Fish eggs can be transported via animals or birds.
The eggs 'stick' to the fur or scaled feet of the critters and end up falling
off in a new pond or water source. The eggs can also travel attached to
vegetation which in turn is transported in animal coats or in their paws or
feet.
Ornamental ponders are always accidently sending off fish eggs in plants
exchanges. Clams, mussels, insect larvae, tube worms, snails, leeches and
amphibian eggs have also traveled via this method.
This is probably what happened with your pond.
A wildlife fish biologist could probably tell you if bullheads would out
compete your bluegill and bass for food resources in your pond. I did find that
small fish make up a small part of the bullhead diet. They make good use of
varied food sources
which makes them successful in turbid ponds. And two other significant facts
One, they have few predators.:
Black bullheads have large, sharp spines at the front of their dorsal (top)
and pectoral (side) fins. When bothered, they lock them in a straight-out
position making them very hard to swallow. These spines and the fishes'
preference for eating mostly at night make black bullheads an uncommon prey for
other fish.
and as for algae and lack of clarity in your water right now,
It is a hardy fish that tolerates turbid (muddy) water, warm temperatures,
and low oxygen concentrations. The black bullhead can tolerate conditions many
other types of fish cannot.
Your pond's natural predilection is to fill in. It is mother nature's way of
providing for fertile fields. Your pond has been following this path for 20
years now and its becoming more of a habitat that bullheads enjoy. It may be
time to do some more excavating.

A really good book dealhe book on maintenance and renewal of older ponds. Some
starting as 'old' as ten years into the ponds life. Your pond at 20 years may
be a candidate for this.




Our pond is right at the edge of a 50 acre wetland. There is no stream
inlet or outlet. When we had the pond dug the excavator said it was
spring fed and you see two areas at the bottom that remained clear for
years. The pond filled in a couple days and the level varies very
little, even in the dry summer months. We bought the bluegills and bass
from a fish hatchery and put in no bullheads. And didn't see any for 20
years or more.
kathy :-)
A HREF="http://www.onceuponapond.com/"Once upon a pond/A