Larvae of parasitic European river lamprey (Lampetra fluviatilis) were studied in the Kalajoki, Pyhäjoki, and Siikajoki rivers which flow into Bothnian Bay in Finland. In the Kalajoki river, ammocoetes occur up to 40 km upstream from the mouth, but in the Pyhäjoki rapids block most of the adult migration about 20 km from the river mouth. The Siikajoki river is blocked by a hydroelectric dam 16 km from the estuary. The mean abundance of larvae in 1977 was 12/m2 in the Pyhäjoki and 21/m2 in the Siikajoki river. In 1978 the mean abundance was 6/m2 in the best area (an 8-km stretch) of the Kalajoki, 15/m2 in the Pyhajoki, and 21/m2 in the lower 7 km of the Siikajoki river. The mean length of larvae was smallest in the Siikajoki (45 mm in 1977 and 55 mm in 1978) and largest in the Kalajoki river (77 mm in 1978). Reasons for such size differences and the variation in year-class strengths may be attributable to oxygen deficiencies and other problems caused by dams and other construction work on the rivers. Both the Siikajoki and Kalajoki rivers appear to be affected in this way. The Pyhäjoki appears to be the least disturbed of the three rivers. Ammocoetes favor mean grain sizes from 0.05 to 0.10 mm. Myomere studies on larvae from the Siikajoki river gave a mean count of 62.3 (range, 60–64) and verified that the larvae involved were those of the river lamprey.Key words: lamprey, Finland, larvae, ammocoete, Lampetra fluviatilis, European river lamprey

The coastal region of Bothnian Bay is now the center of fisheries for European river lamprey Lampetra fluviatilis in Finland. This species has been studied in the Kalajoki and Pyhäjoki rivers and data are also available from the Lestijoki River. In the Kalajoki River in 1977, 30 fishermen operating 70 trap nets and 900 basket traps caught about 134 000 lampreys. Fewer traps were used by a smaller number of fishermen in 1978, but the catch remained the same. In the Pyhäjoki River in 1977, 50 fishermen operating 50 trap nets and 330 basket traps caught 184 000 lampreys. In 1978 fewer traps were used by a smaller number of fishermen and the catch was 93 000 lampreys. Tagging indicated that about 80% of the upstream migrants (estimated at 200 000 in 1977) were being captured in the Kalajoki River, but only about 65% in the Pyhajoki River (estimated at 400 000 – 500 000 in 1977). Reasons for the differences between rivers and years are discussed.Key words: Lampetra fluviatilis, Finland, fishery, rivers

Changes in total activity, heart and ventilation rates were observed in 2‐year‐old brown trout, following handling stress, using non‐contact bioelectronic monitoring equipment. Experiments were carried out in laboratory conditions at water temperatures below 4° C, Transfer between tanks as well as 5 min restraint stress increased the total activity of fish for 24 to 48 h, after which it declined to near the pre‐stress level. The transfer and struggle both elevated the heart rate for 3 to 4 days. Ventilation rate was elevated to a maximum of about 30% above the nominal level and recovered within 3 to 4 days. Both heart and ventilation rates were higher in feeding fish relative to fasting fish after stress and rates remained higher throughout a 7 day period of recovery. A diel rhythm of lower rates during the night appeared in both heart and ventilation rates within 3 to 4 days after handling stress.

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Abstract— The wintering success of young‐of‐the‐year pikeperches (Stizostedion lucioperca) was examined in the laboratory during the winter of 1993‐1994. From September to November half the fishes were offered artificial fishfood; the others received plankton with river water. Pikeperch did not eat the fishfood properly, and poorer condition of the smallest fish fed artificially was reflected in a lower amount of lipid in the whole fish at the beginning of the experiment in November. The autumnal diet played an important role in determining the wintering success even when the effect of size was removed. In contrast, feeding during the experiment did not affect survival. However, feeding fishes had more lipid at the end of the experiment in April than starved ones and their protein content also increased during the winter.