ICHTHYOLOGICAL BULLETIN of the J. L. B. SMITH INSTITUTE OF ICHTHYOLOGY RHODES UNIVERSITY, GRAHAMSTOWN NUMBER 36 SEPTEMBER 1977 A TAXONOMIC STUDY OF THE GENUS LETHRINOPS REGAN (PISCES: CICHLIDAE) FROM LAKE MALAWI PART 1 by DA VID H. ECCLES and DIG BY S.C. LEWIS Ministry of Agriculture and Natural Resources Fisheries Department, Fisheries Research Station, P.O. Box 27, Monkey Bay, Malawi. I.S.B.N. 949980854 A TAXONOMIC STUDY OF THE GENUS LETHRINOPS REGAN (PISCES: CICHLIDAE) FROM LAKE MALAWI - PART 1 by DAVID H. ECCLES 1 AND DIGBY S.C. LEWIS 2 ABSTRACT Haplochromis micrentodon Regan is transferred to the genus Lethrinops and redescribed. Two new species of Lethrinops which, like the above, are characterised by the possession of lower pharyngeal bones bearing close pavements of slender blunt-tipped teeth are described. 1 Senior Fisheries Research Officer, Fisheries Research Station, P .0. Box 27, Monkey Bay, Malawi. 2 Fisheries Research Officer, Fisheries Research Station, P.O. Box 27, Monkey Bay, Malawi. RHODES UNIVERSITY PRESS GRAHAIIISTOWN CONTENTS Introduction . ...... Notes on characters Abbreviations . 2 I Lethrinops micrentodon (Regan 1921) . 2 Lethrinops stridei n. sp. 4 Lethrinops microdon n. sp. 7 Discussion . 11 IKTRODUCTION such group which consists of three species characterised by the possession of a Lower pharyngeal bone similar to The genus Lethrinops, which is endemic to Lake that of Sarotherodon Riippell, with a heart-shaped Malawi, was established by Regan in 1921 to accommo­ dentigerous region of densely crowded, slender, blunt­ date four species which differed in dentition from mem­ tipped teeth. One of the three has been described pre­ bers of the genus Haplochromis. The genus was characte­ viously as a member of the genus Haplochromis rised by the possession of a few series of very small Hilgendorf and the other two are new to science. slender teeth formed into narrow bands which are interrupted at the symphysis, the teeth in the outer row NOTES ON CHARACTERS: being mostly bicuspid anteriorly and single cusped posteriorly, and those in the inner row unicuspid or tri­ Measurements were made with vernier calipers cuspid. reading to O.lmm. Length values were obtained by Ahl (1927) described three new species which he placing the fish on a measuring board with the head assigned to Lethrinops, and Trewavas (1931), as a result touching the head block and the axis of the body at of examining the large collection of Malawian fishes right angles to the block, and measuring the perpendicu­ made by Christy in 1925-26 and re-examining the lar distance from the block to the appropriate point. original material of Regan and Ahl, revised the genus and Projected measurements of this type are readily repro­ increased the number of component species to 23. ducible and can be directly compared with figures since Trewavas also expanded the definition of the genus so no parallax is involved. Head length is taken as the dis­ that it might be more clearly segregated from tance from the tip of the longer jaw to the posterior Haplochromis. The most important additional distin­ margin of the bony operculum, snout length as the pro­ guishing factor that she noted was the characteristic jected distance from the tip of the upper jaw to the pattern of dentition in the lower jaw of Lethrinops anterior border of the orbit, eye diameter as the distance species. In the genus Haplochromis the outer row of between the anterior and posterior points on the cartila­ teeth in the lower jaw extend backwards beyond the ginous border of the orbit. Total length is measured with posterior limit of the inner teeth to form a single row the tail closed so that the outer rays are parallel to the which often runs almost to the angle of the mouth. In axis. All dorsal and anal spines and rays are measured Lethrinops the outer row of teeth in the lower jaw along their posterior border. The length of the pectoral curves abruptly inwards just behind the most posterior is taken from the upper part of the axilla and that of the teeth of the inner rows to end at some distance from the pelvic spine and fm from the point of articulation of the angle of the mouth, and the teeth are not continued spine. backwards as a single series in any of the species she The degree of emargination of the caudal is indicated studied. The present work shows that in some individuals by the ratio between the lengths of the longest and of some species of Lethrinops, including£. micrentodon, shortest rays, measured from the end of the caudal there is a short series of 1-4 teeth behind the end of the peduncle to the ends of the respective rays. In many outer row but these continue the line of the inner row individuals the last rays of the dorsal and anal fins are rather than the outer