EFFECT OF LONG-TERM AMMONIA 



EXPOSURES ON SIZE OF 



FRY AT EMERGENCE 



Lengthy exposure of alevins to NH, resulted in 

 fry that were smaller than control fry at 

 emergence (Figure 2). Although the three test 

 groups of alevins (groups A, B, and C) were ex- 

 posed to NH3 for different time periods (21, 40, and 

 61 d), they were all sampled when the control 

 groups had completed yolk absorption. The high- 

 est exposure concentration of NH3 (4 ppb) caused 

 significant decreases in weight (P<0.05) of ex- 

 posed fry in all three exposure groups. At exposure 

 concentrations <4 ppb, the groups held for 40 d 

 and 61 d (B and C) were similar in response: both 

 were significantly smaller in length and weight 

 after exposure to 2.4 ppb NH3; after exposure to 1.2 

 ppb there was no significant difference. Effects 

 were consistently more adverse for group C, the 

 group receiving the longest exposures. The statis- 

 tically significant decrease in weight (P<0.05) of 

 one observation of group A exposed to 0.2 ppb of 

 NHg appeared to be an aberrant observation. 



EFFECT OF AMMONIA ON 

 EARLY EMERGENCE 



Short-term (24 h) exposures to low concentra- 

 tions of NHg (<25 ppb) did not stimulate early 

 emergence during or immediately after the expo- 

 sures; emergence patterns were the same as those 

 of unexposed fry. At higher concentrations (30-50 

 ppb) of NHg, early emergence of the alevins (up to 

 11%) occurred within 24 h of exposures, but little 

 residual effect was observed later when 50% 

 emerged at approximately the same date as unex- 

 posed alevins (Figure 3). Some early emergence of 

 the alevins (up to 12%) occurred at high concen- 

 trations of 100-150 ppb NH3, but massive early 

 emergence was not observed even though these 

 concentrations were above the 96-h TLm's for ale- 

 vins or fry during the period 15 February to 10 

 April (Figure 1). Although the high concentra- 

 tions were probably stressful, mortalities never 

 exceeded 4%. In all cases, when early emergence 

 was stimulated, it occurred within 24 h of the 

 beginning of exposure. In response to the acute 

 exposures to NH3, the alevins that emerged early 

 had visible amounts of yolk, indicating they were 

 not ready for normal emergence. The alevins that 

 did not emerge during or immediately after NH3 

 exposures stayed in the incubators almost as long 



644 



FISHERY BULLETIN: VOL. 78, NO. 3 



as the unexposed alevins and emerged without 

 any visible yolk. 



IMPLICATIONS OF 

 AMMONIA EXPOSURE STUDIES 



Ammonia exposures resulting in immature or 

 small fry would be detrimental to the survival of 

 pink salmon fry because these small fish are easily 

 preyed upon (Bams 1967; Parker 1971). We did 

 observe some early emergence of immature fry 

 during or immediately after short-term exposures 

 to NHg, but only at the high concentrations that 

 aproached highly toxic levels. These high concen- 

 trations are not likely to be encountered in natural 

 or hatchery environments, but if they were en- 

 countered, the immature alevins that emerged 

 with visible yolk would have difficulty swimming 

 and avoiding predators. 



We do not know the effect of long-term expo- 

 sures to low concentration of NHg on time of volun- 

 tary emergence, but these tests do produce emer- 

 gent fry with decreased weight and length. 

 Exposed emergent fry have increased metabolic 

 rate and, therefore, increased demand on yolk re- 

 serves and less yolk reserve available for incorpo- 

 ration into developing tissues. Adult trout exposed 

 to NH3 have increased metabolic rates, and NHg 

 probably has the same toxic action in fishes that it 

 has in mammals — impairment of cerebral energy 

 metabolism (Smart 1978). 



The lowest concentration of NH3 that caused fry 

 to be significantly smaller in length and weight at 

 emergence was 2.4 ppb (61- and 40-d exposures) 

 (Figure 2). This concentration is about one- 

 twentieth of the concentration (50 ppb) that 

 caused retardation of growth in rainbow trout fry 

 that had been exposed continuously for about 67 d 

 from the beginning of the egg stage (Burkhalter 

 and Kaya 1977). Pink salmon alevins exposed to 

 NH3 for 61 d at 4° C in our study were more sensi- 

 tive (as judged by effects on size) than the faster 

 developing rainbow trout eggs and alevins ex- 

 posed for about 67 d at 12° C. In the trout study 

 (Burkhalter and Kaya 1977), 25 d of the 67-d expo- 

 sure were during the egg stage, a stage that is 

 relatively tolerant compared with the alevin 

 stage. 



The highest concentrations of NH3 in the dis- 

 charge water of a hatchery incubator with an ab- 

 normally high density of pink salmon alevins 

 (Bailey et al. 1980) was 0.14 ppb, and the highest 

 concentration from intragravel water of a stream 



