Fin Fish

Fin Fish

Dr. V. Ramaiyan* and Dr. M. Kalaiselvam

*Professor (Retd.) Centre of Advanced Study in Marine Biology, Annamalai University

ish are cold‐blooded aquatic vertebrates, possessing gills and fins. There are 24,600 species of known fishes (Nelson, 1994), which

comprise almost half the number of total vertebrates. About 95% of fishes are teleosts. Mangrove habitats usually contain a rich ichthyofauna. The mangrove water provide ideal niche for the juvenile fish owing to less water motion, soft substratum, enormous amount of food, excellent shelter and protection from the predatory organisms. Besides, the canopy of mangrove provides a cool, stable and humid environment, quite favourable to the young fishes. The number of finfish species in the mangroves exceeds all other habitats. For the conservation of fishery resources, it is of great importance to have necessary background knowledge on its distribution, seasonal occurrence, biology, biogeography and genetic diversity. Continuing degradation and destruction of mangroves lead to the disappearance of the finfish species associated with the mangroves. In the stupendous task of conservation of mangrove resources in general and finfishes in particular, the present manuscript is prepared on the methodology of finfish collection, preservation and easy identification of mangrove Ichthyofauna.

Methods of Collection

Fishing in mangroves is mainly done by cast net with the help of dugout canoe. Line fishing is also practiced in some areas. Hook and line gear is very ancient and at the same time popular with modern fishermen. Long lines and hand lines are successfully used for collecting large fishes such as tunas, seer fishes, seabass, rays, sharks and catfishes in the sea. Boat seines of several designs are also used for fishing. Boat seines are bag nets of conical shape operated by two canoes or catamarans. Gillnets, seines and drift nets are entangling nets made of nylon or cotton. Gillnets and seine nets could be used for gilling pelagic shoal fishes such as sardines and mackerels in the coastal waters. Shore seines, beach seines or the inshore dragnets are also familiar types of

F

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seines used for coastal fishing including mangrove areas. It does not matter how the fish are caught for taxonomical studies, provided that they are not damaged. Fisherman destroying most of their value as biological specimens breaks off long spined species often having their dangerous spines. Whole individual should be kept wherever feasible.

Preservation of Samples

Formalin is generally a reliable preservative after which they can be transferred to alcohol for lengthy preservation. Commercial formaldehyde (trade name Formalin) is concentrated one (about 40%) and it must be diluted before use.

Large fish need formalin of 10% strength but small fish can be preserved in a more dilute solution. Neutralized formalin is to be preferred because ordinary formalin will soften the bones after some time. Further, specimens measuring more than a few inches in length should have a slit made at the level of the pectoral fin and care must be taken to see that the preservative really enters this slit. Before keeping the specimens in preservative, the median and paired fins must be spread pinned, and concentrated formalin must be applied for fixation.

For storage of specimens after preservation, 70% alcohol is preferred. To transfer the specimens to alcohol, the specimens should be soaked and washed thoroughly in water and transferred to 50% alcohol for a few days before being put into 70% alcohol either for long storage or for packing.

Taxonomical Characters of Fish

Fish display enormous diversity with respect to their biological characteristics and behaviour. In general, morphological characters that are seen externally are the ones used in the identification of fishes. The countable characters of a fish are collectively called as meristic and the measurable characters are called morphometrics. These characters are more superficial as well as more variable and hence they should be employed with caution.

4.1. Meristic Characters (Fig. 1)

Among the meristic characters, scale counts (lateral line scale count, scales above lateral line, scales below lateral line, scales before dorsal fin, cheek scales, circumference scales count, fin ray counts (both spines and soft rays) and vertebrae are the most important. Fin ray formulae used in keys are typically given thus D XIII, 12, A III 15, P 6, V I 6, C 9 (D‐

V. Ramaiyan and M. Kalaiselvam 385

dorsal, A – anal, P – pectoral, v – ventral or pelvic, C – caudal). Sometimes P I is substituted for P and P2 for V.

Fig. 1. Meristic characters in fish.

Spines: True spines are single‐shafted and of entire composition. They are designated by roman numerals, no matter how rudimentary or how flexible they may be.

Soft rays: Soft rays are bilaterally paired and segmented and then are usually not always, branched or flexible. They are designated by Arabic numerals. The last ray of the dorsal and anal fins is often divided at the base making it difficult to decide whether it should be 1 or 2 (it is better to take it as 1 but record it as (+1) to see how it fits in with other people’s keys.

Scale counts: The scales of most fishes have either a smooth exposed surface (cycloid scales) or a minutely denticulated surface (ctenoid scales) which is rough to the feel, the denticulations can be seen with a lens.

Lateral line scale count: This represents the number of pored scales in the lateral or number of scales in the position that would normally be occupied` by such scales. The count is taken from the scale in contact with the shoulder girdle to the structural caudal base the scales wholly on the caudal fin base are not included even when they are well developed or pored.

