(Bloch)
(AND OTHER SNAPPERS FROM THE MANGROVES)
1. Distinctive characteristics of early developmental stages
(a) Eggs and larvae
No information from the mangroves.
(b) Early juveniles of Lutjanus johni (description based on 36 mm T.L. specimens)
Lutjanus johni 1
The body is moderately deep. The dorsal fin has 10 spines and 13 rays. The anal fin has 3 spines and 8 rays. The anal fin is somewhat semi-oval in shape. A distinct large black blotch is present above the lateral line and below the 2nd and 8th ray of the dorsal. A brilliant pearly ring is present around the blotch (the black blotch and pearly layer gradually disappear as the fish approaches around 15-20 cm in length. Specimens measuring above 20 cm in length have a dark spot on each scale and the scales with pigment provide a series of non-overlapping and undisrupted streaks horizontally from the posterior border of the head towards the caudal base).
2. Distinguishing characteristics of early developmental stages in similar species occurring in the mangroves
(a) Early juveniles of Lutjanus fulviflammus
Lutjanus fulviflammus 1
A black blotch is present below the first four rays of the soft dorsal fin and on the lateral line. About half the area of the blotch lies above and the rest below the lateral line. A pearly border is absent around the black blotch. About five longitudinal golden lines/stripes are present on the body, all below the lateral line. The golden stripes do not extend to the head region. The head profile is yet to become convex. In juveniles and adults, the longitudinal scale rows are parallel to the dorsal profile below the lateral line and rise steeply to the dorsal profile above the lateral line. The soft dorsal fin has 12-13 rays. The pectoral fin length is shorter in proportion when compared to that of adults (recorded from many mangroves within the Indo-West Pacific).
(b) Early juveniles of Lutjanus russelli
A black blotch is present on the lateral line with two thirds of the area of the blotch above the lateral line. The blotch is located below the first five rays of the soft part of the dorsal. A pearly layer is absent around the black blotch. Around 6-8 golden coloured lines are present on the body, of which the lower lines run horizontally and the upper ones arise from the post-orbital region towards the dorsal profile in an oblique manner. The soft dorsal fin has 14-15 rays (recorded from many mangroves within the Indo-West Pacific).
(c) Early juveniles and juveniles of Lutjanus argentimaculatus
Blotches are absent in the body. Early juveniles and juveniles have a brilliant and attractive blueish-grey colouring with silvery white crossbars (usually reddish or reddish-brown without any white crossbars in adults). Longitudinal rows of scales below the lateral line are horizontal, while those above the lateral line are parallel to the dorsal profile up to half the distance and rise obliquely towards the soft dorsal (widely occurring in the mangroves of the Indo-Pacific and are even known as ‘Mangrove jack’).
(d) Juveniles of Lutjanus fulvus
There is no blotch on the body. The caudal fin is black with a narrow white margin (reported only from the Philippine mangroves, although distributed widely throughout the East Indian Ocean and the Western Pacific)
(e) Juveniles of Lutjanus lemniscatus
Longitudinal rows of scales above the lateral line appear to rise obliquely upwards towards the dorsal profile and those below the lateral line run horizontally (recorded from the Southeast Indian mangroves) (Jeyaseelan, 1981).
(f) Juveniles of lutjanus rivulatus
In the head region, numerous alternating yellow and blue wavy lines are present. An unusual white spot bordered by black pigmentation is present on the lateral line below the origin of the soft dorsal. (Though this species is distributed widely throughout the Eastern Indian ocean and Western central Pacific, it is reported from the mangroves of the Philippines alone and not from any other mangroves).
(g) Juveniles of Lutjanus sebae
The body is pinkish. Three broad transverse bands are present and are dark red in colour. The first band runs between the snout and the first spine of the dorsal fin. The second band originates at the tip of spinous dorsal fin and runs down and occupies the entire area between the pelvic and anal fins in the ventral profile. The third one runs from the junction of the spinous and soft dorsal fin to the tip of the posterior part of the caudal lobe (recorded from the mangroves of the Southeast Indian coast) (Jeyaseelan, 1981).
(h) Juveniles of Lutjanus vittus
There is no blotch on the body. A dark band is present, extending from the posterior part of the eye to the upper part of the caudal peduncle (juveniles are reported from the mangroves of Singapore alone and not from any other mangrove).
