Bruce Larval development of Sillagmodes punctata. Sillago bassensis, and Sillago schomburgku 



29 



(Leis and Trnski, 1989). Sillaginids have a charac- 

 teristic series of melanophores along the dorsal and 

 ventral midlines (particularly prominent in small 

 larvae) and generally have pigment located on the 

 angle of the lower jaw. 



Three types of sillaginid larvae were found during 

 this study. Specific identity of two of the types (S. 

 schomburgkii and Sillaginodes punctata) was estab- 

 lished by comparing vertebral counts and fin 

 meristics of postflexion larvae to those of adult and 

 juvenile specimens. Smaller larvae were linked by 

 establishing a developmental series based on the 

 extent and appearance of dorsal midline pigment, 

 lateral pigment on the tail, presence or absence of 

 pigment above the notochord tip, myomere number, 

 extent and timing of gut coiling, and size at flexion. 

 The identity of S. punctata was also confirmed by 

 comparison to reared larvae. 



Though clearly separating Sillaginodes punctata 

 from Sillago schomburgkii, fin meristics and verte- 

 bral counts overlap in the other two South Austra- 

 lian sillaginid species (S. bassensis and S. flindersi), 

 thus making the specific separation of their larvae 

 difficult. Sillaginid larvae from southern Tasmania 

 (where only S. flindersi are found) and larvae be- 

 lieved to be S. flindersi from New South Wales (NSW) 

 coastal waters were compared to the third sillaginid 

 larval type collected in South Australia in order to 

 ascertain its identity. The NSW and Tasmanian (re- 

 ferred to herein as eastern) specimens were highly 

 similar but differed from the South Australian type 

 with respect to two pigment characters. First, east- 

 ern specimens had a single prominent, elongate mel- 

 anophore located below the level of the pectoral fin 

 base and overlying the cleithrum that was absent in 

 South Australian material (Fig. 1). Second, eastern 

 specimens developed external lateral midline pig- 

 ment on the tail at an earlier size (7.2 mm) than did 

 South Australian material (14.8 mm). Two sillaginids 

 are known from Tasmanian waters: Sillaginodes 

 punctata and Sillago flindersi (Lastetal., 1983). Only 

 S. flindersi is known to spawn in Tasmanian waters. 

 The eastern form was thus identified as S. flindersi 

 and the South Australian specimens as S. bassensis. 

 Insufficient material was available across the full size 

 range to render an adequate description of the lar- 

 val development of S. flindersii, and thus this spe- 

 cies is not treated in further detail here. 



The most useful meristic character separating the 

 three South Australian larval types was number of 

 myomeres. Sillaginodes punctata with 42-45 

 myomeres are easily distinguished from Sillago 

 schomburgkii with 36—38 and S. bassensis with 32— 

 35. Meristic details for these three species and S. 

 flindersi are listed in Table 1. 



Descriptions 



King George whiting [Sillaginodes punctata 

 Cuvier 1829), Figure 2 



Material examined — 75 specimens, 2.0-30.5 mm 

 BL (CSIRO L587-01, L587-02, L587-03, L587-04, 

 L587-05, L587-06; L588-01; L589-01). 



Larval development — The pelagic eggs of S. 

 punctata are spherical and have an unsegmented 

 yolk and smooth chorion. Late stage eggs are 839- 

 935 microns in diameter (mean 880, n=25) and have 

 a single oil droplet 246-263 microns in diameter 

 (mean 255, n=25). Reared larvae hatched at 2.00- 

 2.15 mm (mean 2.07, re=24) at 16.5-18.7°C. The tim- 

 ing of fertilization was not recorded as spawning oc- 

 curred in brood stock tanks overnight. Estimates for 

 incubation period are 48-60 hours. The temperature 

 of the spawning tank was 16.5°C and fertilized eggs 

 were transferred to a 90-liter tank held at 18.0-18.7°C 

 for subsequent incubation, 24 hours prior to hatching. 



Newly hatched larvae have a posteriorly located 

 oil droplet and adopt a head-down position in rear- 

 ing containers. Yolk absorption was complete in 

 reared larvae by 3.5 mm (8 days), although the small- 



Figure 1 



Detail of head and trunk pigment of (A) Sillago bassensis 

 and (B) Sillago flindersi. Myomeres have been omitted for 

 clarity. Position of cleithrum is indicated by a dotted line. 

 Arrow indicates characteristic melanophore overlying 

 cleithrum in S. flindersi. 



