New Fishes from CTY

CTY Aquarium actually gives out discount coupons for one's birthday - RM15 discount for a minimum purchase of RM30 which works out to be 50%. So on Sat, I went with mun & dad to pick up another 30 fishes (4 species), a packet of fish food and 3m of cleaning tubes. Suddenly, our home aquarium looks overcrowded, ha ha. They were all so excited with their new home. However, at the end of the first 24 hours, 3 kaput followed by another 4 more ... is it the overcrowding or some unexplained phenomena.

By the way, is it fish or fishes?
Wikipedia Terminology : Though often used interchangeably, these words have different meanings. Fish is used either as singular noun or to describe a group of specimens from a single species. Fishes describes a group of different species.