The Aquarium exhibits the creatures that live in Lake Biwa, with a focus on fish.
Here you can see the creatures that inhabit reed beds, offshore areas of the lake, the depths of the lake, and the rivers that feed the lake. People have eaten fish from Lake Biwa since ancient times, and the aquarium introduces the techniques used for catching fish and for preparing fish eaten in this area.
Lake Biwa is one of the world's few an ancient lakes, and the Aquarium also introduces some of the other major ancient lakes of the world. In the Micro Aquarium you can see micro-organisms that support the Lake Biwa ecosystem.
In this tank you can see the reed bed environment and the crucian carp and carp family that inhabit the reed beds. Vast reed beds can be found on the shores of Lake Biwa and in the satellite lakes. In spring, ray-finned fish gather in the reed beds to lay eggs. These fish are used to prepare 'funazushi', a specialty sushi dish of Shiga Prefecture. Fishermen use 'tatsube' traps to catch schools of ray-finned fish. Numerous other fish and birds also come to the reed beds to reproduce. The reed beds from spring to summer bustle with a variety of life.
Lake Biwa away from the shore is wide and deep. In this tunnel tank you can see fish such as Biwa salmon and Japanese crucian carp, which can be found freely swimming in the waters offshore. The depth of the lake offshore is nearly 100 m. Below a depth of 20 m there is a cold layer of water, where the temperature is 18°C (64°F) or lower throughout the year. Creatures that like cold water inhabit this area. The tunnel tank keeps a cold temperature in order to show the energetic swimming of such fish.
A variety of fishing techniques are used offshore. This section introduces fishing using a 'koitoami', a type of gill net. 'Koitoami' fishing is a technique to stretch a net just like a curtain offshore where fish can be found. Depending on the size and type of fish, the size of the mesh and the net vary. Several installation methods are used. 'Koitoami' can be installed at the bottom of the lake or hung in mid water. Hemp thread was traditionally used to make the nets, but now synthetic filaments, such as nylon, are used.
In this tank, you can see a giant Lake Biwa catfish, the symbol of the Lake Biwa Museum. Lake Biwa catfish can grow over 1 m in length and weigh over 30 kg. This is the largest native species in Lake Biwa. This species is a nocturnal predator, spending the day at over 20 m depth and coming up into shallower water at night to prey on smaller fish. Lake Biwa catfish lay eggs along the rocky lakeshore in June, the rainy season in Japan, when the water level is high. The eggs are 2 mm in diameter. The young fry, 2 to 3 days after they are born, are tiny, less than 1 cm in length.
In this tank you can see the mysterious creatures that inhabit the deepest parts of Lake Biwa. At depths greater than 30 m, the water temperature is stable at around 10°C, 50°F, throughout the year. In contrast, surface temperatures change dramatically depending on the season. The isaza goby, a member of the goby family, moves between the surface water and the deep water every day in order to know the change in seasons and when the time is right for egg laying. Some fish stay deep in the lake to pass the winter. During the winter these fish avoid the shallows which become very cold. Some creatures which originated in cold regions inhabit the depths of the lake.
Sweetfish that live offshore are called koayu or small ayu, because they only grow up to 10 cm in length. You can see a school of koayu in this circular tank. Usually, sweetfish make their way down to the lake soon after they are born. From spring to early summer they mature while swimming upriver. However, koayu are different. They stay offshore in Lake Biwa until fall, when they head upriver to spawn. A lot of koayu inhabit the lake, and it is thought that the limited amount of plankton is why they do not grow larger. If koayu are released in a river they can grow larger because there are other foods available, such as moss attached to rocks.
In this section you can see species endemic to Lake Biwa, such as utsusemikajika, a sculpin, and Biwa-higai, the Biwa oily gudgeon. Many endemic species inhabit Lake Biwa because the lake has a history of four million years. Some of the fish and shellfish are edible and taste great. Fishing techniques to catch them effectively and recipes to enjoy these tasty species have been developed since long ago.
Fishing by hand is a popular activity. This section introduces changes in waterfront activities in the Lake Biwa area. Do you remember what kind of fish you caught when you were a child? The type of fish differed depending on the area, the season and the fishing method. The type of fish being caught also depends on your generation. Up until the end of the 1970's the lakeshore in spring was busy with people fishing for honmoroko minnows. However, recently we only see people lure fishing for largemouth bass.
