MATARESE ET AL.: LARVAL DEVELOPMENT OF PACIFIC TOMCOD 



Table 6. — Numbers of teeth on premaxillary and dentary bones 

 in selected sizes of larval and juvenile Microgadus proximus. 



complete in the first anal fin at 23.0 mm SL and in 

 the second anal fin at 27 or 28 mm SL. Ray develop- 

 ment within a fin proceeds anterior to posterior. 



Dorsal fins develop in a manner analogous to the 

 anal fins and the three dorsal fins develop almost 

 simultaneously. Dorsal fins 2 and 3 commence os- 

 sification at 12.9 mm SL, and dorsal fin 1 begins 

 accepting stain at 13.2 mm SL. Ossification is 

 complete in the first and second dorsal fins at 22.0 

 mm SL and in the third dorsal at 28.0 mm SL. Rays 

 ossify from anterior to posterior. 



Pelvic buds appear at about 8.0 mm SL. Pelvic 

 fins begin ossifying at about 14.0 mm SL and are 

 consistently ossified in 26.0 mm SL early juve- 

 niles. Pectoral fins initiate ossification at 15.0 mm 

 SL and reach their full complement of 18-20 rays 

 in 28.0 mm SL juveniles. 



Scales 



Scales begin developing in the anterior portion 

 of the body near the dorsal tip of the cleithrum in 

 28.6 mm SL specimens. Development appears to 

 progress along the lateral line as the juveniles 

 grow. Scale development was not complete in our 

 largest specimen, 41.1 mm SL. 



Occurrence of Microgadus proximus 

 (Figure 4) 



Although a number of ichthyoplankton studies 

 have been conducted in the northeastern Pacific 

 Ocean, data on occurrence of M. proximus are 

 limited because of past difficulties in distinguish- 

 ing the larvae from other gadids. Larvae of this 

 species may be included under the broader cat- 

 egory of Gadidae listed in some papers (e.g., 



Waldron 1972; Pearcy and Meyers 1974). Some 

 data on distribution and seasonal abundance, 

 however, are available. 



Larvae of M. proximus are found in coastal 

 waters off Oregon occurring mainly within 18 km 

 of shore with abundance peaks at about 6 and 9 km 

 (Richardson and Pearcy 1977; Richardson^). A few 

 specimens have been reported as far as 74 km 

 offshore (Richardson footnote 8). 



The larvae have been collected in the plankton 

 off Oregon from February through August with 

 peak abundance from March through July 

 (Richardson footnote 8). Misitano ( 1977) also col- 

 lected four specimens, 5-61 mm SL, from March to 

 July in the Columbia River mouth. 



Monthly length frequencies and median lengths 

 of larvae collected in 1971 and 1972 off Oregon 

 indicate a winter-spring spawning period (Figure 

 4). Small larvae, ^5 mm SL, were collected Feb- 

 ruary through June. 



Larvae of M. proximus were collected 24 km off 

 coastal Washington (Cruise K-72-2-III) in early 

 June 1972, by the NWAFC^. This species ac- 

 counted for 22.2% of the total catch offish larvae, 

 and specimens ranged from 5.0 to 26.0 mm SL. 



COMPARATIVE NOTES ON 



THERAGRA CHALCOGRAMMA AND 



GADUS MACROCEPHALUS 



(Figure 5, Table 7) 



In the northeastern Pacific Ocean, larvae of M. 

 proximus are similar to those of T. chalcogramma 

 and G. macrocephalus at sizes <16.0 mm SL. Iden- 

 tification of all three species in mixed samples is 

 difficult with previously available literature, 

 which describes T. chalcogramma and G. mac- 

 rocephalus from the northwestern Pacific Ocean 

 (e.g., Gorbunova 1954; Uchida et al. 1958; 

 Mukhacheva and Zviagina 1960). We have sum- 

 marized characters which are useful to distin- 

 guish each species at sizes <16.0 mm SL based on 

 our examination of specimens of all three species 

 (Table 7). 



The most useful character to separate the 

 smaller larvae (hatching to 10.0 mm SL) of the 



»Richardson, S. L. 1977. Larval fishes in ocean waters off 

 Yaquina Bay, Oregon: abundance, distribution, and seasonality 

 Januarv 1971 to August 1972. Oregon State Univ., Sea Grant 

 Coll. Program Publ. ORES-T-77-003, 73 p. 



^Data on file for Cruise K-72-2 (III), 1972, Northwest and 

 Alaska Fisheries Center, National Marine Fisheries Service, 

 NOAA, 2725 Montlake Blvd. E., Seattle, WA 98112. 



935 



