Adverse effects of 23 bypass‐ or mill stream‐type small hydropower stations (SHPSs) have been studied by traditional benthological and ichthyological techniques. Four locations, if available, were distinguished for each SHPS: the natural flow sections (NFS) above and below the SHPS area, the mill stream or diversion channel bringing water to the turbine, and the reduced discharge section (RDS) of the former stream course. Most SHPSs took a high percentage of the stream discharge (turbine intake capacity was usually bigger than average yearly discharge of the stream at a given point). Despite this, the decrease in the stream‐wetted area was relatively low (usually 0–30%). The changes of benthic communities did not show any distinct trend explicable by the SHPS operation. Mechanical damage of fish by turbines was found rather rarely with SHPSs. The diverting weir (which usually distributes the discharge between the RDS and the mill stream), in combination with the abstraction of water for SHPSs, was an important migration barrier for resident fish in 30% of SHPSs. Water abstraction causes succession from large‐bodied fish species (adult brown trout, chub, dace, grayling, etc.) towards small‐bodied fish (trout fry, minnow, bullhead, stone loach, gudgeon). Average individual weight and fish biomass decreased four times in RDSs. Fish biomass losses exhibit significant negative relationships to the ratio of turbine intake capacity and stream discharge. Several mitigation measures are suggested. © 1997 John Wiley & Sons, Ltd.

Supplemental cereal feeding (maize, wheat and triticale compared with a control group with natural food only) and its effect on fatty acid (FA) expression in the flesh during long-lasting storage of common carp (Cyprinus carpio) was investigated. The fish were cultured in earthen ponds in the Trebon region (Czech Republic). The content of fatty acid was investigated in the flesh of carp during 8 months oflong-lasting storage without additional feeding. Sixty common carp in their third year of life were used for the analyses. The weight of the fish (marketable fish) ranged from 1,358 g to 2,221 g. Polyunsaturated fatty acid (PUFA, n-3) content and composition in fish flesh were determined by gas chromatography (VARIAN 3300). Supplemental cereals caused lower levels of PUFAs and n-3 PUFAs in fish fat. The content of these fatty acids did not decrease, even during 8 months of fish storage. The average percentage of PUFAs in total fat from edible parts was: for maize 13.7% ± 1.58%, for wheat 11.6% ± 1.17% and for triticale 10.7% ± 1.00%. The percentage of n-3 PUFA for maize was 2.5% ± 0.36%, for wheat 3.38% ± 0.44% and for triticale 3.1% ± 0.39%.

The aim of the work was to measure and confirm changes in the qualitative properties of frozen carp flesh (Cyprinus carpio L.) during 84 days of storage at -20 • C, using instrumental texture profile analysis focused on hardness, cohesiveness, and springiness. Hardness in fresh fish was 2.908 N, in fish stored 28 days 1.238 N, after 56 days 0.505 N, and after 84 days 0.491 N. Cohesiveness (dimensionless unit) in fresh fish was 0.838, after 28 days 0.740, after 56 days 0.720, and after 84 days 0.712. Springiness (dimensionless unit) in fresh fish was 0.682, after 28 days 0.625, after 56 days 0.577, and at 84 days of storage 0.534. The texture profile analysis effect was determined by several regression and linear models. It is possible to calculate a certain time period in which changes develop up to the level of 50% of deterioration-in hardness 17.5 days and in cohesiveness 12.9 days, as this was proven to a defined significance level (P > 0.01). Only changes in springiness showed a linear regression in the level of 0.002 (rounded) for each day. Studies showed that the intensity of the most important changes in instrumental textural properties occurred during the initial 56 days after freezing and after up to 84 days of storage the changes continued at a lesser rate.

Effects of supplemental feeding with cereals (rye, triticale, maize and the unsupplemental control group) on fat content in flesh of 3‐year‐old common carp (Cyprinus carpio) were the subject of study carried out at four ponds (Czech Republic, Central Europe) during the growing season. The main result was that supplemental feeding with cereals to the same energetic level was associated with varying growth and fat content in the flesh of common carp. At the end of the experiment, the stock of fish supplementally fed with maize was found to have the highest fat content (112.7 ± 15.6 g kg−1), while the lowest value of fat content was found in the control group (56.8 ± 9.4 g kg−1). The carps supplementally fed with rye were found to have a higher fat content (90.1 ± 19.0) than those supplementally fed with triticale (84.3 ± 15.7 g kg−1). Established average fat content values (except for maize) were at the level that indicate a high sensory quality of carp flesh during the whole growing season.

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