Paradise Threadfin

Polynemus paradiseus

FreshwaterBrackishFish

Care at a glance

Temperature: 75–82°F (24–28°C)
pH: 6.5–8.0
Adult size: 9.8 in (25 cm)
Minimum tank: 75 gal (285 L)
Temperament: Mostly peaceful
Social behavior: Social
Swim level: Bottom
Difficulty: Difficult
Breeding: No record
Rarity: Very rare
Origin: South Asia, South East Asia
Family: Polynemidae

Overview

The paradise threadfin is a peaceful, social fish best kept in a group, since lone fish are nervous and it does no harm to its own kind. It is gentle toward tankmates too, but its long, trailing pectoral filaments are easily nipped, so avoid fin-nippers and pushy fish. It is an active swimmer that feeds along the bottom, feeling for food with those threads, so give it open sandy floor and swimming room. Feed meaty foods such as brine and mysis shrimp, chopped prawn, mussel, and earthworm pieces, offering live foods at first if needed. A group needs a large, open tank of around 285 liters or more, and the fish stays healthiest with some salt in the water.

In the wild

The paradise threadfin lives in the tidal rivers and estuaries of South and Southeast Asia, moving through murky, brackish water and returning to fresh water to spawn. It is a euryhaline fish, and although it can survive in fresh water, most keepers find it delicate unless a little salt is added, at a low to moderate brackish strength. Give it warm water from 24 to 28 C, a hard and neutral to alkaline pH between 6.5 and 8, and an open tank with a soft sand floor and few obstacles so it has room to swim. Keep the water clean and well filtered.

Good to know

The paradise threadfin belongs to the family Polynemidae, the threadfins. Its common name comes from several long, free filaments that hang from the base of each pectoral fin and trail well past the body. These threads are sensory organs the fish uses to feel for food in cloudy water where sight is of little use. Adults reach around 25 cm. Breeding is undocumented in aquariums, and the species is thought to move between brackish and fresh water to spawn in the wild.

Did you know

The paradise threadfin trails several long thread-like filaments from its pectoral fins, some longer than its whole body. Far from being decoration, these threads are feelers packed with sensory cells that let the fish taste and touch its way to food along the bottom of murky, tea-colored estuaries where it can barely see.