Trnski et al.: Larval development of Macquana colonorum and M. novemaculeata 



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form as larvae develop; four or five spines are present 

 in larvae and transitional juveniles from 7.5-8.2 mm. 

 A minute spine (rarely two) develops on the anterior 

 preopercular border from 9 mm; a third spine devel- 

 ops in transitional juveniles from 13.3 mm. A small 

 interopercular spine develops by the time notochord 

 flexion is complete. Low posttemporal and supraocular 

 ridges, but no spines, develop during notochord flexion; 

 they both become inconspicuous in postflexion larvae 

 from 8.2 and 8.6 mm, respectively. An opercular spine 

 is present from 8.6 mm. A small supracleithral spine is 

 present in transitional juveniles from 10.1 mm. 



The pterygiophores of all the soft rays and up to six 

 of the pterygiophores of the first dorsal fin form during 

 notochord flexion. Soft rays of the dorsal fin are ossi- 

 fied by the time notochord flexion is complete, whereas 

 spinous rays ossify from posterior to anterior in late 

 flexion and early postflexion larvae by 5.7-6.1 mm. The 

 full complement of spines is present by 8.2 mm. Anal- 

 fin pterygiophores form during notochord flexion, and 

 all soft rays are ossified by the time notochord flexion 

 is complete. Spinous rays of the anal fin begin to ossify 

 in postflexion larvae by 6.3 mm, and all anal-fin ele- 

 ments are present by 7.2 mm. The last spinous ray of 

 the dorsal fin and the third spinous ray of the anal fin 

 transform from a soft ray between 7.6 and 9.2 mm. Pec- 

 toral-fin elements begin to ossify by the time notochord 

 flexion is complete, and all rays are present in postflex- 

 ion larvae by 7.5 mm. Pelvic-fin buds form in postflexion 

 larvae by 6.7 mm, and all elements are ossified by 8.2 

 mm. Caudal-fin rays first appear in preflexion larvae 

 from 4.6 mm, and all principal rays are ossified by the 

 time notochord flexion is complete. Procurrent caudal 

 rays are present in field-caught transitional juveniles. 

 Notochord flexion commences between 4.6 and 5.0 mm, 

 and is complete by 5.6-6.1 mm. There is a prominent 

 gap between the anus and anal fin while the anal fin 

 forms (vent to anal-fin length [VAFL] up to 5% of BL). 

 The gap reduces in size as the anal fin develops, and it 

 is absent by 7.6 mm. Scales have not developed in the 

 largest specimen examined. 



Pigment (Fig. 2, A-F) Larvae are moderately to heav- 

 ily pigmented. An expanded melanophore is present on 

 the tip of the snout and a small melanophore develops 

 under the tip of the lower jaw in preflexion larvae from 

 3.6 mm. A second melanophore on the snout develops 

 posterior to the first by the time notochord flexion is 

 complete. A single melanophore is present at the angle 

 of the lower jaw. A few small melanophores develop 

 ventrally along the lower jaw in postflexion larvae from 

 7.2 mm. A series of internal melanophores underlie the 

 mid- and hindbrain. 



There are two very large expanded melanophores 

 on the dorsal midline of the tail; the first is on the 

 trunk centered over the hindgut, and the second is 

 mid way along the tail. Once the dorsal fin forms they 

 are centred under the middle of the spinous portion of 

 the dorsal fin and under the posterior end of the soft 

 dorsal fin, respectively. An additional smaller expanded 



melanophore is present from 7.2 to 7.5 mm on the dorsal 

 midline of the nape above the pectoral-fin base. 



Two very large expanded melanophores occur ven- 

 trally, opposite the two large dorsal melanophores. The 

 anteriormost of these melanophores reduces in promi- 

 nence as larvae develop and is inconspicuous to absent 

 by metamorphosis. Internal expanded melanophores 

 over the gas bladder may have filaments that emerge 

 externally, particularly in preflexion and flexion lar- 

 vae. Internal melanophores along the notochord may 

 be apparent on the caudal peduncle in postflexion lar- 

 vae from 7 mm. There is an expanded melanophore on 

 the midline of the isthmus, immediately anterior to 

 the cleithral symphysis. A series of three to six small, 

 expanded melanophores is present along the ventral 

 midline of the gut. In postflexion larvae there is a bi- 

 laterally paired melanophore anterior to the pelvic-fin 

 base, and two to four melanophores along the midline 

 of the gut between the pelvic-fin base and the anus. A 

 small contracted melanophore ventrally on the posterior 

 margin of the caudal-fin base develops between 5.0 and 

 6.1 mm, and is located between ventral rays 1-5. This 

 melanophore expands from 6.7 to 7.6 mm and spreads 

 across up to four ray bases. 



Pigment distribution spreads rapidly over most of the 

 head from 7.2 to 7.5 mm, and laterally on the trunk, 

 gut and tail from 8.2 mm. The expanded melanophores 

 on the dorsal and ventral midlines of the trunk and 

 tail remain large as the larvae develop; the posterior- 

 most of these increases in intensity in reared larvae. 

 The expanded melanophores on the dorsal and ventral 

 midlines of the body become relatively smaller after 

 settlement. By settlement, small melanophores develop 

 on the membranes of the pectoral, pelvic, anal, and cau- 

 dal fins, and the membrane of the spinous portion of the 

 dorsal fin becomes heavily pigmented. After settlement, 

 small melanophores cover most of the head and body, 

 but the heaviest cover is seen dorsally. Three broad 

 vertical bands become apparent dorsally on the nape, 

 below the center of the spinous dorsal fin, and below 

 the center of the soft dorsal fin in the largest specimen 

 examined (14.1 mm). 



Discussion 



Adults of M. colonorum and M. novemaculeata, which 

 have only minor morphological differences, such as the 

 relative length of the snout, the profile of the head dor- 

 sally, postorbital head length, and gill-raker counts, are 

 difficult to distinguish (Williams, 1970). None of these 

 characters are useful for distinguishing larvae. The 

 larvae of these two species could be positively identified 

 only by comparison with reared larvae derived from 

 positively identified brood stock. 



Melanophore distribution is the most distinguishing 

 character between the larvae of M. colonorum and M. 

 novemaculeata. Macquaria colonorum has between four 

 and seven expanded melanophores along the dorsal 

 midline of the trunk and tail between 4.8 and 7.1 mm. 



