The larger animals which inhabit the mighty river and the network of
streams and pools which surround it on both sides, have been described;
but numerous smaller creatures dwell within it, equally curious, and
many totally unlike those to be found in other parts of the world. It
has generally been supposed that, of all creatures, fish are the most
destitute of parental feelings, and that from the moment the eggs have
been deposited in the sand or mud, they are allowed to struggle into
existence as best they can, to do battle with their foes, and the
numerous dangers to which they are exposed. In the acara, however, we
have an example of parental care and watchfulness unrivalled by any
terrestrial animal.
The male of this curious fish has a conspicuous protuberance on the
forehead, wholly awanting in the female and the young. Somehow or
other, the eggs of the female are conveyed into the mouth of the male,
the bottom of which is lined by them, between the inner appendages of
the branchial arches, and especially into a pouch formed by the upper
pharyngeals, which they completely fill. They are there hatched; and
the little ones, freed from the egg, are developed until they are in a
condition to provide for their own existence. In their head there is a
special lobe of the brain, similar to those of the triglas, which sends
large nerves to that part of the gills protecting the young, thus
connecting the care of the offspring with the organ of intelligence. In
this curious cavity of the father's head the young fish are found in all
stages of development,--the more advanced, a quarter of an inch long,
and able to swim about, full of life and activity. These appear to
exist outside the gills, within the cavity formed by the gill-coverts
and the wide branchiostigal membrane. The eggs remain in the back part
of the gills.
The parent's care does not appear to cease even when the young are fully
developed, but he allows them to swim in and out, and try their powers,
if not to search for food; and when danger appears, opens his mouth,
when they all swim back again in a shoal, for safety. The natives
assert that some species, at all events, are not actually developed in
the parent's head, but are laid and hatched in the sand, the male and
female watching carefully over them; and that the father only takes
charge of them when they are hatched, and receives them within his mouth
to protect them from danger. From the observations of Professor
Agassiz, however, there is no doubt that in some species, at least, the
whole process of development is begun and completed in the gill cavity.
The species which lay their eggs in the sand belong to the genera
Hydrogonus and Choetobranchus. They build a kind of flat nest in the
sand or mud, in which they deposit their eggs, hovering over them until
the young are hatched.
Curious also is the little bill-fish--the lymnobellus--with its long
beak.
Another fish (the anojas), common in the Amazon, takes shelter--for it
cannot be said to build a nest--in a hollow log. It belongs to the
genus Auchenipterus. Numbers of this fish are found crowded in dead
logs at the bottom of the river. One examined by the Professor, was
filled with fish of all sizes, from those several inches long to the
tiniest young. The fish were so dexterously packed into the log from
one end to the other, that it was impossible to get them out without
splitting it open, when they were all found alive and in a perfectly
good condition. They could not have been jammed artificially into the
hollow wood in that way without injuring them.