EFFECTS OF SEEDING DENSITY OF PINK SALMON, 

 ONCORHYNCHUS GORBUSCHA, EGGS ON WATER CHEMISTRY, FRY 

 CHARACTERISTICS, AND FRY SURVIVAL IN GRAVEL INCUBATORS 



Jack E. Bailey, Stanley D. Rice, Jerome J. Pella, and Sidney G. Taylor' 



ABSTRACT 



We determined the effects of seeding density of pink salmon eggs in gravel incubators on water 

 chemistry and on size, stage of development, and time of emergence of fry. Sixty days after fertilization, 

 eyed eggs were placed in eight identical test incubators at five different densities ( to 25,600 eggs per 

 incubator). Test incubators had upwelling water ( apparent velocity, 53 cm per hour); 0.015 m^ of gravel 

 (size, 3-32 mm); and an average incubation temperature of 4.5° C (range, 3.5°-10.0° C). Total ammonia 

 (NH3 + NH4*) production and oxygen consumption rates per alevin generally increased throughout 

 incubation. Maximum total ammonia production at any density was about 8 x lO"* mg/h per alevin. 

 Maximum oxygen consumption was 0.028 mg/h per alevin. The rate of ammonia production and 

 oxygen consumption per alevin increased with increased seeding density until the reduced oxygen 

 concentration limited metabolism. Indications of stress — reduction in size of fry and early 

 emergence— were evident only at the higher seeding densities, 12,800 and 25,600 eggs per 0.015 m^, 

 and were either absent or unimportant at the lower seeding densities, 1,600 and 6,400 eggs per 0.015 

 m^. Un-ionized ammonia ( NH3 ) concentrations did not reach lethal levels. The stress at higher seeding 

 densities, 12,800 and 25,600 eggs per 0.015 m^, was probably caused by depletion of oxygen to 

 concentrations below 6 mg/1. Sublethal ammonia concentrations and low dissolved oxygen concentra- 

 tions were probably synergistic. 



Gravel incubators with upwelling water are being 

 tested at hatcheries in the Pacific Northwest for 

 production of fry from eggs of pink salmon, On- 

 corhynchus gorbuscha, chum salmon, O. keta, and 

 sockeye salmon, O. nerka. To operate most 

 economically, these incubators must be stocked 

 with optimum numbers of eggs and be supplied 

 with a flow of water consistent with production of 

 good quality fry. Frugal use of water is important 

 to hatcheries in Alaska where long, cold winters 

 limit free-flowing water. However, densities of 

 eggs that are too high for water flows result in 

 oxygen depletion or ammonia buildup — stressing 

 conditions that produce undersized fry or early 

 emerging alevins. Both undersized fry and early 

 emerging alevins are believed to survive poorly if 

 released unfed (Bams and Simpson 1977). 



Acute ammonia toxicity may not be a significant 

 problem in Alaska where waters typically have 

 low temperature and low pH. Ammonia equili- 

 brates in water to form dissolved, un-ionized NH3 



and ionized NH. 



(NH3 is more toxic than NH4 



), 



and low temperature and low pH shift the equilib- 



'Northwest and Alaska Fisheries Center Auke Bay Labora- 

 tory, National Marine Fisheries Sevice, NOAA, PO. Box 155, 

 Auke Bay AK 99821. 



Manuscript accepted January 1980. 

 FISHERY BULLETIN: VOL. 78, NO. 3, 1980. 



rium toward NH^^ (Emerson et al. 1975). At lower 

 temperatures, however, salmon incubation times 

 are longer than at higher temperatures so that 

 increased cumulative exposure to NH3 could have 

 adverse effects. 



In this paper we describe effects of seeding den- 

 sities of pink salmon eggs in gravel incubators on 

 1 ) oxygen consumption, 2 ) ammonia production, 3 ) 

 physical characteristics of fry, 4) survival of fry, 

 and 5) time of volitional emergence. The produc- 

 tion limits of the gravel incubators are also de- 

 fined. 



METHODS 



Experimental gravel incubators were seeded 

 with different densities of eggs. Temperature, pH, 

 dissolved oxygen, and total ammonia (NH3 and 

 NH4 + ) concentrations were measured in water en- 

 tering and leaving the incubators. Rates of oxygen 

 consumption and ammonia production per egg or 

 alevin were estimated during incubation. We mon- 

 itored numbers and size of fry and time of 

 emergence of fry to identify stressful conditions. 

 Chemical data were compared with biological data 

 to determine maximum seeding densities for the 

 gravel incubators and to define limits of oxygen 



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