Pike Larvae Research Articles

Experience of reproduction of pike (Esox lucius Linnaeus, 1758) using the factory method

The article is devoted to the conducted experience of reproduction of the common pike (Esox lucius Linnaeus, 1758) in the conditions of industrial fish farming. Pike is an important object of aquaculture, used for biomelioration of reservoirs and for amateur fishing. The purpose of this work was to obtain pike larvae by the factory method with a different method of incubation of eggs. To obtain sexual products, pike producers were selected, after bonification they were landed in pools on a direct-flow system. Eggs from females were obtained by pumping, into enameled containers separately for each individual, sperm from males was obtained by slaughtering. After fertilization, the eggs were de-glued and placed in a Weiss apparatus for incubation, a total of 23.75 million pieces of eggs were obtained, the average fertility of females was 25 thousand eggs, the percentage of fertilization was 70%. To conduct the experiment, the eggs were divided into two parts, the group was left for incubation in Weiss devices. Group II at the 22nd stage of development, the “pigmented eye stage”, was placed on frames with a mosquito net of a smaller diameter measuring 0.5 by 0.5 m, with a side height of 1.5 cm in the ICA-2 pools. In the group I at the 24th stage of eggs development, hatching occurred, the survival rate of the larva was 27.3%, in the group II, hatching was 40.8%. At the stage before the transition to active nutrition, the larvae were collected in polyethylene transport bags with oxygen and released into a natural reservoir. Transportation was carried out at 12 degrees, at 2000 pcs/l.

Effects of weaning time, light regime, and stocking density on growth, condition, survival, and cannibalism rates in northern pike (Esox lucius L.) larvae and early juveniles under intensive culture

In this study, three separate experiments were conducted to optimize the intensive larviculture of pike (Esox lucius L.) under different weaning times, light regimes, and stocking densities. In the first experiment, larvae were fed sequential combinations of live feed (LF), co-feeding with dry starter (DS), and only DS feed for 18 days as follows: 9 days LF followed by 3 days co-feeding and 5 days DS (group A); 6 days LF followed by 3 days co-feeding and 9 days DS (group B); 3 days LF followed by 3 days co-feeding and 12 days DS (group C); and DS alone for 18 days (group D). Fish fed LF had significantly higher growth rates than those fed a dry diet (p< 0.05). Extending the feeding period on LF resulted in a significantly higher growth rate (24.6% d−1), variability (13.5%), and heterogeneity (299.5% d−1) than fish fed a DS. In the second experiment, the effect of the light regime was assessed at eight different levels (L0:D24; L24:D0; L16:D8; L4:D4:L4:D4:L4:D4; L8:D4:L8:D4; L12:D12; L8:D16; and L4:D8:L4:D8). The growth and survival of the larvae increased with increasing light period. Groups exposed to complete light (L24:D0) and 16 h of light (L16:D8) exhibited significantly higher weight gain and specific growth rate (SGR, %) than the other groups. The highest survival was observed in fish reared with complete light (68.5 ± 4.5%) and an L8:D4:L8:D4 light regime (61.4 ± 5.2%). All larvae maintained under L0:D24 died during the experiment. The third experiment tested the effect of the fish density within four experimental groups: 10 ind L−1, 20 ind L−1, 40 ind L−1, and 80 ind L−1. Fish at densities of 20 and 40 ind L−1 had significantly higher weight gain and SGR (%) than those in the other groups. The highest survival was in fish reared with 20 ind L−1 density (72.5 ± 8.5%). Fish at densities of 10 and 80 ind L−1 showed significantly higher cannibalism rates than those in the other groups. These results indicated that weaning time, photoperiod, and stocking density play significant roles in early pike larval performance.

The role of chemical communication in the predator-prey role reversal of northern pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus)

Predator-prey interactions can modify population dynamics and influence ecosystem functioning. An interesting, but less understood, aspect of such species interactions is predator-prey role reversal where a mesopredator can reduce the recruitment success, and ultimately the abundance, of their own predator. Such role reversal is ongoing in the Baltic Sea where increasing abundances of mesopredatory sticklebacks (Gasterosteus aculeatus) have resulted in intense predation on the recruits of their predator the northern pike (Esox lucius). Still, the mechanistic underpinning of this reversal remains poorly understood. Here we investigate the role of chemical communication in this predator-prey role reversal with the aim to understand whether and how sticklebacks use olfactory cues to assess whether pike constitutes a predator or prey. By performing a laboratory preference experiment, we show that chemical communication is indeed used by sticklebacks for assessing the predation risk emanated by adult pike but that it requires additional alarm cues (Schreckstoff) informing that sticklebacks are predated upon. Adult pike kairomones or alarm cues alone did not result in any adaptive response by sticklebacks nor did olfactory cues of pike as prey (pike larvae kairomones and dietary cues of zooplankton). This knowledge contributes to the understanding of predator-prey interactions as well as the dynamics of the shifting coastal fish community in the Baltic Sea. The results also suggest that addition of Schreckstoff to confined pike (and perch) spawning and recruitment habitats may deter sticklebacks from entering which should be further explored by management.

