5 Rupees Harlequin rasbora

Indonesia's long-running conservation coin program has produced numerous biodiversity-themed issues, but the freshwater fish series occupies a specific policy niche — these coins were introduced partly in response to international criticism of Indonesia's deforestation record, offering a form of soft diplomatic signaling through monetary issue. The harlequin rasbora (Trigonostigma heteromorpha) is native to the blackwater streams of Sumatra and the Malay Peninsula, where tannin-stained, acidic water produces the low-visibility conditions the species evolved for.

Bank Indonesia has issued commemorative five-rupiah denominations sporadically since the 1970s, though by 2019 the face value was essentially ceremonial — a single US cent buys roughly 140 rupiah at contemporary rates.