Scales above lateral line: Unless otherwise stated these are counted from the origin of the dorsal fin (first dorsal fin if two) including the

386 Fin Fish

small scales and counting downward and backward to, but not including the lateral line scales.

Scales below lateral line: These are counted similarly to those above but upward and forward from the origin of anal fin (including the small scales). If continuing upward and forward, the series can be regarded as jogging backward or forward, the backward shifting is accepted. Some authors use scales between pelvic fin and lateral line.

Morphometric Characters (Fig. 2)

Among the morphometric characters, standard length, fork‐length, head length, snout length, post‐orbital length, pre‐dorsal distance, pre‐pelvic distance and pre‐anal distance and gap width (the greatest transverse distance across the mouth opening with mouth opening with mouth closed) are generally considered for identification of fishes. Pointed dividers or dial‐reading calipers should be used for recording the measurements. The measurements aim at comparing the body shape in different species and characters such as the positions of the fins are important. Earlier works generally recorded measurements as proportions e.g. head length 1/3 in standard length, but percentages are now more commonly used e.g. head length as a percentage of standard length.

Fig. 2 Morphometric characters in fish

Standard length: In systematic work this is typically measured as the distance from the anterior tip of the snout or upper lip (whichever extends farthest forward) to the caudal base (junction of hypural bone and caudal fin rays) in a straight line.

Body depth: This is measured at the deepest point exclusive of fleshy or scaly structure at fin base.


Head length: This is measured with the mouth closed from the tip of the snout or upper lip (whichever extends farthest forward) to the posterior edge of the opercular bone.

Snout length: This is measured with dividers from the most anterior point on the orbit and the bony opercular margin.

Postorbital length: This is the greatest distance between the hind margin of the orbit and the bony opercular margin.

Eye diameter: This is generally taken as length of orbit, the greatest distance between the free orbital rims.

Upper jaw length: Lower jaw length is the length of the mandible taken with one tip of the dividers inserted in the posterior mandibular joint to give the maximum possible dimension.

Gape width: This is the greatest transverse distance across the mouth opening with the mouth closed. Gill rackers (lower limb of the first arch), teeth (number of teeth rows, the relative widths and shapes of vomerine and palatine tooth bands), lower pharyngeal teeth, branchiostegal rays, barbells, life colours, osteological features, the structure of the pseudobranchs and the behaviour of fishes are other taxonomic characters used for the identification. These are, however, less commonly used under field conditions.

Procedure for Identification

In order to identify a fish, the first step is to collect the necessary literature such as the keys, checklist and description of the fishes of region. The following procedure is to be followed.

i). Find key characters of fish.

ii). Verify identification with published descriptions, illustrations, etc.

iii). Comparison with identified reference material in the reference collections of the Museums.

iv). If the fish is not comparable with any of the known species, then confirm identification with a specialist to examine the material before describing the fish as new to science.

The old description of new species based on a single specimen has now been abandoned. So long as a species is regarded as a group of identical organisms, which is sharply demarcated from any other group of organisms, the old procedure is adequate. But such a system is not followed when it is conceded that an intraspecific variation exists and

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organisms are in the process of evolution. Our descriptions of species are to be based on a series of adequate material rather than a single type. The morphological characters are still employed frequently than others but new taxonomic characters such as proteins, chromosome, behaviour, ecological conditions, host‐parasitic relations and geographical characters increasingly supplement them.

The modern systematic taxonomic conclusions are, therefore, reached only on the basis of samples from large populations. In order to avoid any bias and to accurately evaluate the taxonomic characters, statistical analyses of populations are sometimes necessary. Often samples of two kinds of fish will differ in respect to the mean value of some count or morphometric measurements. In such case the degree of confidence in the reality of this difference, the variations (standard deviation) of the count both the species and the degree of overlap should be established with the use of highly refined statistical methods. Features used to distinguish the higher categories of genera, families etc., are generally more profound and less variable. Osteological features for example, show little variation and appear to be less subject to environmental influences than vertebrae, scales and fin ray counts. Colour pattern and other aspects of colouration though often of great value as specific characters among the most can be easily recognized and thus the most convenient characters especially among the reef fishes.

Factors Affecting Biodiversity of Fish in Mangrove

Fish populations are declining in many parts of the world at an alarming rate. The decline of fish populations in mangrove ecosystem has occurred due to several reasons, namely: i) habitat modification through conversion of mangrove areas into shrimps/fish farms, ii) aquatic pollution load, iii) over‐exploitation of fish populations, and iv) introduction of certain exotic species/stocks. As a result, the survival of some species has become ‘threatened’. It is estimated that about 1800 fish species in the world are severely threatened. The decline in size and number in the natural fish population has led to loss in genetic diversity, which has far reaching evolutionary consequences. This has been adversely affecting the sustainability of fisheries resources.

