Noell: Larval development of Hyporhamphus melanochii and H. regulans 



369 



Materials and methods 



Most larvae were collected with a neuston net in Gulf 

 St, Vincent (34°29'S, ISS'IS'E) and the Bay of Shoals 

 (SS^ST'S, 137"37'E) of South Australia. The neuston net 

 was a square-framed bongo net with a mouth area of 0.5 m-^ 

 fitted with 500-|jm mesh, to which a 30-cm diameter pneu- 

 matic float was attached to both sides of the frame. This 

 attachment ensured that, while being towed, the top of the 

 frame rode steadily above the water surface and that -0.4 

 m^ of the mouth area was submerged. The net was towed 

 from the stern of the vessel inside a circular direction for 5 

 min at speeds of 2-4 knots. Additional larvae were collected 

 by hand from beneath a wharf in Barker Inlet where they 

 often school during daylight at mid-flood tide. Transform- 

 ing larvae and juveniles were collected at night with a 

 dip net and spotlight at Outer Harbor (34°46'S, 138°28'E) 

 and Barker Inlet. The term "transforming" is used here 

 to describe the stage between the end of the larval phase 

 and the start of the juvenile phase, i.e. after the attain- 

 ment of all fin rays and before the formation of scales. All 

 specimens examined in this study were collected between 

 November and March. Larvae were sorted from plankton 

 samples immediately after collection based on reference 

 larval specimens from the South Australian Museum fish 

 collection that were identified to family. Larvae were fixed 

 in 10% formalin buffered with sodium j3-glycerophosphate 

 ( 1 g/L) and later preserved in 70% ethanol. 



A total of 47 H. melanochir (6.4—48.3 mm body length, 

 BL) and 49 H. regularis (7.0-46.9 mm BL) larvae through 

 juveniles were used to describe morphometries, meristics, 

 and pigmentation. Larvae were identified as hemiram- 

 phids based on larval and adult characters reported in the 

 literature (Collette, 1974; Hardy, 1978; Collette et al., 1984; 

 Chen, 1988; Watson, 1996; Trnski et al., 2000). Develop- 

 mental series were assembled by using the series method 

 (Neira et al., 1998), the accuracy of which was verified by 

 a molecular technique (Noell et al., 2001). Terminology of 

 early life history stages follows that of Kendall et al. ( 1984). 

 Representative series for both species are deposited with 

 the I.S.R. Munro Fish Collection (CSIRO, Hobart, Tas.). 

 (Registration numbers: H. melanochir (n = 13), CSIRO L 

 3072-01, 3073-01 to -08, 3074-01 to -02, 3075-01 to -02; H. 

 regulans (n=12), CSIRO L 3076-01 to -07, 3077-01 to -02, 

 3078-01 to -03.) 



Larvae were examined with a Wild M3Z stereomicro- 

 scope at 6.5-40x magnifications by using various com- 

 binations of incident and transmitted light. Body mea- 

 surements were taken with SigmaScan Pro® 4.01 image 

 measurement software (SPSS Inc., 1999) and are accurate 

 to less than 0.05 mm. This method was particularly useful 

 for measuring cumulative distances of bent larvae. Abbre- 

 viations and definitions of routinely taken body measure- 

 ments follow Leis and Carson-Ewart (2000). Lower jaw 

 length (LJ) is defined as the horizontal distance from the 

 tip of the lower jaw to the anterior margin of the pigmented 

 region of the eye. Lower jaw extension (LJx) is defined as 

 the horizontal distance from the tip of the lower jaw to 

 the tip of the snout. Eye diameter was measured along 

 both horizontal (EDh) and vertical midlines (EDv) of its 



pigmented region. Body depth was measured at two points: 

 at the pectoral base (BDp) and at the anus (BDa). Other 

 measurements taken were snout length (SnL), head length 

 (HL), pre dorsal-fin length (PDL) and preanal length (PAL). 

 All measurements are expressed as a percentage of BL. 

 Pigment refers to melanin. Drawings were prepared with 

 the aid of a camera lucida. 



Selected specimens were cleared and stained with alcian 

 blue and alizarin red-S, following the method of Potthoff 

 ( 1984), in order to count fin rays and vertebrae. Myomeres 

 were difficult to count reliably at either end and thus 

 vertebral counts (which include the urostyle) of stained 

 larvae were taken instead. For small larvae that had un- 

 formed centra, corresponding neural or haemal spines were 

 counted to obtain the number of vertebrae. 



Results 



Southern sea garfish (Hyporhamphus melanochir 

 Valenciennes, 1846) (Fig. 1 ) 



Description of larvae The smallest H. melanochir larva 

 examined was a 6.4-mm newly hatched, laboratory-reared, 

 postflexion-stage specimen. Some yolk remained, although 

 yolk absorption was complete in the smallest field-collected 

 larva (6.9 mm). 



Larvae are elongate to very elongate (BDp=7-13% BL), 

 and have a body depth slightly tapered towards the anus 

 (BDa= 7-9% BL). Relative body depth at the pectoral base 

 decreases slightly during larval development (Table 1). 

 Larvae have 58-61 vertebrae (Table 2). The gut is relatively 

 thick, long, straight, and nonstriated. PDL and PAL remain 

 in the ranges of 70-75% and 71-76% BL, respectively (ex- 

 cept for the 17.0-mm larva, which had a PDL and PAL of 

 62% BL). The first dorsal-fin ray is slightly anterior to or di- 

 rectly above the corresponding anal-fin ray. There is no gap 

 between the anus and the anal fin. A long preanal finfold, 

 initially the same length as the gut, persists through to 

 the transformation stage before it disappears. There is no 

 head spination. The small to moderate head (HL= 16-24% 

 BL) decreases in size in relation to BL with larval growth 

 (Table D.The longer lower jaw protrudes beyond the snout 

 (LJx) by 4% BL at 11.0-11.5 mm, increasing to a maximum 

 of 34% BL in the 29. 3-mm juvenile. The mouth is oblique 

 and reaches to the level of the center of the eye in newly 

 hatched larvae. The maxilla subsequently moves forward 

 in relation to the eye and by 12.1-14.4 mm it does not reach 

 the eye. Very small villiform teeth are present on both the 

 premaxilla and dentary in newly hatched larvae. The mod- 

 erate to large eye (EDh=6-109} BL or 33-42% HL) is elon- 

 gate (EDv=78-88% EDh) and decreases in size in relation 

 to BL. A single rudimentary nasal papilla first appears as 

 a small fleshy lump in the olfactory pit by 17.0 mm. Scales 

 first appear between 20.4 and 29.3 mm laterally on the tail, 

 anterior to the caudal peduncle. 



Development of fins Completion of fin development in H. 

 melanochir occurs in the following sequence: C — ► D — ► A 

 -* Pj, P2 (Table 2). All principal rays of the caudal fin (7-1-8) 



