Actinopterygii (ray-finned fishes) > Perciformes
(Perch-likes) > Polynemidae
Etymology: Eleutheronema: Greek, eleutheros = free + Greek, nema = filament (Ref. 45335).
Environment / Climate / Range
Marine; freshwater; brackish; pelagic-neritic; amphidromous (Ref. 51243); depth range 0 - 23 m (Ref. 6390). Tropical, preferred 28°C (Ref. 107945); 32°N - 26°S, 47°E - 154°E (Ref. 57343)
Indo-West Pacific: Persian Gulf to Papua New Guinea and northern Australia. Replaced by Eleutheronema rhadinum (Jordan & Evermann, 1902), in East Asia (Japan, China, Viet Nam).
Length at first maturity / Size / Weight / Age
Maturity: Lm ?, range 29 - ? cm
Max length : 200 cm TL male/unsexed; (Ref. 3479); common length : 50.0 cm TL male/unsexed; (Ref. 3479); max. published weight: 145.0 kg (Ref. 4965)
soft rays: 14 - 16. Pectoral filaments 4; fin membranes vivid yellow in life, except in large specimens, > ca 35 cm SL. Vomer with deciduous tooth plates on both sides, except in juveniles. Posterior part of maxilla deep, 3-4% of SL. Short tooth plate extension onto lateral surface of lower jaw. 7-9% SL (Ref. 41639).
Adults occur mainly over shallow muddy bottoms in coastal waters. Also enter rivers (Ref. 3479, 6390, 11230). Juveniles found in estuaries. During winter, adults ascend the rivers. They usually form loose schools, although larger fish are more often observed in pairs or singly (Ref. 6390). Feed on prawns and fish (largely members of Mugilidae, Engraulidae, and Sciaenidae) with occasional polychaetes. Frequency of crustaceans to fish in the diet varies seasonally. Larvae (7-30 mm TL) feed mainly on copepods and mysids but also take shrimps and prawn larvae (Ref. 57343). Juveniles (31-60 TL) feed on prawns shrimps and mysids (Ref. 57343). Protandrous hermaphrodites. Marketed fresh, frozen, and dried or salted.
In Australia, fish are males at 24-47 cm FL, hermaphrodites at 25-46 cm FL and females at 28-72 cm FL. On the northeast Queensland coast, most blue threadfin are females by 45-50 cm FL. Hermaphroditic blue threadfin develop fom 1-2-year-old fish, and females first appear as 2-3-year-old individuals (Ref. 28736). Male fish probably commence sex reversal immediately after spawning (ie about April-May) and this condition may persist until after the next spawning period (Ref. 28736). The progression from hermaphrodites to females is complete by the following season.
There is little information on the larvae, although nursery areas are known to be lower estuaries, tidal swamps and lagoons, and shallows along the foreshores (Williams 1997).
Motomura, H., Y. Iwatsuki, S. Kimura and T. Yoshino, 2002. Revision of the Indo-West Pacific polynemid fish genus Eleutheronema (Teleostei: Perciformes). Ichthyol. Res. 49(1):47-61. (Ref. 41639)
IUCN Red List Status (Ref. 109396)
CITES (Ref. 94142)
Threat to humans
Fisheries: highly commercial; aquaculture: commercial
Estimates of some properties based on models
Phylogenetic diversity index (Ref. 82805
= 0.6250 [Uniqueness, from 0.5 = low to 2.0 = high].
Bayesian length-weight: a=0.00389 (0.00180 - 0.00842), b=3.12 (2.94 - 3.30), based on all LWR estimates for this body shape (Ref. 93245
Trophic Level (Ref. 69278
): 4.1 ±0.5 se; Based on diet studies.
Resilience (Ref. 69278
): Medium, minimum population doubling time 1.4 - 4.4 years (Fec=680,000; assuming tm>=2).
Vulnerability (Ref. 59153
): High to very high vulnerability (69 of 100) .