as in Haplochromis. very close together and there is doubt, without X-ray The establishment of a programme of exploratory examination, whether they arise from one or two trawling in Lake Malawi by the Fisheries Research Unit actinosts. Such instances are indicated by showing both of the Malawi Department of Fisheries in the 1960's possible counts, the higher in parentheses. brought to light many hitherto unknown cichlid species, In addition to the character of the teeth on the lower a number of which can be included in the genus pharyngeal bones, the proportions of these bones are Lethrinops. The acquisition of large quantities of often useful diagnostic characters in the Cichlidae of material from many parts of the lake has also enabled a Lake Malawi. The measurements used are: pharyngeal re-evaluation to be made of the status of, and range of fork length, the length along the median suture; pharyn­ morphological variation exhibited by many of the pre­ geal total length, the projected length from the anterior viously described species. One of us (D. H. E.) has tip to the line joining the most posterior parts of the examined the type specimens of all the described species bone; pharyngeal width, width across the muscular of Lethrinops and compared them with more recently processes; pharyngeal depth, the greatest depth of the captured specimens. As the genus as a whole has attained bone including its attached teeth; blade length, the very considerable economic importance since the deve­ distance from the tip of the blade to the anterior tip of lopment of a commercial trawling industry of Lake the toothed portion; blade depth, the greatest depth Malawi, it has become more than ever necessary to up­ measured transverse to the axis of the blade. date the somewhat confused classification of this group. The total number of pored scales in both the upper Within the genus are a number of more or less well and lower lateral lines is co1,mted, with the exception of defined groups which may be separated on such charac­ any on the lower line which occur posterior to the arti­ ters as body and head shape, pharyngeal dentition and culation of the hypural plate. The degree of overlap of number and form of gill-rakers. This paper examines one the lines varies between individuals, and even between 1 the sides of one individual, and tends to be greater in USNM - United States National Museum those species from deeper water. The number o( scales MFRU - Malawi Fishery Research Unit in a longitudinal series is derived by the same method as MACT - Musee de l'Afrique centrale, Tervuren that used by Trewavas (1935). From the end of the upper lateral line one proceeds to the scale of the lower Lethrinops micrentodon (Regan, 1921) (Fig. 1) lateral line next behind the transverse row that includes Haplochromis micrentodon Regan, 1921: 715, fig. 27; the last scale of the upper lateral line and slopes down­ Trewavas 1935: 108; Jackson, 1961: 567; Jackson et al., wards and forwards from it. The number of scales 1963: 83. between the first dorsal spine and the upper lateral line is counted along the transverse series sloping backwards DIAGNOSIS from the base of the spine, and does not include the pored scale. Cheek scales are counted as series below the A moderate sized species attaining a standard length orbit. of about 120mm and resembling L. stridei and L. Gill-rakers are counted on the outer edge of the microdon in the possession of a broad lower pharyngeal anterior arch. In most individuals one gill-raker is bone bearing a pavement of small, densely crowded, attached to the region of the articulation of the epi­ blunt-crowned teeth showing little gradation in size. branchial and the ceratobranchial and cannot be assigned Differs from these species in the possession of fewer gill­ to either section. Three figures are therefore shown, for rakers on the ceratobranchial (15-19) and in the pre­ the epibranchial, the articulation and the ceratobranchial. sence of an indistinct dark blotch on the flank, and from In most African cichlids the distal part of the mem­ L. microdon in the possession of a lower jaw shorter brane of the spinous part of the dorsal ftn forms angular than the upper and in the presence of 8 to 9 dark bars lappets which are supported by the spine anterior to on the flank as compared with 7 in that species. Pecto­ them but are free posteriorly. The colour of these is rals in females and non-breeding males not extending often a valuable diagnostic character in living specimens. further backwards than base of third anal ray. MATERIAL EXAMINED ABBREVIATIONS Measurements based on 23 specimens including 2 un­ Abbreviations used for collections or institutions are as sexed, 92 and 116mm, 12 males, 92-119mm and 9 follows:- females 96--118mm S.L.