Taxonomy of Finfish

2.1.6.2 Unpaired fins

The dorsal, anal and caudal fins are unpaired in the sense that they are single and not in pairs as the above. The dorsal fin in most fishes is single, concave in shape (Fig. 26 A) with smooth or serrated spine (Fig. 26 B), with simple (Fig. 26 D), and branched rays (Fig. 26 F). The principal ray may be thickened (Fig. 26 E). There may be a procumbent spine in some (Fig, 26 G Mystacoleucus). In Megalops cyprinoides the last ray is prolonged as a filament (Fig. 26 H). In Perches there are two dorsal fins one after the other with the first one separated either by a short or long gap from the second fin (Fig. 27 B) or may even be united (Fig. 27 A); both may bear spines and also soft and branched rays. Generally the first fin is shorter than the second one but this may not always be true. In mugils the first fin is with spines only, separated from the second one by adistance. In Synbrachids (Swamp eels) the dorsal fin is vestigial in the form of ridges only. In Mastacembelus the fin is in two parts; the first one with 32 to 40 short depressible spines and 46 to 90 rays. In Sillaginopsis the second dorsal spine is prolonged as a long filament(Fig. 26 C). The fin may be in different positions on the dorsal profile, mostly at the center, but in many may be far posterior above the anal fin. The fin may be free or even confluent with the caudal fin.

Fig 26 & 27 Added

An adipose dorsal fin is present in siluroids and salmons; it is generally smooth, free (Fig. 28A) and not united with the rayed dorsal fin though the interspace between the two may be long or short. In Sisor rhabdophorus the adipose fin is reduced in the form of a spine (Fig. 28 C). In Chaca chaca and some other fishes it is confluent with the caudal fin (Fig. 28 B).

Figure 28 Added

The anal fin is inserted on the ventral side and is with simple and branched rays. Generally the fin is free (Fig. 29 A), short, but exceptions are there as in the case of Horabagrus, Clarias, Heteropneustes, Schilbeids, Pangasids. Plotosids. In the latter the fin is confluent with the caudal fin. (Fig. 29 B); whereas in Claridae and Heteropneustidae though long, it is separated from the fin by a short distance. In Horaichthys the fin is modified into two parts; the first six rays are separated as an independent gonopodium. In Garnbusiaan intromittant organ i~present (Fig. 29 D). In both cases Onlythe males show this adaptation. The perches (Fig. 29 C Dah1ioides quadrifasciatus)may have spines in the anal fin.

Fig 29 Added

The caudal fin or the tail fin is the propeller for the fish and acts as a rudder. It is the posterior most part of the fish body. It is of varying shapes and is always a single fin, rounded. with or without margins (Fig. 30 C), truncate (Fig. 30 F), furcate or slightly emarginate (Fig. 30 A), forked (Fig.30 B), lunate or lanceolate (Fig. 30 H), wedge or paddle shaped (Fig. 30 D), notched (Fig. 30 E), rounded (Fig. 30 G) or ovate (Fig. 30 J) etc. In most cases it is forked to varying degrees. The lobes may be equal or unequal (Fig. 30 K) and sometimes filamentous extensions are also present (Sisor, Bagarius).

Fig 30 Added