The more sheltered, the better – Coastal bays and lagoons are important reproduction habitats for pike in the northern Baltic Sea

The Quark Archipelago, in the northernmost part of the Baltic Sea, provides valuable reproduction areas for coastal fish such as pike (Esox lucius L.). Here, pike stocks are still in good condition compared to the southern Baltic Sea, where pike stocks have declined. Hence, this area offers a unique opportunity to study the underlying causes of successful pike reproduction and to identify a productive pike reproduction habitat. This study suggests that the key factor defining suitable reproduction habitats for pike in the Quark Archipelago was the level of shelter. The more sheltered a habitat, in terms of morphology and level of isolation of the site and the site's exposure to wave action and shoreline density, the better the reproduction habitat was for pike. Gloes, which are the most isolated successional stages of coastal lagoons, represented the most sheltered habitat type and showed the highest pike larvae abundance. Additionally, sheltered bays and flads, less isolated successional stages of coastal lagoons compared to gloes, were also used as reproduction habitats by pike but with a lower abundance of larvae compared to the gloes. Gradually increasing salinity and the occurrence of sticklebacks (Gasterosteidae) reflected the morphology of the site. Pike larvae were observed in locations without sticklebacks and with low salinity. Pike larvae were found mostly amongst fallen reed (Phragmites australis) and in areas with moss (Fontinalis sp.) growth, which supports earlier findings. This study provides valuable new knowledge on larval pike habitats and highlights the significance of sheltered bays and gloes in the northern Baltic Sea. The information can be utilised for planning conservation and the restoration of pike reproduction habitats to protect and restore pike populations on both a regional and larger scale.

Опыт термического мечения отолитов личинок щуки обыкновенной

The article provides a detailed review of the marking methods of juvenile fish and discusses the mechanisms of the microstructure pike otoliths’ formation. The feasibility of thermal otolith marking of larvae and early juvenile fish with a short period of embryonic development is shown on the example of the common pike. The objectives of the study were to determine the most suitable age of pike juveniles for marking, and the optimal duration of temperature exposure. Three marking protocols were tested, in which the water temperature gradient was 7-12 °C, and the exposure time was 5, 6 and 10 hours, respectively. The pike larvae were marked at the age of 4 days and 11 days (after the start of the exogenous feeding) at least four times. The results of marking were evaluated on the first day and on the 10 th day after marking, as well as at later stages of development (in the age of 21-44 days). Most visible marks were noted in short heating cycles (5-6 hours) in larvae before the start of the exogenous feeding.

Positive temperature effects on the initiation and intensity of cannibalistic behaviour of larval pike, Esox lucius L. Is cannibalism reflected in otolith fluctuating asymmetry?

Cannibalism can be a significant factor limiting the survival of pike, Esox lucius, early life stages in both natural and aquaculture conditions. In the present research, type I cannibalism was studied in pike larvae (size range: 9–32.5 mm standard length, SL) in controlled conditions for 45 days post-hatching (dph). For this purpose, the occurrence of cannibalistic pairs, i.e. prey caught by a cannibal inside the cannibal’s mouth, was monitored for 15 min periods by two observers six times daily. Cannibalism was not observed in fish that still had yolk-sacs, but it did occur as soon as the yolk-sac was absorbed on 5 dph at a body size of 13 mm at 22 °C and 10 dph at a body size of 13.4 mm at 15 °C. The ratio of prey to predator size was on average 87%, but the smallest observed size difference was only 1.3%. The intensity of cannibalistic attacks depended on water temperature with more intense cannibalism at 22 °C than at 15 °C, and no cannibalism at 10 °C. Fluctuating asymmetry (FA) in all three sagittal otolith size parameters (area, width, and length) was higher in prey than in cannibals, the differences were not statistically significant.

Predator-prey role reversal may impair the recovery of declining pike populations.

