644 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



measuring. If the 25- to 30-mm. late meta- 

 morphic larvae taken May 20 represent the same 

 population as the 80 to 120 mm. juveniles taken on 

 June 19 (table 14), a growth of more than 2 mm. 

 per day is indicated, a rate of increase almost 

 double the highest rate in my experiments, + 1.286 

 mm. for specimen No. 1 for growth between 60 and 

 96 mm. 



Alikunhi and Rao (1951) reported a maximum 

 increase "following metamorphosis" of 29 mm. 

 (35 mm. to 64 mm.) in 160 days for specimens in 

 cement nurseries, or a rate of +0.181 mm. per day. 

 The maximum increase they reported for growth 

 in a laboratory aquarium during the same period 

 was 100 mm. (35 mm. to 135 mm.), or a rate of 

 + 0.625 mm. per day. This rate is comparable to 

 my average for growth during the late meta- 

 morphic and juvenile periods (+0.663 mm. per 

 day, including all specimens) . 



The periods of little or no length increase for 

 late metamorphic larvae and older fish in my ex- 

 periments (fig. 31) are not explained, but might 

 be attributed to type and quantity of food offered 

 (the rate rose sharply during August when two 

 feedings a day commenced). The rate for speci- 

 men No. 1 rose sharply after June 20 when it be- 

 gan to eat pieces of fish (late metamorphic 

 period ) . 



Tolerance to abrupt changes in salinity. — Ex- 

 periments to determine the tolerance of late meta- 

 morphic larvae 25-30 mm. long to sudden changes 

 in salinity were inconclusive. Fish captured from 

 marsh water were placed in beach water to which 

 varying amounts of distilled water had been 

 added. The salinity of the marsh water was 14.8 

 parts per thousand, and that of the beach and 

 combination of beach and distilled water ranged 

 from 17.0 to 26.8 ppt. On the day of capture, the 

 fish placed in water with a salinity exceeding 

 22,0 ppt, died within an hour, but on the follow- 

 ing day other specimens tolerated a higher salin- 

 ity. The shock the fish experinced during han- 

 dling the day they were captured probably 

 affected their response to the difference in salinity 

 or other water conditions. Alikunhi and Rao 

 (1951) reported complete success in transferring 

 "leptocephali" from water with a salinity of about 

 18 ppt, to completely fresh water, by stages and 

 by direct transfer. I transferred no larvae from 

 saline to nonsaline water. 



OCCURRENCE OF LARVAE 



Figure 1 shows the locations of capture for 

 leptocephali from waters off the south Atlantic 

 coast of the United States in 1953. Except for 

 the 28.0-mm. specimen taken May 5 off Charleston, 

 S.C., all were taken during October and Novem- 

 ber. The largest leptocephalus, 31.3 mm., was 

 taken nearest the coast, several miles off between 

 Cape Lookout and Cape Hatteras, N.C., on No- 

 vember 12. I believe it was captured during its 

 migration to the beach, and that it occupied an 

 offshore habitat during its early development. 

 The other leptocephali were from waters of 100 

 fathoms or deeper, except for several taken at a 

 single location on the 20- fathom curve. 



Table 14 and figure 32 show the seasonal 

 occurrence of early metamorphic larvae (shrink- 

 ing) by size groups in biweekly seine samples 

 from beach and marsh habitats near Brunswick, 

 Ga., between March 1953 and October 1956. The 

 earliest occurrence was March 15, the latest, 

 October 23, but most (by number and frequency 

 of occurrence) were taken during April and early 

 May. In April 1953 they appeared first on the 

 beach, then in the marsh, and in May they occurred 

 only in the marsh. In 1954, 1955, and 1956 only 

 one metamorphic larva was taken in the marsh. 

 All late metamorphic larvae were taken in the 

 marsh. The greater numbers of early, mid-, and 

 late metamorphic larvae taken during 1956 prob- 

 ably reflect the increased efficiency of the larger 

 seine used during that year. 



How much time elapses between hatching of the 

 egg and appearance of early metamorphic larvae 

 on the beach is unknown. If the early meta- 

 morphic larvae that appear on the beaches of 

 Georgia during March, April, and May (fig. 32) 

 are of the same population as the leptocephali 

 taken offshore in October and November, it would 

 indicate slow growth during the winter months of 

 November through February, and an age of about. 

 6-8 months when they reach the beaches. I be- 

 lieve the smallest leptocephali taken offshore, 5.1 

 and 5.3 mm., are recently hatched fish, possibly 

 only a few days old. Larger leptocephali (10- 

 20 mm.) taken during October possibly were 

 spawned within a month of capture. The extent 

 of the spawning season is not indicated, only that 

 there is spawning during the fall. However, the 



