making bairdiella eggs and larvae extremely 

 favorable material for experimentation. In addi- 

 tion to providing a year-round supply of eggs, 

 laboratory spawning techniques have permitted 

 maintaining bairdiella at different salinities dur- 

 ing maturation and spawning in order to test the 

 effect of parental salinity acclimation on the salin- 

 ity tolerance of the gametes, embryos, and larvae. 



MATERIAL AND METHODS 

 Capture and Maintenance of Fish 



Methods used for collecting and maintaining 

 bairdiella were nearly identical to those described 

 by Haydock (1971). Adult bairdiella were cap- 

 tured with a 60-m beach seine on the west coast of 

 the Salton Sea, just north of the Salton Bay Yacht 

 Club. Rectangular fiberglass tanks of 2,000-liter 

 capacity were used to hold fish in the laboratory 

 and were supplied with continuously flowing 

 warm (22°C) seawater from the Southwest 

 Fisheries Center system (Lasker and Vlymen 

 1969). Water was filtered through pol5T)ropylene 

 GAF'* snap-ring filter bags of 50- ^^m pore size 

 (GAF Corp., Greenwich, Conn.). Mercury lamps 

 provided illumination (Haydock 1971) and the 

 photoperiod was controlled as desired by timers. 



The fish were fed ad libitum twice each day with 

 ground squid, supplemented by ground red crab, 

 Pleuroncodes planipes , at a ratio of approximately 

 1 part of crab to 6 of squid (wet weight). The red 

 crabs were intended as a source of carotenoids 

 because some authors have indicated that paren- 

 tal carotenoid deficiency may affect the viability of 

 offspring (Hubbs and Stavenhagen 1958). 



Several outbreaks of the parasitic ciliate, Cryp- 

 tocaryon irritans Brown, occurred (Wilkie and 

 Gordin 1969) and were effectively controlled by 

 adding copper sulfate at 0.2 ppm as Cu^ ^ in the 

 morning and late afternoon, allowing the chemi- 

 cal to be diluted in the interim by the continuously 

 flowing seawater. Whenever fish were handled, 

 they were subsequently treated with Furacin an- 

 tibiotic (Eaton Veterinary Laboratories, Norwich, 

 N.Y.) at 130 ppm, which was gradually diluted in 

 the open seawater system. This precaution effec- 

 tively controlled bacterial infections and allowed 

 repeated handling of fish without adverse conse- 

 quences. 



FISHERY BULLETIN: VOL. 73, NO. 1 



Induced Maturation and Spawning 



Fish which had ripe gonads when captured were 

 maintained in this condition for several months by 

 exposing them to a photoperiod of 16 h light, 8 h 

 darkness (16L:8D) at approximately 22°C 

 (Haydock 1971). Prolonged exposure of female fish 

 to long days resulted in eventual resorption of the 

 ova. After a group offish had been spawned out or 

 had begun gonadal resorption, they were shifted 

 to a short photoperiod (9L:15D) and colder water 

 (15°C). After being held on short days for a few 

 months, fish could then be brought to maturity by 

 increasing the photoperiod at a rate of 30 min per 

 day until 16L:8D was reached; after about 3 mo on 

 16L:8D at 22°C, the fish had developed mature 

 ovaries and were ready to spawn. Successful 

 spawning could be induced over a period of at least 

 two or three more months before gonadal resorp- 

 tion began. Photoperiod manipulation was effec- 

 tive in inducing ovarian maturation regardless of 

 the time of year, and the experiments described in 

 this paper were conducted in the summer, fall, and 

 winter instead of during the normal spring spawn- 

 ing period. 



Bairdiella kept in the laboratory vary consider- 

 ably in their ovarian development (Haydock 

 1971). In the present study the maturity of female 

 fish was assessed from ovarian biopsies taken with 

 a glass capillary tube (Stevens 1966). At first only 

 the maximum oocyte diameters were recorded 

 immediately after sampling, along with qualita- 

 tive notes concerning the amount of ovarian 

 stroma in the sample. When it became apparent 

 that this was not a sufficiently sensitive measure 

 of the state of maturity, the samples were pre- 

 served in 3% Formalin (in 50% seawater) and all 

 oocyte diameters of 175 /^m or greater were mea- 

 sured with an ocular micrometer a day or so later,^ 

 giving an oocyte size-frequency distribution based 

 on measurements of approximately 100 oocytes. 

 The fish which had been biopsied in this manner 

 were marked individually on the lower jaw with 

 injections of the dye, National Fast Blue 8GXM ( = 

 Fast Turquoise PT) (Kelley 1967; Haydock 1971). 



Mature female fish weighing 100-150 g were 

 injected in the epaxial musculature near the dor- 

 sal fin with 100 lU of gonadotropin from pregnant 

 mare's serum (PMS; Sigma Chemical Co., St. 

 Louis, Mo.) in a carrier of Ringer's solution, after 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



'No measurable oocjrte shrinkage occurred even after a week 

 of preservation. 