In this tank you can see creatures that inhabit the lakeshore near the Lake Biwa Museum. The lakeshore and waterways between Kusatsu City and Moriyama City are full of species that originated from outside Japan, such as red swamp crayfish, red-eared sliders, large-mouth bass and bluegills. These species were artificially introduced to the lake for sport fishing and as unwanted pets. To native species such imported species are the same as invading aliens.
Many people think that all the alien species are from foreign countries, but actually species native to Japan are also alien species if they are transported and released in a place where such species never lived before. In order to differentiate these from species that originated in foreign countries, we call them alien species from Japan. In Lake Biwa, Japanese smelt is one example. Japanese smelt released to the lake by people is now an important resource for the local fishery. There are other fish from Lake Biwa that have become alien species in other parts of Japan.
This section introduces the current status of the Lake Biwa fishery. The fish catches in Lake Biwa from the late 19th century to the 1960s increased due to the development of fishing techniques and increased demand. However, since then the catches in the lake have decreased because of changes in the natural environment, an increasing number of invasive species and changes in demand. Many people, including fishermen, are now conducting activities to increase the catches in the lake.
The number of 'kawazakanaya', freshwater fish stores, has decreased recently. The opportunities to eat Lake Biwa fish have unfortunately diminished because of decreasing catches, and increasing availability of marine fish at markets. However, there are many tasty fish and shellfish in Lake Biwa, such as Biwa salmon, sweetfish and Seta freshwater clams, and fishermen catch them each season. 'Kawazakanaya' also sell prepared dishes, such as 'tsukudani' (simmered dishes with a soy sauce based soup), 'shioyaki' (salt-grilled fish) and 'sashimi' (raw slices of fresh fish).
In this tank you can see fish that inhabit the downstream of a river and the weir used to catch these fish. In rivers flowing into Lake Biwa a variety of fish go upstream depending on the season. From spring to summer, a weir is installed to catch fish, such as sweetfish, Japanese dace and three-lips, going upstream. In fall, sweetfish and Biwa salmon lay eggs downstream. In this section, depending on the season, you can enjoy different exhibits such as sweetfish and Japanese dace attempting to jump over the weir, and Biwa salmon laying eggs.
In this tank you can see creatures that inhabit the midstream of rivers. Sweetfish may be the first fish that comes to mind when considering fish that inhabit the midstream of rivers in Japan. Sweetfish that come upriver from the lake from spring to summer lay claim to territory around mossy rocks. The sweetfish dash to chase off other sweetfish approaching their territory. Ayu-no-tomozuri, a sweetfish fishing technique using a decoy, was developed by taking advantage of this behavior. In fall and winter, when sweetfish disappear from the rivers, other fish, such as pale chub and dark chub, are able to eat moss attached to the rocks. It might be difficult to see, but there is also a Japanese giant salamander in this tank.
Water that percolates from the mountain surface creates small streams. Several streams join to create the upstream of a river. You can see creatures that inhabit the upstream in this tank. Upstream, cold clear water rapidly dances and falls among the rocks and hollows. The landscape here is beautiful, but cold clear water is short of nutrients. The environment is not stable. For example, avalanches of rocks and earth can be caused by heavy rain. For this reason, few fish other than those such as char and 'amago' salmon that prefer oxygen-rich, cold water, live here. Because food is scarce for these fish they eat anything available, such as insects and other creatures falling from trees above the river surface.
In winter many waterfowl come to Lake Biwa. Some waterfowl stay in the lake throughout the year. In this tank you can see waterfowl that inhabit Lake Biwa. The little grebe, Shiga's prefectural bird, is the best-known bird in Lake Biwa. This small bird is about 25 cm long and inhabits the lake throughout the year. The bird dives underwater to catch small creatures, like fish and shrimp. Once a day, at around 1:15 PM, the birds are fed in this tank. You can see how skilfully little grebes submerge to catch fish.
This is the Fish Conservation and Breeding Center, another main feature of the Aquarium Gallery. Endangered fish from all over Japan are bred at the center. Approximately 40 kinds of fish, including those designated natural monuments in Japan, such as Ayumodoki, or kissing loach, and itasenpara bitterling, as well as fish on the Red List of the Ministry of the Environment or of Shiga Prefecture, have been bred here. In order to protect these fish and increase their numbers, fish are provided for exhibition and research through cooperation with zoos and other aquariums.
More than 1000 endemic species inhabit Lake Baikal, which is approximately 30 million years old. In this section you can see fish and other creatures that inhabit Lake Baikal. Sixty-one fish species inhabit Lake Baikal, 33 of which belong to the sculpin family. Moreover, 32 species of the sculpin family are endemic to Lake Baikal. Other fish include salmon, omul and grayling. These fish are important to the lake fishery.
