The description of Austroglossus pectoralis ( Teleostei : Soleidae ) larvae from the South-east coast of South Africa *

The family Soleidae comprises two subfamilies, the Achirinae and Soleinae (Ahlstrom et al., 1984), with the majority of described larvae world wide belonging to the Soleinae. In southern African waters, the family Soleidae comprises twelve genera and sixteen species (Heemstra and Gon, 1986) all within the subfamily Soleinae. The genus Austroglossus is represented by only two species, A. microlepis and A. pectoralis, both of which are endemic to southern Africa and of some importance to the commercial trawl fishery. The eggs and larvae of A. microlepis have been described in detail (O’Toole, 1977; Brownell, 1979), but the early stages of A. pectoralis have not yet received attention. Between 1993 and 1996 along the south-east coast of South Africa, spring appeared to be the peak season for larval abundance, followed by summer and autumn (Wood, 1998). Unpublished data from Marine and Coastal Management (MCM) in Cape Town has shown that peak reproductive activity is between April and October (Frances Le Clus, MCM, pers. comm.). Evidence from captive specimens pointed to a year round spawning capability (Le Clus et al., 1994) which supported earlier field observations by Zoutendyk (1974), Hecht (1976) and Payne (1986 in Le Clus et al., 1994). While SCI. MAR., 64 (4): 387-392 SCIENTIA MARINA 2000


INTRODUCTION
The family Soleidae comprises two subfamilies, the Achirinae and Soleinae (Ahlstrom et al., 1984), with the majority of described larvae world wide belonging to the Soleinae.In southern African waters, the family Soleidae comprises twelve genera and sixteen species (Heemstra and Gon, 1986) all within the subfamily Soleinae.The genus Austroglossus is represented by only two species, A. microlepis and A. pectoralis, both of which are endemic to southern Africa and of some importance to the commercial trawl fishery.The eggs and larvae of A. microlepis have been described in detail (O'Toole, 1977;Brownell, 1979), but the early stages of A. pectoralis have not yet received attention.Between 1993 and 1996 along the south-east coast of South Africa, spring appeared to be the peak season for larval abundance, followed by summer and autumn (Wood, 1998).Unpublished data from Marine and Coastal Management (MCM) in Cape Town has shown that peak reproductive activity is between April and October (Frances Le Clus, MCM, pers. comm.).Evidence from captive specimens pointed to a year round spawning capability (Le Clus et al., 1994) which supported earlier field observations by Zoutendyk (1974), Hecht (1976) and Payne (1986in Le Clus et al., 1994) The description of Austroglossus pectoralis (Teleostei: Soleidae) larvae from the South-east coast of South Africa* adults are found in waters between 10 and 120 metres (Heemstra and Gon 1986), they appear to spawn between Cape Agulhas and Port Alfred in waters between 50 and 108 metres over a mud or sandy seabed (Le Clus et al., 1994).Eggs are probably released off the bottom above the nepheloid layer which covers mud patches.Six other soleid species which are found in southern African waters have had aspects of their early life histories published.These are A. microlepis (O'Toole, 1977;Brownell, 1979), Dicologlossa cuneata (Lagardère and Aboussouan, 1981), Heteromycteris capensis (Brownell, 1979), Monochirus luteus (Nichols, 1976 in Olivar andFortuño, 1991), M. ocellatus (Palomera andRubiès, 1977 in Olivar andFortuño, 1991), Pegusa lascaris (Clarke, 1914in Ahlstrom et al., 1984;Russell, 1976) and Synapturichthys kleini (Brownell, 1979).This paper provides a description of the preflexion and flexion larval stages of A. pectoralis which were sampled from the Tsitsikamma National Park along the south-east coast of South Africa.

