Why are my tropical fish swimming at the top of the tank

why are all my tropical fish always at the top instead of swimming all over, including the catfish
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Maui's western shores feature several of the best beaches for snorkeling and swimming. D. T. Fleming Beach Park features inner cove areas, plus a long stretch of white sandy beach. Past the sandbar is better for body boarding and surfing. Kapalua Beach is one of Maui's top beaches, offering calm waters within its sheltered lava-rock cove. Kahekili Beach Park is Maui's old airport strip and a favorite family beach destination. The shallower waters along the coast are perfect for swimming, and the reef on the outer shore offers a great place to snorkel, with its many brightly colored fish. Kaanapali Beach is a four-mile stretch of golden sand and aqua-blue waters. For snorkeling, swim out to the Black Rock area just offshore. Waters here are crystal clear and snorkelers will find numerous sea turtles, tropical fish and even the occasional octopus. Honolua Bay is a prime swimming location, and snorkeling is best on a clear, calm day. Coral formations along this beach feature hundreds of brilliantly colored tropical fish and a few sea turtles.
Swimming with schools of beautiful, colorful, tropical fish and green sea turtles is the top goal of any Maui snorkeling adventure
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With more than 30 miles of beaches, you'll never run out of fun activities to keep you busy when vacationing in Maui. Two of Maui's top water sports activities include snorkeling and casual swimming, and visitors will find that both are available along several of Maui's best beach areas. Wildlife you may encounter in Maui's clear blue waters include seals, dolphins, reef or whale sharks, sea turtles, manta rays and tropical fish. Stocking Your Aquarium Evenly - The Spruce
Photo provided by FlickrWhat community tank fish swim on the top of tank
Photo provided by FlickrThe vast majority of community fish are more mid-water swimmers
Photo provided by Flickr