Many fish populations have experienced declines in recent decades due to anthropogenic disturbances, such as overfishing and habitat exploitation. Despite management actions, many populations show a limited capacity to recover. This may be attributed to reversal of predator-prey roles, yet empirical evidence to that effect remains scarce. Here, we combine field and laboratory studies to investigate the interaction between pike (Esox lucius), a large keystone top predatory fish, and the small-bodied mesopredatory threespine stickleback (Gasterosteus aculeatus) in the Baltic Sea where pike populations have declined. Our data suggest that stickleback predation on pike larvae depletes a large proportion of the recruitment and influences the size distribution through size-selective predation, which is corroborated by a gape-limitation experiment and diet analysis of wild-captured sticklebacks. The effects of stickleback predation are present across several populations and years, and our data suggest that early arrival of sticklebacks has stronger effects on juvenile pike survival. Finally, we use data on pike gape-limitation and the size distribution of sticklebacks to illustrate the process of role reversal. These findings suggest that mesopredator behaviour can reduce recruitment of a top predator species and impair the capacity of populations to recover. This emphasizes predator-prey role reversal as an important ecological and evolutionary driver that influences the outcome of restoration and management actions.

Prey selection by larval northern pike (Esox lucius) exposed to different zooplankton assemblages representing seasonally flooded wetland and nearshore bay habitats

AbstractA prey selection experiment was designed to investigate whether northern pike larvae, at swim‐up and advanced stages, select similar zooplankton prey in seasonally flooded wetlands and nearshore littoral zones, which represent primary St. Lawrence River northern pike spawning habitats. At first exogenous feeding, naïve swim‐up larvae exposed to both wetland and nearshore zooplankton were generalist consumers, feeding primarily on cyclopoid copepods and small cladocerans. No positive selection was observed for any prey taxa. Advanced larvae began to exhibit positive selection for large cladocerans. Significantly larger‐sized prey were consumed by advanced larvae given wetland vs. nearshore zooplankton. Large cladocerans made up a greater proportion of the assemblage originating from seasonally flooded wetlands vs. nearshore habitats, and may explain the difference in size selectivity. Our laboratory experiment suggests pike hatched in wetland environments have greater access to preferred, large cladoceran prey, and differences in spatial and temporal spawning distributions may have important implications for zooplankton availability and hence food consumption during the critical larval period.

Effect of static magnetic field on the hatching success, growth, mortality, and yolk-sac absorption of larval Northern pike Esox lucius

The effect of anthropogenic magnetic field on water ecosystems has been constantly growing as a result of an increasing number of underwater cables transferring electric current. Northern pike were subjected to a static magnetic field (emitted by DC cables) of 10 milliteslas (mT) during the embryonic phase and in the first six days post-hatching (DPH), in the period when larvae of this species in the natural environment are attached to artificial substrate. No statistically significant effect of a magnetic field was recorded on the hatching success (87.1% in the magnetic field and 83.3% in the control) or on larvae mortality (54.5% in magnetic field and 54.3% in control). The size of larvae at hatching (9.84 mm SL in a magnetic field and 9.86 mm SL in a control) and their growth rate during the first six days of life (0.52 mm·day−1 in a magnetic field and 0.53 mm·day−1 in a control) were also almost the same – no statistically significant differences. A significant effect of a magnetic field, however, was observed on the time of hatching (one day earlier in a magnetic field than in a control), yolk-sac size on 1 DPH (smaller in a magnetic field), and yolk-sac absorption time (faster in a magnetic field). Faster yolk-sac absorption time in a magnetic field was interpreted as an indication of increased metabolic rate. Even if some negative consequences may be expected as a result of shorter time until first feeding, the actual risk for increased Northern pike larvae mortality due to those factors seems to be negligible. Although it cannot be excluded that higher than 10 mT magnetic field values are hazardous for fish larvae, such values do not occur in the natural environment (e.g. along underwater cables).

The effect of hatching time on the bioenergetics of northern pike (Esox lucius) larvae from a single egg batch during the endogenous feeding period.

