The life in Lake Biwa 1

What kinds of animals can be found in and around Lake Biwa?The lake is a living museum of fish, mollusks and plankton.

Plankton

plankton is a small life form that drifts suspended in water. There are about 200 species of phytoplankton and 120 species of zooplankton in Lake Biwa.

Phytoplankton has an important job as the foundation of the food chain in Lake Biwa. Phytoplankton are eaten by zooplankton, which in turn become food for small fish and mollusks.

Some species of zooplankton have a defensive mechanism to avoid capture or ingestion by predators.
There are many types in their defensive mechanisms; increase in swimming speed, and change to body shape.
For example, a species of water flea Daphnia galeata (Japanese name Kabuto mijinko), which commonly appear in many lakes and ponds, elongates helmet to protect themselves from various enemies.

Benthic invertebrate

Lake Biwa’s benthic invertebrate account for one third (700) of all the specied living in the lake and two thirds (38) of all the endemic species. The majority (29) of these of endemic benthic species are mollusks.

Fish

65 species of fish are native to Shiga Prefecture and 45 of these are found in Lake Biwa. In particular, 16 of the fish species have survived in the lake from its ancient beginnings.

In the unique environment of Lake Biwa, 2 types of endemic species have developed.

Fish evolved in the unique environment 

Fish that live in offshore and rocky areas different from other environments evolved as they established their own unique life systems. Biwa minnow and Sugo gudgeon probably originally evolved from fish living in nearby rivers and became new species in Lake Biwa. This kind of speciation is called initial endemic speciation.

Fish survived in Lake Biwa

There was also speciation in the ancient Lake Biwa and some of those fish species survive to this day. Biwa catfish, Deepbodied crucian carp, and Biwa culter are well known examples of this kind of relic endemic species evolution.

Shiga Prefecture is trying to exterminate invasive alien species, such as largemouth bass and blue gill, because they prey on the native fish and shrimp and cause serious damage to the natural environment.

(Small fish and shrimp from largemouth bass’s stomach→)