The present marine fisheries scenario in India is characterized by declining yields from the inshore waters, increasing conflicts between different resource users, increasing demand for fish food for domestic consumption and export and prospects for large scale sea‐farming and


coastal mariculture. This warrants greater and more effective R&D efforts to enable implementation of suitable marine fisheries and mariculture development. Appropriate conservation measures are to be taken up for judicious exploitation of the existing reserves and to impose precautionary measures to resist overexploitation of rare specimens leading to extinction. Techniques of spawning, rearing, sea ranching and farming are to be adopted to augment existing production of commercially exploited fishes from the Indian coast. Government of Tamil Nadu has implemented ‘closing fishing season’ for 40 days from April to May every year. This is because of the fact that most of the commercially important fishes breed during the 40 days period. Establishment of marine parks, total ban on exploitation of breeding stocks, restriction of professional collection of ornamental fishes, mesh size regulation for commercial exploitation of fishes, and practice of farming techniques are some of the suggestions for conservation and management of fishery resources.

Key for Identification

This key is prepared by compiling most important external, easily recognizable and to some extent internal characters like gill rackers from various books and publications. The photographs, common, English, and FAO names are also given along with species name. This may help in collecting precise species‐specific data to know abundance of particular species during season.

Elops machnata

• Dorsal aspect of the body bluish‐green, flanks silvery; fins yellowish.

• Body elongate and fusiform, with smooth unkeeled body. • Dorsal fin with 20 to 25 soft rays, set near midpoint to body. • Anal fin with 18 to 20 rays, its origin well behind last dorsal‐fin

ray. • Pelvic‐fin base below middle of dorsal‐fin base. • Scales very small, about 100 along lateral line.

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Common Name : Tenpounder

Distribution : Pelagic in coastal waters, entering lagoons and estuaries.

Habit and Habitat : Spawning probably occurs in the sea, the transparent larvae (leptocephali) migrating to inshore nursery areas. Feeds on small fishes and crustaceans.

Stolephorus indicus (Van Hasselt)

• Color of the fish pale cream when scales are lost, bright silvery stripe on flanks.

• Body fusiform, nearly cylindrical, belly rounded, with 3 to 5 needle‐like scutes between pectoral and pelvic fins.

• Snout prominent, rather pointed, maxilla tip pointed, not reaching to anterior border of pre‐operculum, posterior border of pre‐operculum evenly rounded near maxilla tip.

• Dorsal fin with 12 to 13 rays without pre‐dorsal spine.

• Anal fin usually with iii 17 to 20 rays, its origin below dorsal‐fin base.

Common Name : Indian anchovy

Distribution : Throughout the southeast Asia.

Habit and Habitat : Pelagic in coastal waters.

Thryssa setirosis (Brousonet)

• Color of the fish back brown, flanks silvery, fins hyaline.

• Body fusiform, fairly strongly compressed, belly keeled, with 14 to 17 pre‐pelvic and 8 to 10 post‐pelvic scutes.

• Snout fairly prominent, bluntly pointed, maxilla short, extending only a little beyond gill‐opening, not to pectoral‐fin base, mouth strongly oblique.

• Dorsal fin with 10 to 12 branched rays, a small sharp spine before dorsal‐fin and anal fin with 34 to 38 branched rays.


Common Name : Longjaw thryssa

Distribution : East and west coast of India. Also throughout Indonesia to Japan and southward to Sydney, New Calendonia and Fiji.

Habit and Habitat : Pelagic in coastal waters.

Chanos chanos

• Color of the fish back olive‐green, sides silvery, dorsal, anal and caudal fins with dusky margins; inner sides of pectoral and pelvic fins dusky.

• Body torpedo‐shaped; no scutes along belly.

• Mouth small, without teeth, upper jaw slightly projecting, with no supramaxillae, lower jaw with a small symphysial tubercle at tip, fitting into a notch.

• Dorsal fin with 13 to 17 rays, its origin midway between front border of eye and caudal‐fin base.

• Anal fin short, with 9 to 11 rays, close to caudal fin.

• Pectoral and pelvic fins with large axillary scales.

• Caudal fin deeply forked.

Common Name : Milk fish.

Distribution : Throughout whole area. Elsewhere, eastward through Indonesia to Samoa and beyond.

Habit and Habitat : A coastal pelagic species, entering estuaries, rivers and lakes. Feed on bottom invertebrates.

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Mugil cephalus Linnaeus

• Color of the body olive‐green above, silvery on sides, shading into white below; 6 or 7 indistinct longitudinal brown bars down flanks, a dark purple blotch at base of pectoral fin.

• Two widely separated dorsal fins; first fin with 4 spines, second fin with 1 spine and 8 soft rays.

