Pairoj Sirimontaporn *
1. Introduction
Seabass, Lates calcarifer, is an economically important food fish in tropical countries. It is a species with catadromous habits within its areas of distribution. Studies on the biology and fisheries of the species are still in progress but the possibility of its culture has been established and undergoing development.
2. Taxonomy
The recently accepted taxonomic classification of seabass is as follows:
3. Morphometric Characters of Seabass and Related Species
Lates calcarifer (FAO, 1974)
Body oblong—elongate, compressed, with a deep caudal peduncle. Head pointed, with concave dorsal profile becoming convex in front of dorsal fin. Mouth large, slightly oblique; lower jaw projecting, upper jaw reaching to behind eye. Teeth villiform, no canine. Lower edge of pre—operculum with strong spine; operculum with a small spine and with a serrated flap above origin of lateral line. Dorsal fin with 7–9 spines and 10–11 soft rays; a very deep notch dividing spine from soft part of fin; dorsal and anal have scaly sheaths, anal fin round with 3 spines and 7–8 soft rays; caudal fin round. Scales large, ctenoid.
Colour: adult with olive brown sides and a silvery belly; juvenile stage, body with 3–4 black transverse bars and disappear when the fish grow to adult.
* Senior Fishery Biologist, National Institute of Coastal Aquaculture (NICA), Songkhla, Thailand
Psamperca waigienses (Cavier)
Body oblong compressed. Mouth large, jaw equal; upper jaw reaching to below eye. Tongue with patch of small teeth; lower edge of operculum smooth.
Distinguishing characteristics of Lates and Psanmoperca.
| Item | Lates | Psanmoperca | |
| 1. | Soft dorsal rays | 11 | 13–14 |
| 2. | Jaws | lower jaw projecting | equal |
| 3. | Lower margin of preoperculum | with three spines | smooth |
| 4. | Maxillary | beyond posterior margin of eye | extending to level of eye |
3. Distribution
The species is widely distributed in the tropical and subtropical areas of the western Pacific and Indian ocean. Its range of distribution includes the areas from Australia, Southeast Asia, the Philippines and countries bordering the Arabian sea.
4. Biology and Life History
The euryhaline (can live in fresh, brackish and marine environments) and catadromous (grows to maturity in fresh or brackish waters and spawns in the sea) characteristics of the species result in a very interesting ecological distribution at various stages of its life history. The fish spend most of their life in a lagoon which connects to the sea. They spend two to three more years in estuarine areas until they mature, then migrate to the sea water around the mouth of a river or lagoon for spawning. Larvae and juveniles live in the sea grass bed in coastal areas for about six months, attaining a size of about 2 to 5 inches. The fish migrate to freshwater when they grow bigger. Spawners live in coastal rocky shores but some migrate to a freshwater body after the spawning is over.
5. Feeding Habits
The adult fish is regarded as carnivorous, but juveniles are omnivorous. Analysis of stomach content of wild seabass (1 to 10 cm) found 20 % phytoplankton and the rest are small fish and shrimp. The larger fish consists of 100 % animal prey, 70 % crustacean and 30 % small fish (Wongsomnuk 1969 and Bhatia 1971).
6. Fecundity and Spawning
Fecundity of seabass is related to the weight of the fish. Females of the weight from 5.5 to 11 kgs gave 2.1 to 7.1 million eggs as indicated below (Wongsomnuk and Maneewong 1974).
| TL. (cm.) | Weight (kg.) | No. of fish | No. of eggs Range | Average |
| 70–75 | 5.5 | 3 | 2.7–3.3 | 3.1 |
| 76–80 | 8.1 | 5 | 3.1–3.8 | 3.2 |
| 81–85 | 9.1 | 4 | 5.8–8.1 | 7.2 |
| 86–90 | 10.5 | 3 | 7.9–8.3 | 8.1 |
| 91–95 | 11.0 | 3 | 4.8–7.1 | 5.9 |
Spawning of seabass in Thailand is year—round, but the peak occurs during April—September in the mouth area of Songkhla Lake. A large number of fry can be collected during May—August along the coast and seabass bed areas close to the lake entrance.
7. Sexual Maturity
In Songkhla Lake, fully mature fish grow to 70–90 cm; fish over 100 cm seem to be over—ripe. Sex inversion has not been examined (Wongsomnuk 1969).
