\"Is there any fish I have to be careful of in particular?\" I ask Veerachart Pimpat, head diver at the aquarium after noticing a dozen arapaima, another dozen giant catfish, plus hundreds of other fish notorious for their fierce habits, in the big tank. \"No, they are all friendly. I feed them with my hand every day,\" he replies before making bubbles, then dives into the water. We descend down into the gigantic tank, which is about 120m long and 4m deep. I find myself in a lively pool where thousands of remarkably big fish roam. A number of the Mekong giant catfish (pla buk), the world\'s biggest freshwater fish, measuring around 2m in length, make their way towards me. In spite of their size, they seem active and speedy. They have big mouths, wide enough to swallow me in one gulp. Thank goodness they feed on algae. Now and then, the Siamese giant carp (pla kraho) show up. It is the biggest fish in the Chao Phraya river basin. I then notice another huge fish from the river, a giant freshwater whipray (pla kraben rahu), lying peacefully on the tank\'s floor. As the world\'s biggest freshwater ray with a body as wide as 2m, it can easily blanket me. I am quite nervous when encountering the clown knifefish (pla kray), arowana (pla tapad) and giant gourami (pla raed). They are known for their aggressive behaviour and bite those who invade their habitat. Fortunately, those I find in the aquarium tank are in a good mood. Encountering the biggest fish from the American continent is the most exciting experience. Arapaimas in this tank are normally more than 2m long. They move slowly around, showing their red tail. I learn they can jump out of the water into the air, to the height of their body length, to catch monkeys on overhanging branches. I guess they are probably curious, as they keep hanging around me. One comes close enough for me to notice its pupils and the wrinkle on its head. I hope the dive suit makes me look different to a monkey. In the tank, there are many fish we can easily find on ice in a market, but it\'s quite hard to encounter them alive and swimming. For example, we usually meet clown knifefish in fish cakes. As well as the giant freshwater whipray, the knifefish is always found in marketplaces along the Chao Phraya river basin. \"You see the fish [look] bigger than when watching from the glass tunnel, don\'t you? That is the effect of the concave lens of the glass,\" an aquarium staff member explains after the dive. \"The fish we have are enormous in size. It is a pity that most visitors see them 30% smaller when looking through the glass tunnel.\" Besides schools of big freshwater fish, the aquarium has various rare and interesting varieties from around the globe, for example, Bengal freshwater eels (pla sa ngae) from the Salween River basin _ they live in the river but lay eggs in the sea _ and sword minnow. The aquarium has a marine tank as well, but I found it a bit boring. There is a handful of blacktip sharks, leopard sharks, and other fish that are shy during the day. I was glad to have chosen a dive in the freshwater tank. The complex also has interesting sea creature exhibitions. One of the unique displays involves cownose rays, which are harmless and playful. Visitors can feed, touch and play with them. It seems the rays always show up for tourists. Overall, Chiang Mai Zoo Aquarium reveals a world of fish you may otherwise never have known. MORE INFO - Chiang Mai Zoo Aquarium is located in Chiang Mai Zoo, on Huay Kaew Road. It\'s open Mon-Fri 10am-4pm, and Sat-Sun and public holidays 9am-4.30pm. - Admission fee: Adults 290 baht and kids 190 baht, including the zoo entrance fee. - Scuba diving in the tank costs 4,290 baht, including all entrance fees and gear. Divrs must show their diver licence. Advance booking is required. www.chiangmaiaquarium.com From bangkokpost