Size, caloric value and chemical composition were measured separately in the progeny of two northern pike (Esox lucius) females at 3-day intervals during the endogenous feeding period from hatching to final yolk resorption. Tissue, yolk and entire larvae were analysed separately in three groups of larvae that hatched at different times (between 88 and 106 degree-days post-fertilization). An integrated approach with the Gompertz model was used to compute the yolk conversion efficiency and time to maximum tissue size in early, mid and late hatched larvae. At hatching, unresorbed yolk of early hatched larvae contained more energy (39.20 J) and more protein (0.99 mg) compared to the yolk of larvae that hatched later (38.13 J and 0.92 mg protein for late hatched larvae, p < 0.05). In contrast, a significant reduction in tissue weight (-0.7 mg DW) and protein content (-0.5 mg) was found in early hatched larvae compared to those which hatched later (p < 0.05). Between days 9 and 12 post-hatching (108 and 144 degree-days post-hatching), close to the final yolk resorption, late hatched larvae stopped growing and their tissue began to be resorbed. This tissue resorption time was delayed in early hatched larvae which presented at the end of the experiment a greater tissue weight than late hatched ones. Yolk conversion efficiency in term of energy from hatching to complete yolk resorption stage was significantly higher for early and mid hatched larvae (51%) compared to late hatched ones (44%) (p = 0.004). Furthermore, the time to maximum tissue size was found to be negatively related to hatching time which implies that early hatched larvae take longer time to switch from one developmental stage to the next. The maximum tissue dry weight and energy content were found to be reached at approximately the same age post-fertilization for both early hatched and late hatched larvae, suggesting that the principal steps in a fish's lifespan are better correlated with time of fertilization than hatching time.

First insight into personality traits in Northern pike (Esox lucius) larvae: a basis for behavioural studies of early life stages

Personality traits have been studied for some decades in fish species. Yet, most often, studies focused on juveniles or adults. Thus, very few studies tried to demonstrate that traits could also be found in fish larvae. In this study, we aimed at identifying personality traits in Northern pike (Exos lucius) larvae. Twenty first-feeding larvae aged 21 days post hatch (16.1 +/− 0.4 mm in total length, mean +/− SD) were used to establish personality traits with two tests: a maze and a novel object. These tests are generally used for evaluating the activity and exploration of specimens as well as their activity and boldness, respectively. The same Northern pike twenty larvae were challenged in the two tests. Their performances were measured by their activity, their exploratory behaviour and the time spent in the different arms of the maze or near the novel object. Then, we used principal component analysis (PCA) and a hierarchical ascendant classification (HAC) for analysis of each data set separately. Finally, we used PCA reduction for the maze test data to analyse the relationship between a synthetic behavioural index (PCA1) and morphometric variables. Within each test, larvae could be divided in two sub groups, which exhibited different behavioural traits, qualified as bold (n = 7 for the maze test and n = 13 for the novel object test) or shy (n = 9 for the maze test and n = 11 for the novel object test). Nevertheless, in both tests, there was a continuum of boldness/shyness. Besides, some larvae were classified differently between the two tests but 40 % of the larvae showed cross context consistency and could be qualified as bold and/or proactive individuals. This study showed that it is possible to identify personality traits of very young fish larvae of a freshwater fish species.

Feeding of pike larvae (Esox lucius L.) in an alluvial river backwater: fatty acid as markers of two organic matter flows

Feeding of pike larvae (Esox lucius L.) in an alluvial river backwater: fatty acid as markers of two organic matter flows

Growth of pike larvae: effects of prey, turbidity and food quality

We studied experimentally the effects of turbidity and prey composition on pike larval growth and hypothesized that pike larval growth varies with turbidity and food quality. We reared the first-feeding pike larvae (Esox lucius) in laboratory tanks with (1) clear or (2) turbid water provided with zooplankton rations from (3) an inner and (4) an outer archipelago site. The sites differ in physical features, salinity, eutrophication status, zooplankton community structure and density. Pike larvae showed the highest weight increase in clear water with zooplankton from the outer site and the poorest weight increase in turbid water with zooplankton as prey from the inner site. Our fatty acid analysis revealed that unsaturated fatty acid levels were highest in the outer site. The relative percentage of copepods was also higher in the outer site. This study supports the hypothesis that turbidity weakens the ability of pike larvae to capture certain prey. Further, zooplankton community composition matters in turbid water, but is not a primary factor in clear water.

Hatching time effect on the intra-spawning larval morphology and growth in Northern pike (Esox luciusL.)

