Tales usually take between 300,000 and 350,000 food, total. Here's the feeding charts for Seafish and Adrift Princess. (I hate math and was too lazy to add it all up
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Each level shows the total for all 5 bites of food.
Mantaray will need a little food, too- something like 1500-2000 total, so not a lot. These guys are actually on some of the cheaper feeding schedules, so the total this time is probably on the lower end of average Tales food costs.
*Addition: just checked, and these food costs look to be the same as the last two Tales- same feeding schedules.