Fish are known for their high phenotypic plasticity in life‐history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade‐offs in phenotypic plasticity between life‐history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long‐term incubation experiments. The wild parental fish originated from four separate populations with markedly different densities, and hence naturally induced differences in their growth and fecundity. The energy allocation to somatic tissues and eggs prior to spawning served as a proxy for total resource availability to individual females, and its effects on offspring survival and growth were analyzed. Vendace females allocated a rather constant proportion of available energy to eggs (per body mass) despite different growth patterns depending on the total resources in the different lakes; investment into eggs thus dictated the share remaining for growth. The energy allocation to eggs per mass was higher in young than in old spawners and the egg size and the relative fecundity differed between them: Young females produced more and smaller eggs and larvae than old spawners. In contrast to earlier observations of salmonids, a shortage of maternal food resources did not increase offspring size and survival. Vendace females in sparse populations with ample resources and high growth produced larger eggs and larvae. Vendace accommodate strong population fluctuations by their high plasticity in growth and fecundity, which affect their offspring size and consequently their recruitment and productivity, and account for their persistence and resilience in the face of high fishing mortality.

Elevated concentrations of sulfate in waterways are observed due to various anthropogenic activities. Elevated levels of sulfate can have harmful effects on aquatic life in freshwaters: sulfate can cause osmotic stress or specific ion toxicity in aquatic organisms, especially in soft waters where Ca²⁺ and Mg²⁺ concentrations are low. Formerly, chronic toxicity test data in soft water have been scarce. The chronic and acute sulfate toxicity tests conducted with aquatic organisms from 10 families across various trophic levels in this study multiplied the number of tests conducted in soft freshwater conditions and enabled derivation of the species sensitivity distribution (SSD) and sulfate hazardous concentrations for soft freshwaters. The cladoceran Daphnia longispina and freshwater snail Lymnaea stagnalis were the most sensitive to sulfate among the studied species. Harmful effects on the reproduction of D. longispina were observed at 49 mg SO₄ /L while growth of L. stagnalis was inhibited at 217 mg SO₄ /L. Most studied organisms tolerated high sulfate concentrations: the median of chronic effective concentrations (EC10 or LC10) was 1008 mg/L for all the species tested in this study. Based on the species sensitivity distribution of the studied species the hazardous concentration for 5 % of aquatic organism (HC5) in soft waters was 117-194 mg SO₄/L. Different data set combinations were used to demonstrate the data variability in SSD-based HC5 estimates. The lowest values were produced from combining biotest results from the present study and earlier literature, while the highest values were calculated from the present study only. The derived chronic no-effect concentrations (PNEC) varied between 39 and 65 mg SO₄/L.

Sulfate occurs naturally in the aquatic environment but its elevated levels can be toxic to aquatic life in freshwater environments. We investigated the toxicity of sulfate in humic, soft freshwater to whitefish (Coregonus lavaretus) from fertilization of eggs to hatching i.e. during the critical phases of whitefish early development. Anadromous Kokemäenjoki whitefish eggs and sperm during fertilization, embryos and larvae were exposed in the long-term 175-day incubation to seven different sodium sulfate (Na₂SO₄) concentrations from 44 to 2 000 mg SO₄ L^-1. Endpoint variables were the fertilization success, offspring survival and larval growth. Egg fertilization and early embryonic development were the most sensitive developmental stages of whitefish to sulfate, although the fertilization success and survival of embryos decreased only in the highest concentration of 2 000 mg SO₄ L^-1. The survival during late embryonic period, hatching and the 5-day larval period was high and no difference between the control and sulfate treatments were observed. LC₅₀-values of sulfate for early embryonic period and for the entire embryonic and larval period was 1 413 and 1 161 mg L^-1, respectively. The NOEC (No-observed Effect Concentration) of sulfate for the both periods was 1 207 mg L^-1. The tolerance of whitefish early stages to sulfate toxicity seems to be on the same level as the tolerance of other salmonids' early stages.