78 



Fishery Bulletin 91(1), 1993 



Figure 1 



Distribution of trachichthyid larvae sampled in southeast Aus- 

 tralian waters. (•) Paratrachichthys sp., (*) Optivus sp., ( ) 

 Aulotrachichthys sp. 



the former of striated silvery tissue on the bases of the 

 pectoral fin, on the isthmus beneath the gill cover, and 

 in a narrow strip along the ventral edge of the body 

 (May & Maxwell 1986). However, examination of juve- 

 nile and adult specimens also reveals a difference in 

 anal fin-ray counts: Paratrachichthys with a count of 



111,10 and Aulotrachichthys with 111,8. Both series had 

 a pelvic count of 1,6. An anal count of 111,8 and stri- 

 ated pectoral tissue occurred in the largest specimen 

 of only one series; on that basis, we assign the series 

 with the largest specimen to Aulotrachichthys and the 

 other to Paratrachichthys. We were unable to deter- 

 mine whether or not the Aulotrachichthys and Optivus 

 series represented more than one species. Optivus lar- 

 vae were distinguished on the basis of a dorsal count 

 of IV,11, an anal count of 111,9, and the position of the 

 anus, which remains static, immediately anterior to 

 the anal fin. 



Larval development 



Paratrachichthys sp. (Fig. 2) 



Morphology Head length is about equal to body depth 

 at pectoral until flexion, after which body depth in- 

 creases to approximately 50% of body length (Table 2). 

 The mouth is large, reaching to approximately the cen- 

 ter of the eye in our smallest specimen (3.2mm) 

 and beyond the eye in larvae greater than 4.5 mm 

 (Fig. 2A-C). The body depth at anus increases mark- 

 edly during flexion, associated with the anterior mi- 

 gration of the anus during this period. The gas blad- 

 der is inflated and prominent in all specimens. There 

 are 27-29 myomeres. 



Initially the gut is straight and tube like. It quickly 

 thickens, coils, and becomes triangular by approxi- 

 mately 5.0 mm. The anus begins to migrate anteriorly 

 by 6.5mm and is in the adult location (between the 

 pelvics) by 7.8mm (Fig. 2E). The light organ surround- 

 ing the anus first appears in 5.4 mm larvae as an 

 unpigmented, thickened ring. By 6.1mm the light or- 

 gan is lightly pigmented; by 6.9 mm the organ is heavily 

 pigmented and rugose. Notochord flexion commences 

 at about 5.9 mm and is complete by 7.6 mm. 



Fin development Development of the pelvics is pre- 

 cocious. Slight swellings on either side of the gut are 

 present in our smallest specimen 

 (3.2 mm). Distinct buds are present by 

 3.9 mm. The pelvics develop rapidly, hav- 

 ing a full complement of 7 elements by 

 5.6 mm, and reaching up to 347c body 

 length by 7.6 mm. Anlagen of both dorsal 

 and anal fins are present by 4.3 mm. The 

 anlagen first appear as hyaline zones 

 within the fin folds, connected to the body 

 by a series of filamentous extensions in- 

 serted at each myoseptum (Fig. 2B). 

 Bases of the anal and dorsal fins are 

 present by 4.7 mm, and posterior incipi- 