• Anal fin with 3 spines and 8 soft rays.

• Pectoral fins short, not reaching origin of first dorsal fin, with long axillary scale. Caudal fin forked.

Common Name : Flathead mullet

Distribution : Found throughout the area.

Habit and Habitat : A schooling fish entering estuaries and brackish water lagoons, frequently also entering fresh water. Feeds on small algae and other organic matter

Hemiramphus far (Forsskal)

• Color: dark bluish above, silvery white below, with 3 to 9 vertical bars on the sides.

• An elongate fish with a greatly prolonged, beak‐like lower jaw; upper jaw short, triangular and scaleless; preorbital ridge absent.

• Total number of gill rakers on first gill arch 25 to 36.

• Anal fin rays 10 to 12; Pectoral fins short, not reaching past nasal pit when folded forward.


Common name : Black‐barred halfbeak

Distribution : An Indo‐West Pacific species.

Habit and habitat : Found in the proximity of continental coasts and islands, chiefly in areas of rich submerged vegetation. Adults feed mainly on sea grasses, to a lesser extent on green algae and diatoms.

Lates calcarifer (Bloch)

• Color of the fish two phases, either olive‐brown above with silvery sides and belly (usually juveniles) or greenish‐blue above and silvery below.

• Head pointed, with concave dorsal profile becoming convex in front of dorsal fin.

• Operculum with a small spine and serrated flap above origin of lateral line; preopercle with a spine in angle and serrated edge behind.

• Mouth large and slightly oblique, the upper jaw extending to behind eye; teeth villiform in jaws.

• Dorsal fin with 7 to 9 spines and 10 to 11 soft rays; a very deep notch almost dividing spinous from soft‐rayed part of fin.

• Anal fin rounded, with 3 spines and 7 or 8 soft rays.

• Pectoral fin short and rounded.

Common Name : Barramundi

Distribution : Sri Lanka, perhaps extending into Arabian Sea. Also present in the Eastern Indian and the Western Central Pacific.

Habit and Habitat : Found in coastal waters, estuaries and lagoons. Usually occurs at depths of 10 to 40 m. Feed on fishes and crustaceans.

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Epinephlus tauvina (Forsskal)

• Color of the fish ground color of head, body and fins pale brown, with numerous dark green‐brown spots; spots on the fins darker. Caudal fin edged dusky black but with a distinctive fine white outer margin.

• Dorsal fin with 11 spines and 15 or 16 soft rays; anal fin with 3 spines and 8 soft rays and caudal fin truncate or slightly emarginated.

• Preoperculum with convex and finely serrated upper edge with 2 to 4 strong serrae at angle; operculum with a convex upper border and 3 flat spines, the middle spine equipment from upper and lower.

• Maxillary (upper jaw) extending to vertical through posterior edge of eye.

Common Name : Greasy grouper

Distribution : Throughout the tropical Eastern Indian Ocean and the Western Central Pacific to the Pitcairn Islands in the east.

Habit and Habitat : Primarily a coral‐reef species found in depths of 1 to at least 50 m.

Silago sihama (Forsskal)

• Color: back light brown, lower ventral flanks and belly whitish or silvery, without dark blotches.

• First dorsal fin higher than second and with 11 weak spines.

• Anal fin with 2 spines and 21 to 24 soft rays.

• Swimbladder with 2 postcoelomic extensions.


Common name : Silver sillago

Distribution : Throughout most of the area.

Habit and habitat : Inhabits shallow sandy bottoms of shores and bays, also estuaries. Feeds on small invertebrates.

Eletheronema tetratactylum (Shaw)

• Color: body silvery green above; cream below; pectoral filamentous rays white.

• Lips absent, except for lower lip near corner of mouth.

• Eyes large.

• Pectoral fins in 2 parts, upper part with all rays unbranched, lower part with 4 free filamentous rays of which the upper filament is the longest, reaching to pelvic fin base.

Common name : Fourfinger threadfin

Distribution : In the area, from the “Gulf” to the west coast of India and Sri Lanka.

Habit and Habitat : Lives mainly over shallow muddy bottoms in coastal waters, also enters rivers.

Boleophthalmus boddarti (Pallas, 1770)

• Scales are extending forward on the back of the head to the eyes, on the gills covers and the throat; also pectoral fin bases are covered with scales.

• Second dorsal fin uniform in height.

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• Body brownish grey or yellowish brown with irregular coalescent spots and elongate dark brown spots along the mid line.

• A conspicuous black spot on the first dorsal fin.

• Pelvic fins fused by membrane which also extends across the fornt of these fins as a skin fold.

• No lateral line on the sides of the body.

Common name : Mudskipper

Distribution : Marine, brackish, and occasionally freshwater; most tropical and subtropical areas.

Habit and habitat : Inhabit mangrove and mudflat areas

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Fin Fish