68 GOLDFISH VARIETIES AND 
installed at moderate cost. These are extremely vauable in guarding 
against the dangers of sudden cold spells at night, particularly where 
tropical fishes are kept or when young goldfishes have been hatched in 
the late winter or early spring months. Oil stoves are not to be recom- 
mended and should only be used in emergencies. The carbonic product 
of combustion while small in quantity is, nevertheless, injurious. Water 
absorbs most gases very freely. 
The cement floors of fish houses should be provided with gutters next 
to the tanks, these all draining to a single point so that the floors can 
easily be flushed down. 
A description of methods of building concrete ponds and tanks will 
be found on page 220. 
Commercial Breeding of Tropical Fishes. The detailed descriptions 
of breeding habits described on pages 92 to 100 will give a practical 
working basis for anyone wishing to enter this field commercially. There 
are, however, a few generalizations which ought to be of value here. In 
Nature the fishes manage to reproduce themselves without the help of 
man. The three principal reasons are because they have water of the 
proper temperature, food of the right character and plenty of opportunity 
for the young to hide. All of the conditions can be produced artificially. 
The European breeders use tubs, introduce a thick growth of plants, place 
in One or more pairs of breeders as occasion demands, feed plenty of 
daphnia, mosquito larve, etc., and disturb the fishes as little as possible. 
In the absence of greenhouses the tubs are sunk in the ground, covered 
with wire netting in warm weather and with glass on cool nights or days. 
Quite large tanks are sometimes used, placing different species with the 
same breeding habits together, not attempting to sort out the various young 
until fall. In the livebearing groups there is no likelihood of hybridization 
if males and females of the same species are both present. Some fishes do 
not like plants and will tear them out (cichlide group, for instance), but 
as a rule the young very early appreciate their value and quickly hide 
among them. They also hunt sloping, shallow edges where the larger 
fishes cannot follow, particularly if Salvinia or other small floating plants 
are along the edge. 
A continuous, warm temperature is imperative for some species and 
for these it is not worth while attempting to breed outdoors in a temperate 
climate. 
In selecting a stock to breed from for commercial purposes it is 
inadvisable to choose the species which have already become common, even 
though they are easy to breed. It is much better to pay more for some- 
thing out of the ordinary if there seems to be a reasonable chance of 
breeding it. The “fashions” change so rapidly in tropical fishes that we 
could not attempt here to advise what to breed, as our book would be likely 
to look old by the time it is off press. 
