uon TPigure 3) The process is insidious and e been cited as the on yield are oft
ID: 803347 • Letter: U
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uon TPigure 3) The process is insidious and e been cited as the on yield are oftem delayed and not recognizable until the popu- eading to the gradual extinction of fish popu- lation is close to extinction. This is particularly true for late- lations in all of the studies conducted to date in the countries maturing species with great longevity observations of changes in population structure over time whicha clude decreased population density, a shift in t Recruitment failure may occur as a resalt of acid-induced reased population density, a shift in the size and age in egg deposition. Decreased ege deposition can occur as a structure of the population to one comsisting primarily of older resalt of either disrupted spawning behavior (22, 25) or affects and larger fish, and even increased growth rates in some cases. on reproductive physiology in maturing adults (16). The late ment failure in fish populations of the Sudbury area lakes in Ontario, Canada (16). Specifically, females of several spe- Figure 1. Frequency distrbution of pH and fish population tatus in cies collected after their normal spawning perilods w Adirondack Mountaln lakes meters elevation. Fish populat elevation. Piah populs- not to have released their ova. These fish also exhibited ab- by sarvey gl netting euring the sunmer of 197s. normally low serum calcium levels during the perio of on an tion stat determined by survey g netting during the ummer of 1971 y low serum calcium levels during the period of ovarian maturation and the authors suggested that a disruption in female repeoductive physiology. This effect has not yet been reported elsewhere and studies conducted in Norway (9) Sweden (II), and the United States (20) swggest that eges and newly hatched larvae are the most vulnerable periods of de velopment Observed cases of reproductive failure have bcen mostly atträbuted to acid-induced mortality of eggs and fry in these latter studies CAUSE OF FISH DEATH tality of fis The physiological mechanisms involved in acid-induced mor h may vary in response to different levels of acidity f synergistice components (ee heavy metals, carbon dioxide). At very low pt levels (less than pH 3) co ce of synergistic pH may be the primary cause of death (25), however these low pH levels are rarely encountered in the acidified lakes and streams of concern. At the less acute levels (pH 4 5) en countered in these waters, disturbance of normal ion and NO FISH PRESENT FISH PRESENT Laboratory and field studies conducted recently in Norway (1, 7) strongly support this hypothesis and further demonstrate Figure 2. Froquency distribution of pH ish Adironteek lakes g perlad 1928-1937 and again In 1975 datr bution of pH nsh poplation statu·in 'orty the significance of the total salt content of the water as greater than 610 meters elevation, surveyed during the factor affecting acid tolerance. Laboratory experiments ducted with several species of salmonids demonstrate that sodium uptake is inhibited in water of low pH and salinity (1, 26) and that increasing salt concentrations effectively lower the lethal pt level (1, 20) This is in line with field obser- " a. The emecis oftheoretical nerease n mortality at age 0 on annual yield from a brook trout popalation, (Modised ater Jensen, 1971, Figure 1 INCREASE IN MORTALITY 10 1930's GENERATION NUMBER -50% NO FISH PRESENT FISH PRESENT 229 This content downloaded from 146111.183.47 on Tue, 22 Sep 2015 19 51:03 UTCExplanation / Answer
The lakes in the Adirondack mountains were analysed to find the relationship between fish mortality and the different acid levels of the levels. It was observed that a very low ph level less than 3, there was no fish population. The fish die because of the coagulation of mucus on the gill surface and the anoxia. Usually this condition of very low ph is rarely found in the lakes. At less acute levels i. 4-5 ph some fishes survive some die. The fish die because of disturbance in the normal ion and acid base balance. The salt content of water affect the tolerance of fish to acid. Since sodium uptake is inhibited in the water of low ph and increasing salt concentration can effectively increase the lethal ph level. The maximum population of fish is found in ph greater than 5 (5-7)
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