FISHERY BULLETIN: VOL. 69. NO. 2 



slowly in intensity as the sun rose and no abrupt 

 dark-light transition was imposed upon the 

 larvae. 



CONTAINERS 



The containers used for rearing larvae in this 

 study were the same as those described by Las- 

 ker et al, 1970) , being circular (35 cm diameter, 

 14 cm deep) and made of the plastic alloy Ky- 

 dex.' These containers have nonglossy black 

 surfaces and hold 10 liters of seawater. For 

 feeding studies with individual larvae, smaller 

 Kydex containers were used (10.5 cm diameter, 

 4.2 cm deep) which held 300 ml of water. Both 

 large and small containers were covered with 

 clear plexiglass tops to reduce evaporation and 

 keep out dust particles. 



FEEDING 



Nauplii of the brine shrimp, Artemia salina, 

 were used exclusively as a food source. Artemia 

 nauplii have proven to be poor food for larval 

 clupeids but excellent for several other types 

 of larvae (May, in press), and they appear to 

 satisfy the nutritional requirements of larval 

 grunion. Nauplii were obtained by hatching 

 San Francisco brine shrimp eggs in trays mo- 

 deled after those described by Riley (1966). 

 Two trays were used, which allowed harvesting 

 of trays on alternate days with a time lapse of 

 48 hr between inoculation of eggs and harvesting 

 of nauplii. The water in the trays was kept 

 at about 20° C. Nauplii were rinsed in filtered 

 seawater and added to rearing containers shortly 

 after the lights went on each morning, and more 

 were added during the day if the concentration 

 dropped low enough to prevent ad libitum feed- 

 ing. If any uneaten nauplii remained from the 

 previous day, as many as possible were removed 

 by pipette before the morning addition of new 

 nauplii. Fecal matter was siphoned daily from 

 the bottoms of the "fed" containers. 



' Kyde.x is manufactured by Rohm and Haas, Phil- 

 adelphia, Penn. Use of trade name does not imply 

 endorsement of the product. 



QUANTITATIVE FEEDING STUDIES 



At 3-day intervals beginning on day 1, 6-day 

 quantitative feeding experiments were begun to 

 measure the food consumption and growth of 

 previously fed and unfed larvae. Larvae were 

 transferred individually, from both the "fed" 

 and the "unfed" suppl.v containers, to small (300 

 ml) containers late in the afternoon on the day 

 before the beginning of the feeding experiment. 

 Three larvae from a "fed" container and three 

 from an "unfed" container were used in each 

 feeding experiment; individual larvae were kept 

 in separate containers during the feeding study. 



On the morning following transfer to the feed- 

 ing containers, and for six mornings thereafter, 

 a known number of Artemia nauplii was counted 

 out with a pipette under a dissecting microscope 

 and added to each container. Shortly before 

 the lights went off at the end of the day, the 

 grunion larvae were transferred by pipette to 

 new containers, and the uneaten Artemia in the 

 old containers were concentrated on a nylon 

 mesh, preserved in Formalin and later counted. 

 The difference between the number of nauplii 

 added in the morning and the number left at 

 the end of the day gave the number eaten by a 

 larva. At the start of the series of feeding ex- 

 periments, on day 1, 100 nauplii were added to 

 each experimental container; when larvae con- 

 sumed 70% or more of the nauplii offered, the 

 number offered the following day was increased 

 bv 50 nauplii. On the morning following the 

 final (6th) day of feeding, the experimental 

 larvae were collected and analyzed as described 

 below. The weight of a larva at the start of 

 the feeding experiment, estimated from the 

 mean weight of 10 larvae sampled at that time, 

 was subtracted from the weight of the exper- 

 imental larva at the end of the feeding period 

 to yield its gain in dry weight. 



In order to determine the weight of the in- 

 gested material, the weight of a single Artemia 

 nauplius was estimated by making several 

 weighings on an electrobalance' of groups of 5 

 to 20 nauplii, collected at the same interval after 

 inoculation of eggs as the nauplii used in the 

 feeding study. The nauplii were rinsed with 

 distilled water and dried to constant weight at 



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