In this tank you can see Baikal seals, the only exclusively freshwater seal species. As you can tell from its name, the Baikal seal is endemic to Lake Baikal. They are able to dive to depths of 400 m. They eat Baikal oilfish, one of the sculpin family. Baikal seals are distinguished by their large eyes, which help them see in the lake's deep waters. The temperature at Lake Baikal drops below minus 20°C (minus 4°F) in winter and the lake surface is covered by more than 1 m of ice. This is why Baikal seals have a thick layer of blubber under their fur and skin. They make holes in the ice with their sharp, hard forepaw claws.
This section introduces ancient lakes in the Great Rift Valley in Africa, Lake Tanganyika, Lake Malawi and Lake Victoria, and fish that inhabit these lakes, focusing on the cichlid family. In these lakes each species of the cichlid family has evolved resulting in many endemic species. These fish are colorful and have interesting behaviors, such as brooding young in their mouths. However, many species endemic to Lake Victoria became extinct when Nile perch, which can grow to nearly 2m in length, were released to promote the local fishery. Moreover, numerous trees were cut down in order to construct Nile perch processing factories, seriously impacting the surrounding ecosystem.
In this tank you can see living fossils, or ancient fish, such as sturgeons and gars. The first vertebrates that appeared on earth were fish. Between the end of the Silurian period, approximately 420 million years ago, and the beginning of the Devonian period, the ancestors of fish appeared. They have evolved into present day fish over a long period of time. Many species appeared in the course of evolution and many disappeared when they were out-competed by new species. Some, despite possessing ancient anatomy, have managed to survive. From around 3:40 PM, you can see sturgeon being fed in the tank.
In this section you can touch fish and crayfish. Let's get a sense of some creatures that you usually don't see up close. There is also another tank where you can touch creatures. The tank has an opening in the front where you can insert your hands.
When we think about life in Lake Biwa, we tend to focus on the large creatures and plants, such as the fish, turtles, shellfish, water birds, and water weed. These we can easily see with our own eyes, but these groups only form about 17% of the 1,800 species recorded from the lake. The rest, 83%, are tiny and usually go unnoticed by most people. The Micro Aquarium attempts to showcase the amazing variety of these hidden, tiny creatures living in Lake Biwa and Shiga Prefecture.
This two and a half meter long metal model is of Leptodora richardii, a water flea that eats other zooplankton, and which is found in Lake Biwa. They are only about one cm in length, but they are giants among the other plankton in the lake. Leptodora are almost transparent, so are very difficult for other plankton to see. They hang in the water column, and wait for unsuspecting prey items to swim past. When they detect prey, they grab it by using their appendages and curling their abdomen forwards. Although they are voracious predators, they are in turn eaten by fish. To the left are reliefs of other types of micro-creatures found in Lake Biwa. The sizes and shapes of the tiny creatures living in the lake is very diverse.
In this corner you can see some of the groups of tiny organisms that inhabit Lake Biwa. The types of organisms living in the lake vary from season to season. Some species appear only in summer, while others are found throughout the year. Consequently, the species displayed here are constantly changing. Fish and shellfish are usually not considered to be microorganisms, but when they are born, many are only the size of a water flea. Depending on the season, you can see freshly hatched examples of these here as well. For a more detailed look at some of the organisms, take a look into one of the microscopes at the Micro Bar. A staff member will assist you.
What does water feel like to you? What does water feel like to a tiny creature? Try moving the paddles in the two boxes in front of you. The one on the left represents water as humans and larger animals, such as fish, experience it. The one of the right is a highly viscous liquid, which represents water as tiny creatures experience it. At the micro-scale, water behaves and feels very differently to how we typically experience water. This is because the cohesion of water is very strong, so at a small scale it sticks together well. But at a larger scale, the cohesive forces are more easily overcome. So to a tiny creature, swimming through water feels like moving through syrup.
This panel introduces numerous types of tiny organisms that you have seen in the Micro Aquarium as well as their diverse activities. So far over 1,000 species of tiny organisms have been found in Lake Biwa. Their numbers are staggering. For example, there are approximately one million bacteria in 1 ml of water. Not only the shapes, but also the activities of tiny creatures are diverse. For example, the way they take in nourishment differs depending on the creature. Some use photosynthesis, some eat creatures smaller than themselves, some eat or decompose the dead bodies or waste of other creatures, some swallow creatures larger than themselves, and some adhere and decompose live algae.