Coping with flow: behavior, neurophysiology and modeling of the fish lateral line system

With the mechanosensory lateral line fish perceive water motions relative to their body surface and local pressure gradients. The lateral line plays an important role in many fish behaviors including the detection and localization of dipole sources and the tracking of prey fish. The sensory units of the lateral line are the neuromasts which are distributed across the surface of the animal. Water motions are received and transduced into neuronal signals by the neuromasts. These signals are conveyed by afferent nerve fibers to the fish brain and processed by lateral line neurons in parts of the brainstem, cerebellum, midbrain, and forebrain. In the cerebellum, midbrain, and forebrain, lateral line information is integrated with sensory information from other modalities. The present review introduces the peripheral morphology of the lateral line, and describes our understanding of lateral line physiology and behavior. It focuses on recent studies that have investigated: how fish behave in unsteady flow; what kind of sensory information is provided by flow; and how fish use and process this information. Finally, it reports new theoretical and biomimetic approaches to understand lateral line function.     

The invasion of an alien characiform fish and the decline of a native congener in a Neotropical river-floodplain system

Hydrobiologia - Using a long time series, we analyzed trends in abundance of two characiform fishes in the upper Paraná River and its floodplain: the native Schizodon altoparanae and its alien...     

Synergistic interactions within disturbed habitats between temperature, relative humidity and UVB radiation on egg survival in a diadromous fish

Anthropogenic impacts, including urbanization, deforestation, farming, and livestock grazing have altered riparian margins worldwide. One effect of changes to riparian vegetation is that the ground-level light, temperature, and humidity environment has also been altered. Galaxias maculatus, one of the most widely distributed fishes of the southern hemisphere, lays eggs almost exclusively beneath riparian vegetation in tidally influenced reaches of rivers. We hypothesized that the survival of these eggs is greatly affected by the micro-environment afforded by vegetation, particularly relating to temperature, humidity and UVB radiation. We experimentally reduced riparian vegetation height and altered shading characteristics, tracked egg survival, and used small ground-level temperature, humidity and UVB sensors to relate survival to ground-level effects around egg masses. The ground-level physical environment was markedly different from the surrounding ambient conditions. Tall dense riparian vegetation modified ambient conditions to produce a buffered temperature regime with constant high relative humidity, generally above 90%, and negligible UVB radiation at ground-level. Where vegetation height was reduced, frequent high temperatures, low humidity, and high UVB irradiances reduced egg survival by up to 95%. Temperature effects on egg survival were probably indirect, through reduced humidity, because developing eggs are known to survive in a wide range of temperatures. In this study, it was remarkable how such small variations in relatively small sites could have such a large effect on egg survival. It appears that modifications to riparian vegetation and the associated changes in the physical conditions of egg laying sites are major mechanisms affecting egg survival. The impacts associated with vegetational changes through human-induced disturbances are complex yet potentially devastating. These effects are particularly important because they affect a very small portion of habitat that is required to complete the life history of a species, despite the wide distribution of adults and juveniles across aquatic and marine environments.     

Effects of a retaining wall and an artificial embankment on nearshore littoral habitats and biota in a large Alpine lake

Hydrobiologia - The littoral zones of many Central European lakes are severely altered by lake-side retaining walls. These are suspected to impair littoral biota due to the reflection of incoming...     

Mathematical description of the stimuli to the lateral line system of fish derived from a three-dimensional flow field analysis

The three-dimensional potential flow field around a moving fish with an axially symmetric body is investigated mathematically. The case of a moving fish in open water and that of one approaching a plane surface in front of it are considered. For these cases the spatial and temporal distributions of the stimuli to the lateral line system are derived from the flow field analysis. This is done in dependence on the shape and the size of the fish.     

Complexity of bacterial communities in a river-floodplain system (Danube, Austria)

Natural floodplains play an essential role in the processing and decomposition of organic matter and in the self-purification ability of rivers, largely due to the activity of bacteria. Knowledge about the composition of bacterial communities and its impact on organic-matter cycling is crucial for the understanding of ecological processes in river-floodplain systems. Particle-associated and free-living bacterial assemblages from the Danube River and various floodplain pools with different hydrological characteristics were investigated using terminal restriction fragment length polymorphism analysis. The particle-associated bacterial community exhibited a higher number of operational taxonomic units (OTUs) and was more heterogeneous in time and space than the free-living community. The temporal dynamics of the community structure were generally higher in isolated floodplain pools. The community structures of the river and the various floodplain pools, as well as those of the particle-associated and free-living bacteria, differed significantly. The compositional dynamics of the planktonic bacterial communities were related to changes in the algal biomass, temperature, and concentrations of organic and inorganic nutrients. The OTU richness of the free-living community was correlated with the concentration and origin of organic matter and the concentration of inorganic nutrients, while no correlation with the OTU richness of the particle-associated assemblage was found. Our results demonstrate the importance of the river-floodplain interactions and the influence of damming and regulation on the bacterial-community composition.     

Vertical, lateral and diurnal drift patterns of fish larvae in a large lowland river, the Elbe

A ringnet was used to sample drifting fish quantitatively at distinct depth strata. This method was chosen to examine the lateral, vertical and diurnal drift patterns of fish fry during four sampling campaigns in May 1998 and 1999 in the middle Elbe River, close to the city of Schnackenburg (stream kilometre 475). It became apparent that the fish larvae concentrated mainly at the surface of the right side of the main channel. Fourteen fish species of the four taxonomic families Percidae, Cyprinidae, Osmeridae and Gadidae were caught. Percid fishes (pike‐perch and perch) dominated the caught fish fry assemblage. Several environmental parameters were included in a direct gradient analysis in order to detect influencing variables. The main significant qualities were a temporal aspect and the shore distance. Other important influencing variables were suspended particular matter (SPM), fishing depth, time of the day, current velocity and the filtered volume. Negative correlations of abundance and shore distances and concentrations of SPM were found for several species as well as for the total abundance.     