MATERIAL AND METHODS
The Tsitsikamma National Park is a Marine Protected Area along South Africa's south-east coast and extends from Oubosstrand (34 o 03'S, 24 o 11'E) in the east to Grootbank (34º00'S, 23º30'E) in the west.The larval description is based on 22 larvae (1.6-8.8 mm BL) identified from samples collected in this area using bongo nets and an RMT1x6 multiple level sampler between August 1993 and October 1996.Specimens were fixed in 5% buffered formalin in sea water then transferred to 70% ethanol after two weeks.Eight larvae that were cleared and stained for morphological features were stored in 95% ethanol before being processed according to the methods of Pothoff (1984).Larvae were drawn facing right with the aid of a camera lucida attached to a dissecting microscope.Larval measurements to the nearest 0.01 mm were performed using a dissecting microscope and an ocular micrometer.Terminology follows that of Leis and Trnski (1989).The following body measurements were made, body depth (BD), body length (BL), eye diameter (ED), head length (HL), pre-anal length (PAL), pre-dorsal fin length (PDL), and snouth length (SnL).
All specimens used for this description have been accessioned into the collection at the J.L.B.Smith Institute of Ichthyology in Grahamstown, South Africa (RUSI numbers 57400-57444).

RESULTS
Description is based on nine larvae ranging in size from 1.6 mm to 8.8 mm BL (Fig. 1).Larvae are moderately elongate, laterally compressed and bilaterally symmetrical (due to the absence of eye migration) They are moderately deep bodied (BD ranges from 0.32 to 051% BL -Table 1), the gut however, is massive and protrudes well below the ventral margin of the body.The smallest larva (1.6 mm BL) possessed a yolk-sac with a single pigmented oil globule, with those < 2.9 mm BL still displaying remnants of yolk.The coiled gut extends to 52% BL in preflexion larvae and 42% BL in flexion larvae (Table 1).A gas bladder was only visible in one of the preflexion specimens measuring 4.0 mm BL.The head is moderately large, ranging from 0.18 to 0.41% BL in preflexion larvae and 0.24 to 0.28% BL in flexion larvae (Table 1), with a steep profile during initial stages and a more gradual convex profile in later stages.In preflexion larvae the mouth does not reach the anterior margin of the eye, but it becomes relatively larger during flexion, eventually reaching the posterior margin of the eye in the largest specimens.Small, robust teeth are visible in larvae from 4.0 mm BL, with those in the lower jaw becoming elongate and incisor-shaped in flexion larvae >5.4 mm BL.The eye is small and round ranging in size from 0.02 to 0.05% BL (Table 1), and there was no evidence of eye migration in the largest (8.8 mm BL) specimen examined.Pectoral fins are visible from the yolk-sac stages (<2.9mm BL) but no rays develop even in the largest specimen.The caudal fin anlage is the fist to appear, followed by the dorsal and anal anlagen.Large flexion larvae had a percentage of fully developed caudal fin rays, and while ossification was not yet complete an 8.67 mm BL larva has a fin count of D92 and A86 which is in agreement with the meristic values for for adult fish.A translucent zone develops ventrally and dorsally to the body musculature in late flexion larvae and houses the elongate pterygiophores.
Vertebrae and myomere counts were not possible for the smaller preflexion larvae examined, with only eight preanal myomeres visible in some.By 4.0 mm BL, however, a total of 50 myomeres (10 + 40) and 52 vertebrae were visible.In flexion specimens, the full compliment of 58 vertebrae were visible, and myomeres ranged from 56 to 58 (8-9 + 47-49) in flexion specimens.Flexion in this species is evident in some 3.5 mm BL larvae, and in all those >3.8 mm BL.
Pigment (Fig. 1 ).Myomeres at the yolk-sac stage were not distinct and only pre-anal elements have been illustrated.Similarly, vertebrae have not been illustrated but numbers do appear in Table 2.

