Keeping fresh water aquarium fish had been a childhood hobby. The 4 fishes shown are Harlequin rasbora, Pearl gourami, Malaysian Mahseer or Kelah or Wangbuliao which is an expensive edible fish too, and Golden Arowana kept for good fortune by business community and homes.
I visited 4 post offices in 3 states. PULAU PINANG - George Town General Post Office in Penang Island; TAMAN CHAI LENG in Penang Mainland as "CHAI LENG" sounds like "kim leng" - the Chinese Hokkein pronounciation of golden arowana; SUNGAI PETANI in Kedah as "Sungai" is "River" in Malay; and PARIT BUNTAR in Perak as "Parit" is "Drain or Canal" in Malay. Freshwater fish lives in rivers and drains/canals.
I also included the previous 2016 stamp issue of Seven Wonders of Malaysia's Flora & Fauna of Malaysian Mahseer (Kelah )to create hybrid FDC. Enjoy viewing.