Effects of suspended solids concentration and particle size on survival and gill structure in fish

摘要

In this study, we experimentally examined the influence of high concentrations of suspended solids on ayu (Plecoglossus altivelis), rainbow trout (Oncorhynchus mykiss), and sculpin (Cottus pollux). Three experiments were carried out. In the first experiment 250 ayu were exposed to one of eight different particle sizes ranging in concentrations from 1, 500 to 15, 940 mg/L and the survival over a 24 h period was examined. In the second experiment 350 ayu were exposed to material consisting one of three different particle sizes ranging in concentrations from 560 to 20, 750 mg/L and the weight and size distribution of particles adhering to the gills were measured. In the third experiment 380 ayu, 90 rainbow trout, and 35 sculpin were exposed to one of six different particle sizes ranging in concentrations from 180 to 26, 200 mg/L and the gill structure was inspected. We found that the particle size distribution of material adhering to the gills differed from that of suspended solids in the exposure tanks. A comparison of the particle size distribution of particles adhering to the gills of surviving fish and dead fish indicated four stages leading to fish death. The diameter of particles adhering to the gills of ayu is ranged from 20 to 45 μm on which it is related to the amount of space between the gill filaments. By using particle size to correct the concentrations, we were able to determine 90% survival levels under different suspended solids concentrations and materials. The average filament width of ayu is significantly different from the two salmonids and sculpin which are more resistant to high concentrations of suspended solids compared to ayu. We assume that the space between ordinary filaments is the. main determining factor in the susceptibility of different species offish to suspended solids concentrations. Our results show that the survival of other spices of fish in highly turbid rivers can be also predicted by using corrected suspended solids concentrations; which can be determined for any range of particle sizes.