S. Summerfelt | USGS Science

USGS2007

Minimizing noise in fiberglass aquaculture tanks: Noise reduction potential of various retrofits

Equipment used in intensive aquaculture systems, such as pumps and blowers can produce underwater sound levels and frequencies within the range of fish hearing. The impacts of underwater noise on fish are not well known, but limited research suggests that subjecting fish to noise could result in impairment of the auditory system, reduced growth rates, and increased stress. Consequently, reducing sound in fish tanks could result in advantages for cultured species and increased productivity for the aquaculture industry. The objective of this study was to evaluate the noise reduction potential of various retrofits to fiberglass fish culture tanks. The following structural changes were applied to tanks to reduce underwater noise: (1) inlet piping was suspended to avoid contact with the tank, (2) effluent piping was disconnected from a common drain line, (3) effluent piping was insulated beneath tanks, and (4) tanks were elevated on cement blocks and seated on insulated padding. Four combinations of the aforementioned structural changes were evaluated in duplicate and two tanks were left unchanged as controls. Control tanks had sound levels of 120.6 dB re 1 ??Pa. Each retrofit contributed to a reduction of underwater sound. As structural changes were combined, a cumulative reduction in sound level was observed. Tanks designed with a combination of retrofits had sound levels of 108.6 dB re 1 ??Pa, a four-fold reduction in sound pressure level. Sound frequency spectra indicated that the greatest sound reductions occurred between 2 and 100 Hz and demonstrated that nearby pumps and blowers created tonal frequencies that were transmitted into the tanks. The tank modifications used during this study were simple and inexpensive and could be applied to existing systems or considered when designing aquaculture facilities. ?? 2007 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗

USGS2000

Toxicity of acidified chitosan for cultured rainbow trout (Oncorhynchus mykiss)

Chitosan is a deacetylation product of chitin. It is used as a flocculent for sewage and brewery wastes, and as a chelator of heavy metals. In aquaculture, chitosan has been used as an immunostimulant for protection against bacterial diseases in fish, for controlled release of vaccines, and as a diet supplement. Chitosan has generally been considered to be nontoxic to animals, but when it was dissolved in acetic acid and added to a culture system at 1.0 ppm to remove organic solids, we found acute toxicity to rainbow trout ( Oncorhynchus mykiss ). In controlled experiments to determine the extent of toxicity, we found that trout died after several hours exposure to 0.75 ppm and died in 24 h after exposure to 0.075 ppm. Exposure to 0.038 ppm resulted in mortality after 6 days exposure, while exposure to 0.019 ppm resulted in no mortality after 14 days exposure. Histological examination of gills, skin, muscle, and internal organs indicated significant and consistent pathological changes only in gills. Lifting of lamellar epithelium, hypertrophy and hyperplasia of lamellar epithelial cells occurred in trout exposed to 0.019 and 0.038 ppm. In trout exposed to 0.75 or 0.075 ppm chitosan, large areas of lamellar fusion were observed. These results show that soluble acidified chitosan is highly toxic to rainbow trout even at low concentrations.

Aquaculture↗