Hatching, growth, major ion concentrations, and ostelogical development of Brook trout (Salvelinus fontinalis) alevins exposed to soft, acidic water
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Brook trout (Salvelinus fontirtalis) eyed-eggs and fry were continuously exposed (< 72 days) to 3 pH levels (5.0, 6.5, 7.2) in soft (0.10 meq/L total hardness), low alkaline (< 0.14 meq/L) , 10 degree Celcius water to determine effects of reduced pH on hatching success, growth, major whole-body ion concentrations, and osteological development in Ca+2 depleted water. Hatching success was observed daily and the date of 50% hatch was established for each treatment. Fish were fed an excess of a low Ca+2 diet after the completion of yolk absorption and initiation of swim-up behavior. This diet was replaced 1 week later with freshly hatched brine shrimp nauplii. Subsamples of fish were taken from each treatment at regular intervals over a 45-day period following median hatch. Some fish were individually dried and weighed to assess growth, then analyzed to determine whole-body Na+, K+, Ca+2, Mg+2 , and Cl- concentrations. In other fish, mineralized bone tissue was stained and objectively examined to assess the progression of ossification. In comparison to fish in the control (pH 7.2) treatment, more time was required for pH 5.0-treated fish to achieve median hatch and for both the pH 6.5- and pH 5.0-treated fish to complete hatching. Cumulative hatching success was reduced at pH 5.0 and pH 6.5. Hatching success followed a normal distribution at pH 7.2 but became increasingly skewed at lower pH levels. Patterns of growth were similar among fish from all treatments. Dry weight decreased during yolk absorption but was unaffected by exposure to reduced pH. Dry weight increased rapidly during exogenous feeding, particularly as the fish fed on brine shrimp nauplii. Significant differences in growth among treatments at this time were probably due to differences in availability of food rather than pH. Whole-body Na+, K+, Ca+2 , and Cl- concentrations of fish exposed to pH 5.0 were less than those of fish exposed to the circumneutral pH treatments throughout most of yolk absorption and early exogenous feeding. Only the reduction in whole-body Na+ concentrations followed a consistent pH relationship. Patterns of whole-body ion accumulation were similar among fish from all treatments during most of the exposure. The pattern of Ca+2 accumulation among fish in the pH 5.0 treatment was inconsistent during yolk absorption however, suggesting that reduced pH will alter normal Ca+2 accumulation at this time. The progression of ossification in the dentary-articular complex, branchiostegal rays, caudal epurals and hypurals, dorsal pterygiophores, pelvic basipterygia, and vertebral centra was substantially delayed by exposure to soft, acidified water. Osteological development comparable to that of fish in neutral pH waters was achieved within 9 days for most structures. The criteria used to assess osteological development were sensitive enough to distinguish more than 68% of the individuals exposed to acidic water from those exposed to circumneutral pH waters during early yolk absorption and later when exogenous feeding was well established.
Acid rain -- Environmental aspects