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Larval Development of King George

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Larval Development of King George Abstract.---The larval develop­ ment of Sillaginodes punctata, Larval development of King George Sillago bassensis, and Sillago schomburgkii is described based on whiting, Sillaginodes punctata, both field-collected and laboratory­ reared material. Larvae of the school whiting, Sillago bassensis, three species can be separated based on a combination ofpigment and yellow fin whiting, and meristic characters, including extent and appearance of dorsal Sillago schomburgkii midline pigment, lateral pigment on the tail, presence or absence of pigment above the notochord tip, (Percoidei: Sillaginidae), from myomere number, extent and tim­ ing of gut coiling, and size at flex­ South Australian waters ion. The most useful meristic char­ acter across the range ofspecimens Barry D. Bruce was number of myomeres. Sillagi­ nodes punctata with 42-45 myo­ South Australian Department of Fisheries meres are easily distinguished GPO Box J625. Adelaide. South Australia 500 J from Sillago schomburgkii with Present address: (SIRO Division of Fisheries. 36-38, and from S. bassensis with GPO Box J538. Hobart. Tasmania. Australia 700 J. 32-35. The timing of gut coiling and its subsequent effect on anus position differed both among the three species examined here and from that previously reported for sillaginid larvae in general. Timing The perciform family Sillaginidae sidered subspecies of S. bassensis of gut coiling and extent of anus (whiting and sand smelts) consists (McKay, 19921. All four species are migration are not useful characters of three genera, three subgenera, widely distributed in southernAus­ for the identification of temperate and thirty-one species of small to tralia and form the basis for impor­ Australian sillaginids at the fam­ moderately sized fishes found pri­ tant commercial fisheries across ily level but are useful on a specific level. Possible implications of the marily in shallow coastal waters of their range (McKay, 1985; Kailola development of the gut to diet are the Indo-Pacific (McKay, 1992). et aI., 1993; May and Maxwel}1). discussed. Sillaginids are highly valued food The adult andjuvenile biology of Based on the presence oflarvae, fishes in many tropical and temper­ each of the four species has previ­ all three species spawn in South ate waters. The Sillaginidae are re­ ously been documented by several Australian waters. No larvae of a fourth sillaginid species, S. flin­ lated to the Percidae, Sciaenidae, authors (Scott, 1954; Gilmour, 1969; dersi, were found during the study. and, to a lesser extent, the Haemu­ Lennanton, 1969; Robertson, 1977; SouthAustralia is the western dis­ lidae (McKay, 1985) although their Weng, 1983, 1986; Burchmore et aI., tributionallimitfor S. flindersi and sister group is yet to be determined 1988;Jones2; Jones et a1.3), but very it does not appear to spawn in the (McKay, 1992). The most speciose of little is known oftheir early life his­ area. the three sillaginid genera (Sillago) tory and neither the eggs nor the includes twenty-nine species. The larvae of any of the four species remaining two genera, Sillaginodes have previously been described. andSillaginopsis, are monotypic. The In 1986, the South Australian taxonomy ofthe family is approach­ Department of Fisheries began an ing stability; only a few species re­ ichthyoplankton program to inves- main undescribed (McKay, 1992). Two genera and thirteen species of sillaginids are found in Austra­ 1 May, J. L., and J. G. H. Maxwell. 1986. Field guide to trawl fish from temperate lian waters. Four species inhabit waters of Australia. CSIRO Division of the waters off South Australia: the "Fisheries Res., Hobart, Tasmania, 492 p. King George or spotted whiting, 2 Jones, G. K. 1979. Biological investigations on the marine scale fishery in South Aus­ Sillaginodes punctata; yellow fin tralia. South Australian Dep. Agric. and whiting, Sillago schomburgkii; Fisheries Rep., 72 p. western school whiting, Sillago 3 Jones, G. K., D. A. Hall, K. L. Hill, andA. bassensis; and eastern school whit­ J. Staniford. 1989. The South Australian marine scale fishery: stoc¥ assessment, Manuscript accepted 15 June 1994. ing, Sillago flindersii. The latter economics, management. SouthAustralian Fishery Bulletin 93:27-43 (1995). two species were, until recently, con- Dep. Fisheries Green Paper, 186 p. 27 28 Fishery Bulletin 93( I). 