MATARESE ET AL.: LARVAL DEVELOPMENT OF PACIFIC TOMCOD 



47-55^ SL( myomeres 2 1-26) and the posterior bar 

 is at 69-79^f SL (myomeres 36-43). The anterior 

 bar begins posterior to the anus for similar size G. 

 macrocephalus larvae (Figure 5C) at 40-57% SL 

 (myomeres 16-261 and the posterior bar is at 

 59-8 IT^ SL (myomeres 26-42). Differences also 

 exist in the number of melanophores in the stripe 

 within a bar and associated bar length. This latter 

 character, however, is only useful at small sizes 

 (2.5-4.5 mm SL) because melanophores increase 

 with development and the stripes become continu- 

 ous. At 3.6 mm SL (Figure lA), M. proximus lar- 

 vae have on each side two dorsal and four ventral 

 melanophores in the stripes within the small an- 

 terior bar, and seven melanophores each in the 

 longer dorsal and ventral stripes within the pos- 

 terior bar. Similar sized T. chalcogramma larvae 

 (4.1 mm SL) have evenly sized stripes with five 

 melanophores on both the dorsal and ventral 

 stripe of the anterior bar. and five dorsal and seven 

 ventral melanophores in each stripe of the pos- 

 terior bar. Gadus macrocephalus larvae (4.4 mm 

 SL) have longer stripes than the other two species, 

 with 7 dorsal and 8 ventral melanophores on the 

 anterior bar, and 11 dorsal and 10 ventral 

 melanophores on the posterior bar. 



With development these pigment stripes within 

 the bars variously remain separate or become 

 connected depending on the species. In M. prox- 

 imus larvae the ventral stripes become continuous 



at 5.0-6.0 mm SL (Figure IB) while the dorsal 

 stripes remain separate until 13.0 mm SL. The 

 dorsal stripes become continuous in T. chalco- 

 gramma larvae at 13.0 mm SL whereas the ven- 

 tral stripes never connect. Gadus macrocephalus 

 larvae have continuous dorsal and ventral stripes 

 of melanophores by 5.0-6.0 mm SL (Figure 5C). 



Other pigment differences may help in distin- 

 guishing species at certain size ranges. Early G. 

 macrocephalus larvae (4.0-8.0 mm SL) have more 

 head pigmentation than the other two species, 

 particularly on the dorsal surface and in the snout 

 area (Figure 5C). Theragra chalcogramma larvae 

 (<13.0mm SL) have much less lateral pigment on 

 the surface of the gut than either M. proximus or 

 G. macrocephalus larvae (Figure 5B). Gadus mac- 

 rocephalus larvae (5.0-8.0 mm SL) have more 

 mediolateral pigmentation between the postanal 

 bars than the other two species in that size range 

 (Figure 5C). Caudal pigment also differs and at 

 sizes <10.0 mm SL can separate M. proximus. 

 Only M. proximus larvae have a single row of 

 ventral caudal melanophores posterior to the anal 

 fin (Figure ID) whereas both T. chalcogramma 

 and G. macrocephalus larvae have isolated pig- 

 ment spots (Figure 5B, D). 



Also helpful in distinguishing M. proximus lar- 

 vae from the other two species is the possession of 

 five rays on the superior hypural compared with 

 four rays for T. chalcogramma and G. mac- 



TabLE 7. — Characters useful in separating lar\'ae of Microgadus proximus, Theragra chalcogramma, and Gadus macrocephalus at 



specific size ranges. 



Character 



Size range 

 (mm) 



Microgadus 

 proximus 



Theragra 

 chalcogramma 



Gadus 

 macrocephalus 



Anterior pigment bar 

 Percentage of SL 

 Located at myomeres 

 Posterior pigment bar 

 Percentage of SL 

 Located at myomeres 

 Number of melanophores in each stripe of; 

 Anterior bar 

 Dorsal 

 Ventral 

 Posterior bar 

 Dorsal 

 Ventral 

 Degree of stripe continuity; 

 Anterior bar: 

 Dorsal 

 Ventral 

 Posterior bar; 

 Dorsal 

 Ventral 

 Head melanophores 



fvlelanophores on ventral surface of gut 



Lateral pigment on gut surface 

 Mediolateral pigment In postanal region 

 Ventral caudal pigment 

 Number of rays on superior hypural element 



5-6 



937 