A D C B
pigmentation was somewhat reduced in the larger specimens.Preflexion larvae also posses some internal coverage over the hindbrain region.The angle of the lower jaw is heavily marked during all stages while the region beneath the lower jaw bears fine pigment in preflexion stages which develop into larger melanophores during flexion.Isolated patches are evident on the subopercular and opercular surfaces, and a few small pigment clusters are visible at the base of the pectoral fin bud at 4.0 mm BL.During all stages, the ventral and lateral surfaces of the gut are extensively covered by large stellate melanophores interspersed with numerous clusters of small spots.The oil globule situated on the ventral gut surface in yolk-sac larvae is covered by small pigment spots.Scattered internal pigment is visible over the dorsal gut region in preflexion stages in the vicinity of the gas bladder, while flexion larvae bear a few large stellar melanophores in this region.The ventral midline of the tail in yolksac larvae bears 18 large melanophores packed closely together in a longitudinal series which extends to just short of the notochord tip.Arising from some of these melanophores are branches of pigment which intrude onto the lateral surface of the tail.Large preflexion specimens still have extensive ventral tail pigment, although only seven large patches were evident with the rest of the surface covered by closely packed spots.Between 15 and 17 large melanophores mark the ventral line of the tail during flexion stages, some of which have branches stretching onto the ventro-lateral surface.Eleven large melanophores mark the dorsal midline of the trunk and tail in yolk-sac larvae, with some overlapping onto the finfold and some sending out branches onto the lateral surface.Three smaller melanophores are arranged over the notochord tip.Larger preflexion specimens bear 14 evenly spaced melanophores and flexion stages posses twelve to fourteen medium to large melanophores which straddle the dorsal midline of the trunk and tail, with the spacing between them increasing with larval size so that they extend almost to the notochord tip in late flexion larvae.Some of these melanophores overlap onto the dorsal translucent zone and the dorso-ventral surface.The small melanophores near the notochord tip in preflexion specimens have been lost by the time notochord flexion is initiated.A single medium-sized stellar melanophore is situated medio-laterally on the 11th postanal myoseptum in larger flexion stages.The dorsal and ventral primordial finfolds in preflexion stages are extensively covered by numerous small pigment spots which persist during flexion stages and are manifested on the fin membranes and over the translucent zones which house the pterygiophores.

DISCUSSION
According to Leis and Trnski (1989) the suite of characters which is used to describe soleid larvae is unique amongst the flatfishes, and as such they are not susceptible to misidentification as belonging to one of the other pleuronectiform families.Amongst these characters are the absence of elongate fin rays, a convex head profile, no head spination, large gut, small eyes, a pectoral fin which is not paddle-shaped and which is retained through metamorphosis, and paired pelvic fins.The development of A. pectoralis is similar to that of other members of the Soleinae in certain aspects, where for example the size at hatching and size of yolk-sac larvae range from 1.3 mm BL for D. cuneata (Lagardère and Aboussouan, 1981) to 4.1 mm BL for Aesopia cornuta (Mito, 1963).This study revealed yolk-sac larvae measured between 1.6 and 2.9 mm BL.It is difficult to compare other aspects of development such as flexion, as the size at which this occurs amongst the Soleinae is highly variable.Flexion occurs in A. microlepis and D. cuneata between 5.2 and 5.5 mm BL and 6.3 and 6.5 mm BL respectively (O'Toole, 1977;Lagardère and Aboussouan, 1981) compared with the small size of 3.5 mm BL observed for A. pectoralis (Table 2).
The most obvious differences between A. pectoralis larvae and those of the seven other soleid species from southern African waters which have been described appear in Table 2.These encompass vertebral and myomere counts, size at flexion and pigment patterns.The most closely related species, A. microlepis, not only possesses different morphological and pigmentation patterns but its distribution is restricted along the west coast and as far as False Bay (Heemstra and Gon 1986), whereas A. pectoralis is distributed from the Cape all along the east coast to Natal.According to Heemstra and Gon (1986) there are 16 soleid species found in southern African waters, but of these only five are found on the south-east coast within the vicinity of the study area.The remainder are restricted either to the west coat or the KwaZulu-Natal coast in the north.Three of the species which are found in the study region and whose larvae have not been described, namely Solea bleekeri, Solea fulvomarginata and Synaptura marginata, could not be confused with A. pectoralis as they possess 32-37, 41-43 and 46 vertebrae resprectively (Heemstra and Gon, 1986) as opposed to the 58 for A. pectoralis.

TABLE 1 .
-Morphometrics for Austroglossus pectoralis larvae sampled from the Tsitsikamma coast, measured as a percentage of body length.

TABLE 2 .
-A summary of the common descriptive features for larvae of the eight soleid species which have been described and which are found in southern African waters (* denotes size at completion of flexion, the rest are size at commencement of flexion).