FISHERY BULLETIN: VOL. 80. NO. 1 



age at length for larvae of this species and 

 describes the growth of larvae collected in 

 Oregon coastal waters during the 1977-78 

 spawning season. It is the first detailed study of 

 larval growth of a pleuronectid throughout the 

 pelagic period, and further, provides a basis for 

 the documentation of growth during trans- 

 formation to the adult form (Rosenberg and 

 Laroche 1982) and of juveniles in nursery 

 grounds off the Oregon coast (Rosenberg 1980). 



METHODS 



Spawning and Rearing Procedures 



Ripe adult P. vetulus were collected during fall 

 and winter 1978 with a 12 m otter trawl off the 

 Oregon coast in the vicinity of Hecata Head, 

 approximately lat. 44°10'N, long. 124°18'W, 

 68-77 m water depth. Eggs were artificially fer- 

 tilized on shipboard (Bagenal and Braum 1971) 

 and transported back to the laboratory in sea- 

 water-filled plastic bags. 



In the laboratory, eggs were incubated and 

 larvae reared at 12°-13°C and under a 14-h light, 

 10-h dark photoperiod in filtered seawater taken 

 from the area where the adults were captured. 

 Eggs held in 4 1 glass jars hatched in 3-3% d. The 

 newly hatched larvae were transferred by 

 pipette to new 4 1 glass jars or 8 and 9 1 plastic 

 tubs in which a bloom of the green flagellate 

 Tetraselmis sp. was maintained throughout the 

 rearing period. Approximately every 2 d, one- 

 fourth to one-third of the water in rearing con- 

 tainers was replaced. On day 4 after hatching, 

 Gymnodinium splendens, a naked dinoflagellate, 

 and Brachionus plicatilis, a rotifer, were intro- 

 duced into the rearing containers. After 1-2 wk, 

 G. splendens was no longer added because larvae 

 did not appear to eat this organism. Prey con- 

 centrations were not measured but B. plicatilis, 

 the primary food item, was maintained at high 

 levels, i.e., rotifers were readily visible through- 

 out rearing containers. Artemia salina nauplii 

 and the harpacticoid copepod, Tisbe sp., pro- 

 vided secondary food sources. 



One to ten larvae were preserved in ~80% 

 ethanol each day after hatching for the first 35 d; 

 subsequently, older larvae were preserved at 

 irregular intervals. Larvae were reared from 

 two separate spawnings, in early and late fall 

 1978, but since rearing conditions were identi- 

 cal, age and growth data from the two were com- 

 bined. 



Field and Laboratory Procedures 



Parophrys vetulus larvae were collected in the 

 field with 70 cm, 0.505 mm mesh bongo nets in 

 bottom to surface stepped, oblique tows. Samples 

 were taken approximately monthly from 

 November 1977 to June 1978 in Yaquina Bay, 

 Oreg., and 2-7 km offshore (lat. ~44°37'N; long. 

 124°05'W). Samples were drained and pre- 

 served in ~80% ethanol; within 12-18 h the 

 samples were drained again and fresh preserva- 

 tive was added. With each plankton sample sur- 

 face temperature, surface and bottom salinity 

 were recorded and a bathythermograph cast was 

 made. 



In the laboratory all fish larvae were removed 

 from plankton samples and stored in ~80% 

 ethanol. Otoliths were removed from P. vetulus 

 larvae within 6 mo of initial preservation be- 

 cause longer storage resulted in erosion or com- 

 plete dissolution of the otoliths. 



Prior to otolith removal P. vetulus larvae were 

 placed in freshwater for ~l-2 min (somewhat 

 longer for specimens >15 mm) to remove or di- 

 lute ethanol in the tissue. A larva was then placed 

 in a drop of water on either a glass slide or large 

 rectangular cover slip under a dissecting micro- 

 scope fitted with polarizing filter and analyzer. 

 Standard length (SL) was measured with an 

 ocular micrometer to the nearest 0.1 mm and 

 both sagittae were dissected out with fine probes 

 at 25 X or 50 X magnification. The larva was re- 

 moved from the slide or slip and the otoliths were 

 left to dry concave side up. Sagittae were then 

 permanently mounted under a cover slip with 

 Pro-Texx, 3 a clear mounting medium. Rectan- 

 gular cover slip mounts, which were thought to 

 improve the optical properties of the preparation, 

 were taped for support to a thin piece of brass for 

 viewing under the microscope. 



Otolith growth increments, consisting of an 

 inner light band and a narrower, sharply 

 delineated, continuous outer dark band adjacent 

 to it, were counted using a compound micro- 

 scope with bright field illumination at 800 X or 

 1,250 X magnification. Faint bands inside the 

 otolith nucleus in reared larvae and "subdaily" or 

 weak rings between well-defined growth incre- 

 ments in some older (>30 d old) field-caught fish 

 were not counted. Counts were made on only one 

 sagitta of the pair and were repeated until a 



:i Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



94 