Based on the analysis of 11 morphometric variables of body (total length, body area and perimeter, myotome height and eye diameter) and yolk sac (length, height, area, perimeter and volume) of pike larvae, the aim of this study was to evaluate how larval size at hatching and growth of larvae hatched from single egg batches vary according to three hatching times: early, mid and late. Hatching time structures strongly pike larval morphometrics. Early hatched larvae have smaller body sizes at hatch, faster growth and higher yolk use efficiency than late hatched ones. Early hatched larvae seem to be premature and hatch at precocious developmental stage whereas late hatched individuals continue their growth within the egg shell and hatch at larger size but with lower reserves (yolk). A compensatory growth phase was observed for the early hatching pike larvae particularly during the first 5 days post hatch. Consequently, no significant difference in body parameters was recorded from day 10 post hatching whatever the hatching time. The higher growth accomplished by early hatched larvae may be related to a particular metabolic activity that converts more efficiently yolk into body tissues.

UV‐B Exposure Causes DNA Damage and Changes in Protein Expression in Northern Pike (Esox lucius) Posthatched Embryos

The ongoing anthropogenically caused ozone depletion and climate change has increased the amount of biologically harmful UV-B radiation, which is detrimental to fish in embryonal stages. The effects of UV-B radiation on the levels and locations of DNA damage manifested as cyclobutane pyrimidine dimers (CPDs), heat shock protein 70 (HSP70) and p53 protein in newly hatched embryos of pike were examined. Pike larvae were exposed in the laboratory to current and enhanced doses of UV-B radiation. UV-B exposure caused the formation of CPDs in a fluence rate-dependent manner, and the CPDs were found deeper in the tissues with increasing fluence rates. UV-B radiation induced HSP70 in epidermis, and caused plausible p53 activation in the brain and epidermis of some individuals. Also at a fluence rate occurring in nature, the DNA damage in the brain and eyes of pike and changes in protein expression were followed by severe behavioral disorders, suggesting that neural molecular changes were associated with functional consequences.

Does the zooplankton prey availability limit the larval habitats of pike in the Baltic Sea?

The objectives of this study were to (1) investigate whether the availability of suitable zooplankton prey limits the distribution of the coastal larval areas of pike ( Esox lucius) in two archipelago areas of the northern Baltic Sea and (2) compare the availability of zooplankton prey in spring between different types of coastal littoral habitat. According to the results, reed belt habitats formed by Phragmites australis constitute hot spots for zooplankton prey in the coastal ecosystem. During the spring, reed-covered shores of the inner archipelago maintained more than 10 times higher densities of copepods and cladocerans, the preferred prey for larval pike, compared to the other studied shores. Temperature conditions were also most favourable in the reed belt habitat. Thus, the reed belts of the inner and middle archipelago were shown to form the best habitat for larval pike in the coastal area of the northern Baltic Sea, and this was also the only habitat where pike larvae were found. Our results suggest that the poor survival and recruitment of pike in the outer archipelago, however, cannot exclusively be explained by sub-optimal feeding conditions of the larvae. There are also other important factors, presumably connected to the exposure to the open sea, that affect the distribution of the pike larvae. Our results, however, highlight the importance of sheltered coastal reed belt shores as reproduction habitat for spring-spawning fish in the northern Baltic Sea. Further, this study disproves the assumption that the seaweed bladder wrack ( Fucus vesiculosus) forms a reproduction habitat for pike in the coastal area.

Growth and feeding of juvenile pike Esox lucius (Esocidae) of different hatching dates during its first months of life

Groups of fingerlings of the pike Esox lucius, that hatched from the eggs of the same female at the beginning and end of hatching are compared. It was found that larvae of pike of the beginning of hatching passed to external feeding earlier. In the period of mixed and exogenous feeding, they not only grew, but also developed more rapidly than larvae from the same brood. It was shown that pike juveniles of the end of hatching were characterized by a retarded development and growth in the first weeks of life (until reaching a length of 100 mm and a weight of 7 g). In the second month of life, specimens of this group began to feed intensively, grow, and according to body length and weight, reached pike juveniles of the beginning of hatching. Pike fingerlings of the end of hatching were characterized by compensation growth that was manifested at the excess of fish food (at cultivation in separate aquariums when the inhibitory effect of large fish on the growth of small fish was excluded) and in ponds where fish food availability was considerably lower.

