T. Penczak

THE ENRICHMENT OF A MESOTROPHIC LAKE BY CARBON, PHOSPHORUS AND NITROGEN FROM THE CAGE AQUACULTURE OF RAINBOW TROUT, SALMO GAIRDNERI

(1) The cage aquaculture of rainbow trout, Salmo gairdneri Richardson, enriched the mesotrophic Glebokie Lake with carbon, phosphorus and nitrogen. (2) Two generations were studied, from their introduction to the cages as 0 group trout in June until their removal as marketable trout in the Autumn of the following year. (3) An inter-generation budget of energy and bioelements (C, P, N) showed that, for every kilogram of marketable trout produced, the lake was enriched by 0.75 kg C, 0 023 kg P and 0.10 kg N (27-91, 0.84 and 3.58 g m-2 yr-1 respectively). This eutrophication is expected to cause the loss of the natural populations of Coregonidae. (4) The values of K1, K2 and U-1 showed that harvesting trout in Summer and Autumn does not make full use of the high utilization of food during those periods; it is suggested that harvesting should occur in October and November.

A long-term study (1985–1995) of fish populations in the impounded Warta River, Poland

Three sites, two in the tailwater and one upstream of the backwater of a large man-made reservoir in the middle course of the 808 km long lowland Warta River (Oder catchment), were studied. The pre-impoundment study lasted one (1985), the post-impoundment one 10 yr (1986–1995). The dam contributed to the extinction of the anadromous Vimba vimba, and of the rheophilous Chondrostoma nasus, both cyprinids. A number of directly or indirectly negative changes related to the construction of the reservoir were recorded in the tailwater. These changes affected the species number, spawning groups, diversity, density, standing crop, mean body weight, ABC index, and proportional stock density – PSD. Numerous impacts related to engineering, water chemistry and climate were more negative for fish at the tailwater than at the backwater sites. The hydrology of the site upstream of the backwater continued to be dependent on natural factors. Fish populations there suffered only from accidental impacts of the construction of the dam, such as bank revetment or the clearance of trees and shrubs.

Fish diversity and community structure in two small tributaries of the Paraná River, Paraná State, Brazil

In eleven sites on two small tributaries of the Paraná River (North-West Paraná State), 6.8 and 4.0 km in length, 1263 fish specimens of 28 taxons and 14 families were collected using electrofishing. Up to twelve years ago the catchments of the two rivers were covered by tropical jungle; this has now been replaced by pasture and arable fields. Mean diversity indices of Simpson and Shannon indices were close to 0.6, which would indicate that human impact affected fish populations although the river beds have retained their original shape, except cleared of riparian trees. Despite their close location (about 18 km), the two streams differed from each other in their fish faunal composition. The distinctive nature of the fish communities in the two streams was a result of: conductivity, pH, also hiding places, riparian vegetation, submerged macrophytes and depth and width of the rivers.

Applicability of the abundance/biomass comparison method for detecting human impacts on fish populations in the Pilica River, Poland

In the Pilica River, a tributary of the Vistula, the abundance/biomass comparison method was employed for assessing the impact of stresses on fish populations. Generally, the method proved a useful tool for estimating disturbances in fish communities caused by point source sewage inputs and all impacts of a dam. A high correlation was recorded between the ABC index and Simpson and Shannon indices, which also negatively respond to the investigated stresses.

Populations and production of fish in two small tributaries of the Paraná River, Paraná, Brazil

Mean biomass (153-1) and production (P) of fish in two small tributaries of the Paraná River (Paraná, Brazil) were 61 kg ha−1 and 48 kg ha−1 yr−1 in the Caracu River and 29 kg ha−1 and 26 kg ha−1 yr−1 in the Agua do Rancho River, respectively. Matrix correlation analysis revealed high positive correlations of both 153-2 and P to maximum depth and hiding places and, at a lower level of significance, to mean depth, pH and oxygen level. Lower 153-3 and P values were found in the Agua do Rancho River, whose valley has retained a more natural character, rich canopy and scarcity of macrophytes, but also lower conductivity and nitrogen and phosphate levels than those in the Caracu River.

Food consumption and energy transformations by fish populations in two small lowland rivers in Poland

The food consumption of all fish species was estimated at nine sites in two lowland rivers. The fish populations, whose diet consisted chiefly of invertebrates (88%), used on the average 9.88 (7.14–13.3) kg of invertebrates for the production of 1 kg of fish flesh. This number of invertebrates corresponds to 39.35 ± 7.34 MJ (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\] ± S.D.). In estimating the effective use of consumed (K1) and assimilated (K2) food for growth, it was found that the predominance of food of animal origin over plant of detrital food resulted in a decrease in the living cost (maintenance ration) of fish.

Problems of estimating population parameters and production of fish in a tropical rain forest stream, North Venezuela

The River Todasana is a small rain tropical forest stream emptying to the Caribbean Sea (Venezuela). Fish were sampled by electrofishing at three contiguous sites (pool, riffle, raceway). Nine species were recorded. Their mean biomass and production were: 43.72 kg ha−1 and 36.94 kg ha−1 yr−1, maximum: 55.47 kg ha−1 and 42.33 kg ha−1 yr−1, respectively.

Effects of removal and regeneration of bankside vegetation on fish population dynamics in the Warta River, Poland

In March 1989 both banks of a 450 m section of the Warta River, 2 km above a reservoir, were cleared of their riparian vegetation (osiers, willows and alders). In October 1988 17 fish species had been recorded there, with a standing crop (SC) of 31.9 kg ha −1. In April 1989, the number of species decreased to 11, and their SC to 7.9 kg ha −1.

The importance of qualitative inventory sampling using electric fishing and nets in a large, tropical river (Brazil)

Qualitative fish sampling (single catch) using three methods (electric fishing, gillnets, seine nets) was assessed at three sites in the Ivai River (Paraná State, Brazil) to check their usefulness for quick inventory investigations. Electric fishing at a constant effort (15 min per each) was considered to be the best sampling technique. Taxon richness was calculated as the expected number of species using a rarefraction technique. Samples of 300–325 individuals, and 6–10 repetitions in neighbouring segments were sufficient. Even though electric fishing was conducted with the same effort in similar segments at each site there were many differences in species abundance. This suggests that the estimated fish specimen number obtained with constant effort is of limited validity on one sampling occasion and may be best considered as an ‘index of density’ only. The differences may partially be caused by the segments being located along the right and left bank of the large river (problem of different habitats). Qualitative and quantitative differences between electric fishing, gill-netting and seine-netting samples were very high at a high significance level. Nevertheless, as 22.4% taxa were caught only by gill or seine nets, these gears were important for complementing the species list.

Contribution of bream, Abramis brama (L.), to the nutrient dynamics of Lake Balaton

Dry matter, total carbon (C), nitrogen (N) and phosphorus (P) content of mature bream from Lake Balaton were investigated and the quantities of N and P stored in the bream population and their possible removal by fishery were estimated. Carbon made up 43.3–44.8% of dry weight, N made up on average 10.6% of the dry weight of bream and P accounted for a further 2.7%. About 3.3 kg N ha−1 and 0.9 kg P ha−l are stored in the bream population. Approximately 0.5 kg N ha−1 and 0.1 kg P ha−1 are removed from the lake by bream harvest. Taking into account the total fish yield, the N removal is 2.1% and P removal 3.4% of the amount entering the lake.