First of all, we have to start with the aquatic plants. Aquatic plants are not just thrown into the water casually. They are the "forest" of fish and their playground. Imagine how boring it would be if you were in a park without rides! Therefore, the placement of aquatic plants must be given priority. We can divide aquatic plants into different areas, just like the city's planning. In one corner of the aquarium, put a tall aquatic grass, like a dense forest. The fish can travel here just like we are exploring in the forest. They can hide behind the water plants, play hide-and-seek with their companions, or secretly observe the outside world. Moreover, the tall aquatic plants can also give the fish a sense of security, just like we hide behind the curtains and peek outside, we are both nervous and excited.

On the other side of the aquatic plants, we can put some short, fluffy aquatic plants, like a grassland. Fish can roll on it, somersault, or bask in the sun here. Don’t think that fish don’t bask in the sun, they also need warm sunshine to replenish energy. Moreover, short aquatic plants can make it easier for fish to find food, just like we look for mushrooms on the grass. They can shuttle between the aquatic plants, gently tweak the aquatic plants with their mouths, looking for the delicious little bugs hidden inside. In this way, the fish's activity volume has increased greatly. They no longer have to swim around bored all day, but have their own "playground".

Of course, it is not enough to have aquatic plants alone. We also need some pipelines to increase the fun of the fish. Pipelines are not just "highways" for fish, they are also "secret passages" for fish. Imagine how excited you would be if you suddenly find a secret passage in a maze! The same goes for the fish. We can design pipes into various shapes, some straight, some curved, and some like spirals. The fish can enter through one pipe opening, then turn around the pipe, and finally come out from another pipe opening, like playing a maze game. Moreover, the pipes can connect different areas, allowing the fish to shuttle more freely. For example, fish can go through pipes from the "forest" area to the "grassland" area, or go through pipes from the "grassland" area to the "coral reef" area. In this way, the range of activities of the fish is greatly increased, and they can explore freely between different areas and no longer have to be confined to a small space.

Moreover, the pipes can also bring some stimulation to the fish. We can design the pipes to be sloped so that the fish can slide in the pipes. Imagine the fishes gliding quickly in the pipes, just like we are on the slide, and that sense of speed and thrill will make them excited. Alternatively, we can also put some small stones or shells in the pipes so that the fish can touch these things and make some noise when swimming in the pipes. In this way, the fish will find it very fun, just like we are playing with a toy with sound.

In addition to aquatic plants and pipes, we can also put some decorations in the aquarium to increase the fish's activity space. For example, we can put some fake coral reefs so that the fish can drill around in it. Coral reefs can be designed in various shapes, some like castles, some like mazes, and some like caves. Fish can travel through the gaps in the reefs or hide in the corners of the reefs to rest. Moreover, coral reefs can provide fish with a shelter where they can hide from danger. For example, when fish see danger outside, they can quickly hide in coral reefs, just like we hide in air raid shelters when we encounter danger.

We can also put some small stones in the aquarium so that the fish can rest or bask in the sun. Small stones can be designed in various shapes, some like hills, some like islands, and some like small bridges. Fish can rest on small stones, or shuttle between small stones, looking for food. Moreover, the small stone can also provide fish with a place to grind their teeth. Fish sometimes bite the small stones with their mouths, just like we are eating gum, which can keep their teeth healthy.

Of course, we can also put some small toys in the aquarium to increase the fun of the fish. For example, we can put some small balls so that the fish can push them around. The fish can gently bite the ball with their mouths and push it hard to let the ball roll in the water. Imagine that the fish are pushing balls in the water, just like we are playing football, how fun it is! Or we can put some small windmills so that the fish can blow it. Fish can blow the small windmill with their mouths to make the small windmill rotate in the water. In this way, the fish will find it very fun, just like we are playing with a small toy with wind.

Moreover, we can also put some small mirrors in the aquarium so that the fish can see their reflections. The fish sometimes look at their reflections in the mirror, just like we are looking in the mirror. They will feel good and then swim around in the water to show their beauty. Moreover, the small mirror can also provide fish with a way to entertain. Sometimes the fish will play hide-and-seek with their reflections or fight with their reflections. Although this looks silly, the fish are enjoying it.

When designing a fish activity space, we also need to consider the types and habits of the fish. Different fish have different preferences. Some fish like to shuttle through the water plants, some fish like to slide in the pipes, and some fish like to rest on the stones. Therefore, we need to design a space suitable for fish according to their species and habits. For example, for those fish that like to shuttle through the aquatic plants, we can put more aquatic plants so that they have more places to explore. For those fish who like to slide in the pipe, we can design more sloped pipes to make them more exciting. For those fish who like to rest on stones, we can put more small stones so that they have more places to rest.

Moreover, we need to consider the size and number of fish. If the fish is too big and the pipe is too small, the fish will not be able to enter. If there are too many fish and the space for movement is too small, the fish will crowd each other and affect their lives. Therefore, we need to design the appropriate activity space according to the size and number of fish. For example, for those larger fish, we can design some larger pipes and aquatic plants areas to give them enough space to move. For those fish with more, we can design some larger activity spaces so that they can freely shuttle without crowding each other.

When designing the fish's activity space, we also need to consider the water quality and temperature of the aquarium. If the water quality is not good, the fish will get sick and will not be able to enjoy their space for movement. If the temperature is not right, the fish will feel uncomfortable and will also affect their activity. Therefore, we need to clean the aquarium regularly to keep the water clean. We also need to adjust the temperature of the aquarium according to the species and habits of the fish, so that the fish can live in a comfortable environment.

In short, designing a fun activity space for fish can not only increase their activity volume, but also make their lives more colorful. The fish are no longer the little guy who swam around bored all day, but become a vibrant and exploratory little explorer. They can shuttle through water plants, slide in pipes, rest on stones, and play in toys. They can play hide-and-seek with their companions and explore the unknown world together. They can find their own happiness and freedom in this small aquarium.