1995 tigate the larval ecology of commercially important venile colour patterns, after which they are referred fishes ofSouthAustralian waters. An important pre­ to as juveniles. Body length measurements (BL) are requisite ofany such program is the ability to make measured as notochord length, NL (i.e. from the snout an accurate identification of larvae to species. This tip to the end of the notochord), in preflexion and paper details the development of Sillaginodes flexion larvae, and standard length, SL (i.e. from the punctata, Sillago schomburgkii, andS. bassensis lar­ snout tip to the posterior margin of the superior vae collected during this study. hypural elements), in postflexion larvae and juve­ niles. Body depth is taken at two points. Body depth at pectoral (BDp) is equivalent to "body depth" as Materials and methods defined by Leis and Trnski (1989), that is, as "the vertical distance between body margins (exclusive Specimens were obtained from plankton and beach of fins) through the anterior margin of the pectoral seine samples collected between March 1986 and fin base." Body depth at anus lBDa) is defined as the March 1991 aboard the research vessel MRV Ngerin vertical distance between body margins (exclusive in coastal waters and at various inshore nursery ar­ offins and, initially, the gut) through the midpoint eas offSouthAustralia. Details ofsamplinglocations ofthe anal opening. BDa includes the gut only after and procedures are described in Bruce (1989). Briefly, overlying musculature has developed. Sillaginodes larvae were obtained from stepped oblique tows with punctata eggs were measured with a Zeiss photomi­ 70-cm-diameter bongo nets fitted with 500-micron croscope III fitted with an ITC 510 video camera and mesh. Postsettlement (refer to definition below) lar­ linked to an Apple Macintosh SE computer via an vae and juveniles were captured with a fine mesh HEI 582Avideo coordinate digitizer. Egg dimensions beach seine (7 m x 1.8 m, 2-mm mesh) as well as by are reported to the nearest micron. Larvae were dipnetting and diving. The field-collected series of measured to the nearest 0.1 mm with a dissecting Sillaginodes punctata was supplemented with lar­ microscope fitted with an ocular micrometer. vae reared in the laboratory atWest Beach,Adelaide. Postsettlement larvae andjuveniles were measured All field-collected specimens used for description to the nearest 0.1 mm with vernier calipers. were fixed in a 10% formalin-seawater solution buff­ Meristic counts were made on S. punctata and ered with sodium tetraborate (borax) and were later Sillago bassensis specimens cleared and stained with transferred to a 5% solution buffered with sodium alcian blue and alizarin red-S following Potthoff B-glycerophosphate (0.5 g per 1,000 mL). Reared lar­ (1984). Insufficient specimens of S. schomburgkii vae were fixed immediately in the 5% solution. were available for clearing and staining and therefore Reared S. punctata were used for illustration when all meristics were taken from unstained material. possible because of their superior condition. Some Descriptions are based primarily on the detailed pigment differences were apparent between reared examination ofa representative series ofspecimens; and field-collected larvae largely as a result of ex­ however, comments on pigment and meristic vari­ pansion or contraction of melanophores. Melano­ ability stem from the routine examination ofalllar­ phores of field-collected larvae were generally less vae collected. The number ofspecimens examined in expanded thanreared specimens. Reared larvae were detail, the size range covered, and the museum ref­ typically greater in length than similarly developed erence numbers (for lodged material) are provided field-collected material owing to increased shrink­ under each species account. age in the latter. Similar shrinkage effects have been previously reportedfor a varietyofspecies (Theilacker, 1980; Hay, 1981; Bruce, 1988). Unless specified, devel­ Results opment at length refers to field-collected material. Representative series of S. punctata and Sillago Identification bassensis are deposited with the I.S.R. Munro Fish Collection, CSIRO, Hobart Tasmania. Too few S. Larvae were identified to family level from larval schomburgkii larvae were collected to allow a com­ sillaginid characters reported in the literature. Silla­ plete analysis and all are currently held in a collec­ ginid larvae are elongate and have 30-44 myomeres tion maintained by the author at CSIRO Division of (Johnson, 1984; Miskiewicz, 1987; Leis and Trnski, Fisheries, Hobart, Tasmania. 1989). The gut typically reaches to greaterthan 55% Developmental terminology and body measure­ body lengthin preflexion larvae. The anus is reported ments follow Leis and Trnski (1989). The term to migrate anteriorly during development (often dur­ "postsettlement" is used to describe newly settled ing flexion) as a result ofcoiling ofthe anterior sec­ individuals prior to the acquisition ofscales and ju- tion of the gut, thus shortening the preanal length Bruce: Larval development of Sillaginodes punctata, Sillago bassensis, and Sillago schomburgkii 29 (Leis and Trnski, 1989). Sillaginids
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