3. Distinguishing characteristics of similar species occurring in the adjacent coastal and coral environment
(a) Juveniles of Lutjanus coeruleolineatus
The spinous portion of the dorsal fin has only 10 spines. About two thirds of the area of black blotches lies above the lateral line and the rest below. The blotch is located below the junction between the spinous and soft portion of the dorsal fin. Six to eight blue stripes run horizontally and originate from the head. The upper four stripes end below the soft dorsal and the rest at the caudal peduncle. The blue stripes below the eye are broken between the snout and the opercular margin.
(b) Juveniles of Lutjanus duodecemlineatus
The spinous portion of the dorsal fin has 11-12 spines. A black blotch is present below the soft dorsal. A lateral line runs through the middle portion of the blotch. Six or seven blue stripes are present of which the lower stripes run horizontally and the upper 4 stripes run obliquely from the posterior part of the eye towards the dorsal profile (restricted to the Southeast African coast).
(c) Juveniles of Lutjanus quinquelineatus
A black blotch is present above the lateral line and below the junction between the spinous and soft dorsal fin. Five blue stripes are present horizontally. All the stripes start from the head region and the upper two end below the dorsal fin and the rest end in the caudal peduncle.
4. Salient biological characteristics of important species of lutjanids occurring in the Indo-Pacific mangroves
(a) Maximum size reported from the coastal/coral environment (after Fischer and Whitehead, 1974; Fischer and Bianchi, 1984; Marshall, 1964)
1. Lutjanus johni – 700 mm
2. Lutjanus argentimaculatus – 1200 mm
3. Lutjanus fulviflammus – 425 mm
4. Lutjanus fulvus – 500 mm
5. Lutjanus lemniscatus – 650 mm
6. Lutjanus rivulatus – 650 mm
7. Lutjanus russelli – 400 mm
8. Lutjanus sebae – over 1000 mm
9. Lutjanus vitus – 400 mm
(b) Food and feeding
Almost all the species reported in the section above are carnivores, feeding on fish and crustaceans. Most of these fishes are coral fish using the mangroves as a nursery ground. The juveniles of species numbers 2, 3, 7 and 8 mentioned in the above section feed on penaeid shrimp larvae and juveniles, small crabs, mysids, sergestids, gobioid fish, juveniles of Ambassidae and, rarely, hermit crabs in the Southeast Indian mangrove waters (Jeyaseelan, 1981).
(c) Reproduction
Based on the recruitment of early juveniles and juveniles to the natural stock in the Southeast Indian mangrove nurseries, the following are the spawning seasons of some of the Lutjanids in the coastal/coral environment.
1. Lutjanus johni Single spawning season
October-January
2. Lutjanus argentimaculatus Two spawning seasons
1. October-November
2. May-July
3. Lutjanus fulviflammus Two spawning seasons
1. October-December
2. April
4. Lutjanus russelli Protactile spawner
1. April
2. August
3. December
Year to year variations in spawning activity are not uncommon in many of these species probably due to the success or failure of the northeast and southwest monsoon in this region.
5. Salient ecological information
Among the Lutjanids reported from the mangroves, the juveniles of Lutjanus argentimaculatus, L. johni and L. russelli occur even in highly turbid waters (with a seston content of over 400 g/m^3) (Jeyaseelan, 1981). There is no information about the turbidity tolerance of these species. The juveniles of the three above mentioned species occur even in mixo-mesohaline salinity regimes in the mangrove waters.
About 100 species of Lutjanidae occur in the world oceans of which certain selected species use global mangroves as a nursery ground. Besides the species reported in section 2 above, some other species of the following occur in mangroves of different geographic locations. They include: Lutjanus sanguineus and L. vaigiensis from the South African mangrove estuaries; L. carponotatus from the Australian mangroves; L. apodus, L. jocu and L. griseus from the Atlantic American mangroves and L. agennes, L. eutactus and L. goreensis from the Atlantic African mangroves (Jeyaseelan, 1981).
6. Capture fisheries
Lutjanids are usually caught by hand lines, long lines, traps and bottom trawls. In the mangrove waters, the juveniles and undersized fish are subjected to destructive fishing by cast-nets and drag-nets in the Southeast Indian region (Jeyaseelan, 1981).
7. Culture fisheries
These carnivorous species may become candidate species for coastal and brackish waters (especially in the lower reaches) cage culture in the near future if the following conditions are conducive: a) its acceptability on the international markets, (b) a remunerative price, c) a decline in the quality of fish availability from capture fisheries and its consequence on the demand for culture fish, d) the standardization of hatchling production technology, and e) the availability of fish meal and quality feed (with appreciable FCR) and their influence on the profitability of these carnivorous species.