Adaptive value

The candiru lives primarily in an area where two
rivers mix, producing a great variation in pH, flora, and thus fauna.
Since the candiru cannot depend on a specific species to be constantly
available, specialization through type of prey would be unfortunate,
so the fish has specialized through its manner of predation. The
spines on its body allow it to lodge itself in its prey's body and
opens the skin to begin blood flow. The tracing of ammonia currents
signifies an animal with opened membranes nearby, which is the best
chance the candiru has to get to a source of blood quickly.