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LAS VEGAS — <\/span>When Becky O\u2019Brien dangles herring over a tank of over a dozen swimming sharks, it only takes seconds for a zebra shark<\/a> to snatch the fish from her tongs.<\/p>\n The lead aquarist said she always knew she wanted to work with marine life; she just didn\u2019t think she\u2019d be a shark dietitian at a 1.3 million gallon tank and Las Vegas casino. O’Brien’s team feeds 15 species of sharks three times a week at the Shark Reef Aquarium at the Mandalay Bay Resort, where they tend to over 3,400 animals.<\/p>\n \u201cThey eat, I would say, better than the tourists on the Strip,\u201d O\u2019Brien said, referring to the gourmet restaurants in Las Vegas’ biggest tourism hub. <\/p>\n The aquarium is a major tourist attraction that has drawn over 21 million visitors to the resort and casino since it first opened in 2000, according to Mandalay Bay.<\/p>\n Sharks’ diets consist of proteins and lipids in order to maintain their fatty livers, which allow them to move up and down in the water, said Samantha Leigh, a professor at California State University, Dominguez Hills, who focuses on marine animal nutritional physiology.<\/p>\n In the wild, sharks eat a diverse mix of prey across the food web, ranging from microscopic zooplankton to seals and even other sharks, Leigh said. In captivity, many sharks are fed restaurant-quality seafood, she said. <\/p>\n The sharks at Mandalay Bay are fed a mix of mackerel, herring, blue runner and sardines in an effort to give them a varied diet like they\u2019d have in the wild, O\u2019Brien said. Some of the fish are wild-caught, while others come from sustainable fisheries, she said. <\/p>\n In one week the aquarium goes through over 300 pounds (136 kilograms) of fish, O\u2019Brien said.<\/p>\n The fish are stuffed with vitamins, and they need to be hidden in the food to ensure the animals won\u2019t spit them out \u2014 the staff\u2019s version of giving a dog its medicine covered in peanut butter, O\u2019Brien said.<\/p>\n Also like dogs, the sharks are trained to be rewarded with food for specific behaviors. The zebra sharks touch a target in order to receive food, and animals learn to go to specific areas of the tank for their meals.<\/p>\n Lunchtime provides a chance for the staff to examine the animals. They can tell a lot about the sharks\u2019 conditions based on how they\u2019re eating. If they turn down food, they may have an illness, or they may be interested in mating, O\u2019Brien said.<\/p>\n Sharks are ravenous before breeding season, but many of the male sharks will eat little during the season, which runs from March to June.<\/p>\n \u201cOnce you get to work with these guys on a daily basis, you do learn little nuances of how each one feeds a little bit differently,\u201d O\u2019Brien said. \u201cEach species is a little bit different.\u201d<\/p>\n