MATARESE ET AL.: LARVAL DEVELOPMENT OF PACIFIC TOMCOD 



Table 4. — Body proportions of larvae and juveniles of Microgadus proximus. Values given for each body proportion are expressed 

 as percentage of standard length (SL) or head length (HL): mean, standard deviation, and range. 



'Sample size is 12 for upper jaw length, 



^Sample size is 1 6 each for distances from snout to first dorsal fin and snout to second dorsal tin; 1 2 for distance from snout to third dorsal fin; 1 5 for distance 

 from snout to first anal fin; and 9 for distance from snout to second anal fin. 



on the dentary exceeds the number on the pre- 

 maxilla, but this is reversed at about 23 mm SL 

 with the difference increasing with growth. A 

 similar change in number and location of teeth 

 was reported to occur on the Pacific whiting, Mer- 

 luccius productus (Ahlstrom and Counts 1955). 



In larval and transforming specimens (11.9-22.3 

 mm SL), teeth are irregularly spaced and clus- 

 tered in groups. Some are caninelike and others 

 are recurved. As the larvae grow, the teeth become 

 more closely spaced as the numbers of teeth in- 

 crease and approach biserialization in 34.3 mm SL 

 juveniles, similar to that described for Pacific 

 whiting (Ahlstrom and Counts 1955). 



Gill rakers begin ossifying at 9.6 mm SL and all 

 (3 + 20 = 23) gill rakers are ossified in a 24.3 mm 

 SL larva. 



Neural spines in the abdominal region begin to 

 ossify at about 8.7 mm SL and all are ossified by 11 

 or 12 mm SL. Ossification generally proceeds pos- 

 teriorly. Neural spines of the caudal region also 

 begin ossifying at about 8.7 mm SL but ossification 

 is not complete until specimens are 17 mm SL. The 

 neural and haemal spines of the third to sixth 

 vertebrae preceding the postural centrum begin to 

 accept alizarin stain before other neural spines in 

 the caudal region. Haemal spines ossify in a se- 

 quence similar to neural abdominal spines; all 

 spines are ossified by 17 mm SL. The last neural 

 and haemal spines to ossify are those associated 

 with the terminal preural vertebrae. These spines 

 are broadly flattened and ossify simultaneously 

 with other bones of the caudal complex, as dis- 

 cussed later (Figure 3). 



Vertebral centra in both the abdominal and 

 caudal regions begin to ossify at about 8.7 mm SL 

 and ossification is completed by 11 mm SL and 



about 19 mm SL. Ossification proceeds from an- 

 terior to posterior. 



Fins 



Median and paired fins showed some variation 

 in development, with fin rays first forming at dif- 

 ferent body lengths in individual specimens (Table 

 5). Fin formation occurs in the sequence: larval 

 pectoral fins; caudal fin; first anal fin; second anal 

 fin; third, second, and first dorsal fins (nearly 

 simultaneously); pelvic fins; and pectoral fins with 

 rays. 



The pterygiophores supporting anal and dorsal 

 fin rays begin ossifying at 23.4 mm SL and os- 

 sification is complete by 31.1 mm SL. Too few 

 specimens were available to follow the sequence of 

 ossification. 



Larval pectoral fins are present in our smallest 

 specimen (2.7 mm SL). They consist of a fleshy 

 base and an undifferentiated membrane. They 

 persist until rays begin differentiating late in the 

 larval period. 



The caudal fin of M. proximus is associated with 

 a complex of 16 centra (2 ural and 14 preural 

 centra), 14 neural and haemal spines. 2 epurals, 1 

 superior hypural (HY 4-6), and 2 inferior hypurals 

 (HY2-3,HY1) (Figure 3). 



Caudal rays total 49-56, of which 22-25 are dor- 

 sal in origin, 22-26 are ventral in origin, and five 

 are normally supported by the superior hypural. 

 Principal caudal rays number 32-33; of these, 12 or 

 13 are dorsal in origin and 13 or 14 are ventral in 

 origin. One each is attached to the two epurals, five 

 are carried on the superior hypural, two on 

 hypural 2-3, and one on hypural 1. 



As with the Pacific whiting (Ahlstrom 



931 



