerned and what time of day it may be expected. Some grow so tame they will swim into the hand; others never make human friends. Exemplifying the dim dawn of verte brate sensibilities, they display individual preferences and fierce jealousies; solici tude for their offspring or, in some cases, greater solicitude for the preservation of their own lives; some are curious and ob serving, showing an interest in form and color, being able to distinguish between shadows of friends and enemies and be tween the two ends of the spectrum-that is, between red, orange, or yellow as op posed to green, blue, or violet. The young fish able to swim concerns itself very early with a recognition of its own species, and schooling has been ob served among the fry of viviparous fishes less than a day old. DEVICES FOR CONVEYING AND CARING FOR TOY FISIIES Exportations of toy fishes from Ger many into the United States began about 25 years ago, numerous species having been first successfully bred in that country from parent stock captured in its tropical haunts. Though many thousands now are prop agated elsewhere, a large percentage of those owned in the United States being "home grown," considerable numbers, of a value variously estimated at from $50,000 to $Ioo,ooo per annum, still are shipped from Germany and South America. The typical German traveling can is of tin, with a capacity of about four gallons, heavily insulated with felt wadding and paper and with an opening in the cover to admit air. Thousands of specimens have traveled safely across the ocean and into the interior of the United States in these cans, most of the shipping being done be tween May and October. For conveying by hand or shipping specimens shorter dis tances, one-gallon thermos jugs are used.