Barry, Terence P.; Malison, Jeffrey A. (ed.) / Proceedings of PERCIS III, the Third International Percid Fish Symposium, University of Wisconsin, Madison, Wisconsin, U.S.A., July 20-24, 2003
(Ecology) Advantages of perch (Perca fluviatilis) seasonal migrations to brackish waters, pp. 77-78 PDF (1.2 MB)
ADVANTAGES OF PERCH (Percafluviatilis) SEASONAL MIGRATIONS TO BRACKISH WATERS. Linas Lozys, Laboratory of Marine Ecology, Institute 2600, Lithuania, lozys(dawekoi.lt Introduction. Perch (Percafluviatilis) are known as seasonally migrating fish species in southern part of the Baltic Sea. Perch inhabit brackish coastal waters of the southern Baltic in summer time, while they usually winter in the freshwater lagoons. The objective of the study was to explain experimentally perch spring migration behaviour while they migrate from the freshwater Curonian Lagoon to the brackish Baltic Sea, Lithuania, and to prove a cause of their backward migration to the Lagoon in the autumn. Methods. Field study. Material for the perch in situ growth study was collected during 1998 - 2000, in September when growth in length' and accumulation of energy resources reached the yearly maximum. The growth study focused on perch individuals of 1997-year class, since this generation dominated in both water bodies: individuals of the other age groups were scarce. All perch were weighed (± 1.0 g) and measured (total length L, ± 0.5 cm). Condition factor (CF) and fatness coefficient (Kf) were calculated as follows (Bagenal & Tesch, 1978; Bukelskis & Kublickas, 1988): CF = W/L3 X 100, where W, body weight in grams, L, total length in cm and KF = w / W x 100, where w, weight of fat on the intestines, in grams, W, body weight, in grams. Since differences in the growth rate of perch for the same age group is considerable, the parameters were calculated for the same length, but different age perch individuals. Both sexes were combined in calculations. Fat content (CF) in muscle tissues was expressed as a percentage of wet weight. Perch age was estimated from growth zones of opercular bones. Only females were aged. For statistical analysis t-tests was used. Experimental study of growth. To evaluate the effect of salinity on perch growth, a survey of perch YOY growth under different salinity conditions was conducted. The first experiment was performed at "high temperature" range (mean water temperature 19.2) and the second - at "low temperature" range (mean water temperature 12.4). Available laboratory facilities restricted the experiment to YOY providing sufficient density of fish for statistical analysis. Perch YOY were collected by seine netting at Vente cape, a coastal area in the eastern part of the Curonian Lagoon (55°21' N, 21°12' E) in August 2001 and 2002. After 5 days acclimatization in fresh water, fish were randomly divided into 15 experimental groups. Each group comprised 10 fish, which were reared in identical 100-1 glass aquaria under continuous aeration. The influence of salinity on the perch growth was studied under certain three experimental salinity conditions: five aquaria contained water at 5 ppt, five at 2 ppt and five contained fresh water. The duration of the experiment in "high temperature" range was three weeks, while the duration of the experiment in "low temperature" range was six weeks. Water temperature was ambient in all aquaria and during the experimental period, fluctuated from 24.9 to 16.00C in "high temperature" range, while in of Ecology, Vilnius University, Akademijos st. 2, Vilnius "low temperature" range - from 14.1 to 11.70C. All fish were provided with the same quantity of live Chironomus spp. larvae, weighed with accuracy of 0.01 g. To ensure similar food consumption between replicates, each new portion of food was introduced immediately following consumption of the previous ration. Total weight (±0.01 g, after excess water removed) for each replicate was measured prior to the beginning of the experiment and after each week. To assess differences in growth under different treatments, the weight increments of perch YOY groups of each replicate were analysed using Tukey honest significant difference test. Results. Perch start to migrate from the Curonian Lagoon after wintering and spawning. Field observations demonstrated better growth in length and condition (Fig. 2, 3) in the sea despite lower water temperature (Fig 1). 24 22 20 () 18 - 16 0 &- 14 4 12 o 10 E8 0 6 4 2 w IV V V Vi VII KX Month Figure 1. Water temperatures in the Curonian Lagoon (-) and the Baltic Sea (A) during March - September 1998-2000 (vertical bars represent 1 SD). E U 0 -a I- 1998 1999 2000 1+ 2+ 3+ Figure 2. The total length of perch of 1997 year class in the Curonian Lagoon (i) and the Baltic Sea (A) during September of 1998-2000 (vertical bars represent 1 SD) (Lozys 2001). The results of the experiment in "high temperature" range demonstrated the significant affect of salinity on YOY perch growth at both 5 and 2 ppt salinity conditions (Fig. 4) (Lo'ys, in press). Differences in growth between 2 and 5 ppt salinity replicates were insignificant. Salinity affect was insignificant at the "low temperature" range (Fig. 5). 77 I I. I , , I I' t I I i' I I I I 24, 22_ 20 I 18 16 14 12 TI ICI I . 0 I I ... I . I V.
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