Rita macracanthus

biology_ecology

Biology. According to Khan (1934), R. macracanthus (as R. rita) feeds on invertebrates and small fishes. Males have branched and comb-like testes and in the Jhelum River (a tributary of the Indus River), breeding season lasts from June to the end of July, during which the fish migrates to colder waters in shoals.

Rita macracanthus, a new riverine catfish (Teleostei: Bagridae) from South Asia.

description

Description. Morphometric data as given in Table 1. Head slightly depressed; dorsal profile slightly convex posteriorly and ventral profile almost straight. Bony elements of dorsal surface of head covered with thin skin; bones readily visible, ornamented with numerous small tubercles. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit with free margin. Gill openings wide, extending from posttemporal to beyond isthmus. Gill membranes free from isthmus, with 6 branchiostegal rays. First branchial arch with 4 + 9 gill rakers. Mouth subterminal, fleshy upper lip extending anteriorly beyond upper jaw. Oral teeth small, of two kinds, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout, with villiform teeth. Dentary tooth band much narrower than premaxillary tooth band at symphysis, becoming slightly wider before tapering again posterolaterally; teeth on anterior quarter villiform; those on posterior three-quarters bluntly rounded, peg-like. Vomerine tooth patches somewhat elliptical, paired, along lateral margins of palate; teeth on first to sixth anteriormost rows somewhat villiform, those on rest of

Rita macracanthus, a new riverine catfish (Teleostei: Bagridae) from South Asia.

diagnosis

Diagnosis. Rita macracanthus differs from R. chrysea, R. gogra and R. kuturnee in having relatively small eyes (6.9 - 8.7 % HL vs. 14.3 - 29.2) set further apart (interorbital distance 39.4 - 44.1 % HL vs. 28.7 - 37.9). It further differs from R. gogra in having the dorsal surface of the head between the eyes and supraoccipital covered with thin skin (vs. a thick layer of muscle), from R. kuturnee in having moderately elongate vomerine tooth patches with rounded, peg-like teeth (vs. very narrow patches with villiform teeth), from R. chrysea in having a granulated anterior margin of the dorsal spine (vs. middle third with large serrations) and from R. sacerdotum in having a long dorsal spine that reaches to the middle of the adipose fin (vs. short spine not reaching the origin of the adipose fin). Rita macracanthus can also be distinguished from both R. chrysea and R. sacerdotum in having the vomerine teeth in two distinct lateral patches (vs. a single median patch). Rita macracanthus resembles R. rita very closely, but can be distinguished from it in having, in specimens greater than 100 mm SL, a longer dorsal (reaching to middle of adipose-fin base when appressed vs. to origin of

Rita macracanthus, a new riverine catfish (Teleostei: Bagridae) from South Asia.

discussion

Discussion Rita macracanthus and R. rita are very similar-looking species (both species would key out as R. rita using Ferraris, 1999), so the possibility that the differences outlined in this study are solely due to ontogeny must be ruled out. A bivariate analysis (ANCOVA) of the pectoral-spine length, dorsal-spine length and caudal peduncle depth against SL (Fig. 3) shows that the differences are not solely ontogenetic, as the regression lines are significantly different (P <0.00001, P = 0.03706 and P = 0.01658 respectively). The shapes of the tooth plates in catfishes are known to undergo ontogenetic changes, especially those on the palate. In R. rita, as in many other catfishes, the palatal tooth plates tend to fuse along their medial margins in large specimens, giving the appearance of one large median tooth plate. However, the premaxillary tooth plate appears to undergo little ontogenetic change in shape. It was not possible to measure the premaxillary toothplates of all of the specimens of R. rita and R. macracanthus in this study without seriously damaging them (due to the condition they were preserved in), but those for which accurate measurements were possible support the

Rita macracanthus, a new riverine catfish (Teleostei: Bagridae) from South Asia.