Foraging, growth and habitat choice in turbid water: an experimental study with fish larvae in the Baltic Sea

Eutrophication is a large problem in many marine and brackish-water areas. One of the consequences is algae-induced turbidity affecting visually feeding organisms, and behavioural changes of fish and other animals are common in turbid water. The aim of this study was to compare the performance of larval pike Esox lucius in turbid and clear water. We experimentally studied habi- tat choice, prey attacks and swimming activity of newly hatched larvae in the presence of a predator and competitors in relation to algae-induced turbidity. Our results demonstrated that the larvae spent less time in vegetation, performed more prey attacks and spent less time swimming in turbid water than in clear conditions. The presence of competitors increased the number of prey attacks, while the presence of a visual predator decreased the number of attacks. We also showed that pike larval weight was lower in high turbidity than in low turbidity. Our results show that algae-induced water turbidity affects both direct (i.e. feeding and habitat choice) and indirect qualities (i.e. weight) of pike larvae and may therefore affect larval survival and potentially even recruitment into the population.

Potential effects of spawning habitat changes on the segregation of northern pike (Esox lucius) and muskellunge (E. masquinongy) in the Upper St. Lawrence River

Changes in spawning habitat of northern pike (Esox lucius) may affect their segregation from and coexistence with the closely related muskellunge (E. masquinongy). We estimated the areal coverage of robust and shallow emergent vegetation in three shared-spawning bays in the Upper St. Lawrence River from aerial photographs taken from 1948 to 2003. Robust emergent vegetation (e.g., cattail) increased in coverage by 155–241% while shallow emergents (sedges) decreased by 46–96%. The loss of sedges, an important northern pike-spawning habitat, may facilitate greater spawning overlap in offshore-submersed aquatic vegetation within bay habitats used by muskellunge. Development rates and characteristics of northern pike and muskellunge eggs and larvae were compared to better understand the implications of greater spawning overlap. Northern pike eggs developed faster than muskellunge eggs at temperatures of 4.7–19°C, and adhesive eggs and the presence of adhesive papillae were present in both species. Equations were used to predict degree-day requirements for hatching and swim-up in three habitats (shallow emergents, bay, and offshore shoal) along a temperature gradient. Northern pike required more estimated degree days to reach hatching in bay and offshore shoal habitat relative to shallow emergent habitat due to cooler temperatures. Significant spawning overlap is known to occur within bay habitats, but poor success of northern pike in deep bay habitats and overall reductions in abundance are hypothesized to currently buffer muskellunge from potential negative interactions between these species.

Ecosystem Consequences of Cyanobacteria in the Northern Baltic Sea

Cyanobacteria of the Baltic Sea have multiple effects on organisms that influence the food chain dynamics on several trophic levels. Cyanobacteria contain several bioactive compounds, such as alkaloids, peptides, and lipopolysaccharides. A group of nonribosomally produced oligopeptides, namely microcystins and nodularin, are tumor promoters and cause oxidative stress in the affected cells. Zooplankton graze on cyanobacteria, and when ingested, the hepatotoxins (nodularin) decrease the egg production of, for example, copepods. However, the observed effects are very variable, because many crustaceans are tolerant to nodularin and because cyanobacteria may complement the diet of grazers in small amounts. Cyanobacterial toxins are transferred through the food web from one trophic level to another. The transfer rate is relatively low in the pelagic food web, but reduced feeding and growth rates of fish larvae have been observed. In the benthic food web, especially in blue mussels, nodularin concentrations are high, and benthic feeding juvenile flounders have been observed to disappear from bloom areas. In the littoral ecosystem, gammarids have shown increased mortality and weakening of reproductive success under cyanobacterial exposure. In contrast, mysid shrimps seem to be tolerant to cyanobacterial exposure. In fish larvae, detoxication of nodularin poses a metabolic cost that is reflected as decreased growth and condition, which may increase their susceptibility to predation. Cyanobacterial filaments and aggregates also interfere with both hydromechanical and visual feeding of planktivores. The feeding appendages of mysid shrimps may clog, and the filaments interfere with prey detection of pike larvae. On the other hand, a cyanobacterial bloom may provide a refuge for both zooplankton and small fish. As the decaying bloom also provides an ample source of organic carbon and nutrients for the organisms of the microbial loop, the zooplankton species capable of selective feeding may thrive in bloom conditions. Cyanobacteria also compete for nutrients with other primary producers and change the nitrogen (N): phosphorus (P) balance of their environment by their N-fixation. Further, the bioactive compounds of cyanobacteria directly influence other primary producers, favoring cyanobacteria, chlorophytes, dinoflagellates, and nanoflagellates and inhibiting cryptophytes. As the selective grazers also shift the grazing pressure on other species than cyanobacteria, changes in the structure and functioning of the Baltic Sea communities and ecosystems are likely to occur during the cyanobacterial bloom season.