Distribution and abundance of fish in deep-sea coral habitats

Experimental fishing with long-lines and gillnets was conducted on the continental shelf off southwestern Norway between 150 and 350 m depth. Abundance and distribution of redfish (Sebastes marinus L., 1758), ling (Molva molva L., 1758), and tusk (Brosme brosme Ascanius, 1772) were quantified in Lophelia pertusa (L., 1758) coral reefs and in non-coral habitats. The largest catches of redfish were made with long-line fleets set in coral reef habitats. Ling and tusk were also most numerous in coral habitats, although not statistically significant. Fish caught in coral habitats tended to be larger in size than in non-coral habitats. The diet of redfish, tusk and ling included the same prey groups in all habitats, but they differed at the species level. Lophelia-reefs may provide a profitable feeding place for tusk. For the planktivorous Sebastes, on the other hand, their affinity to the reefs seems primarily to be related to the physical structure offered by the reefs.     

Effects of environmental stressors and their interactions on zooplankton biomass and abundance in a large eutrophic lake

We assessed long-term impacts of multiple stressors and their interaction on the zooplankton community of the large, eutrophic, cyanobacteria-dominated Lake Peipsi (Estonia, Russia). Stressor dataset consisted in time series (1997–2018) of temperature, nutrients, pH, water transparency, phytoplankton biomass and taxonomic richness. The best predictors were selected with random forests machine-learning algorithms and the subsequent models were constructed with generalized linear modeling. We also aimed to identify graphical thresholds representing non-linear, marked responses of abundance or biomass to stressors. Temperature was the dominant stressor for explaining zooplankton abundance and biomass, followed by cyanobacteria biomass, total nitrogen concentration and water transparency. The effect of water temperature was positive, whereas the effect of cyanobacteria became negative after their biomass exceeded a threshold of?~?2 mg l^?1. However, the two stressors together had antagonistic effects on zooplankton, causing a decrease in biomass and abundance. For zooplankton, critical thresholds of total nitrogen (~?700 μg l^?1), total phosphorus (~?70 μg l^?1), and water transparency (~?1.4 m) after which zooplankton metrics changed drastically, were determined. These findings show that although lake warming alone could be positive for zooplankton, the necessity of reducing interacting stressors that influence harmful cyanobacteria growth and biomass, especially nitrogen loads, must be considered.

     

Informative and misinformative interactions in a school of fish

Quantifying distributed information processing is crucial to understanding collective motion in animal groups. Recent studies have begun to apply rigorous methods based on information theory to quantify such distributed computation. Following this perspective, we use transfer entropy to quantify dynamic information flows locally in space and time across a school of fish during directional changes around a circular tank, i.e., U-turns. This analysis reveals peaks in information flows during collective U-turns and identifies two different flows: an informative flow (positive transfer entropy) from fish that have already turned to fish that are turning, and a misinformative flow (negative transfer entropy) from fish that have not turned yet to fish that are turning. We also reveal that the information flows are related to relative position and alignment between fish and identify spatial patterns of information and misinformation cascades. This study offers several methodological contributions and we expect further application of these methodologies to reveal intricacies of self-organisation in other animal groups and active matter in general.     

Prevalence of kairomone-induced diapause in Daphnia magna from habitats with and without fish

The prevalence of the diapause response of the freshwater crustacean Daphnia magna to chemical cues on fish predation was evaluated in 35 clones originating from 14 European water bodies—inhabited or not inhabited by fish. Clonal lineages of experimental animals were cultured for 4 weeks in the presence or absence of water to which an extract of faeces of crucian carps (Carassius carassius), that were fed with Daphnia, was added. The proportion of females producing diapausing forms during the experimental period was used as a measure of the diapause response. A positive diapause response to fish predation cues was observed in 43% of investigated clones that originated from 71% of the water bodies tested. This indicated that the diapause response to fish scent is a common phenomenon in Daphnia magna from various locations in Europe. Surprisingly, no signs of a stronger diapause reaction to the tested cues were found in Daphnia originating from water bodies inhabited by fish compared with those from fish-free habitats.     

Effects of three Caribbean cleaner shrimps on ectoparasitic monogeneans in a semi-natural environment

Most research on cleaning symbioses on coral reefs has focused on fish clients being cleaned by smaller fishes. While many shrimps and other crustaceans are reported as cleaners, whether they remove parasites from fish hosts and can effectively regulate populations of ectoparasites is unclear. The effects of Pederson shrimp (Periclimenes pedersoni), spotted shrimp (P. yucatanicus), and banded coral shrimp (Stenopus hispidus), on the parasitic monogenean Neobenedenia melleni on a host reef fish, blue tang (Acanthurus coeruleus), were investigated. The abundance and size of N. melleni from fish with and without access to shrimps in a semi-natural macrocosm was quantified. P. pedersoni had a strong effect on both the abundance and size of parasites. In contrast, P. yucatanicus and S. hispidus had no effect on the abundance of parasites but had a small yet statistically significant effect on average size. These data suggest that P. pedersoni can play a significant role in the biological regulation of at least some ectoparasites on Caribbean reef fishes, but further suggest that some other shrimps regarded as “cleaners” may have little or no effectiveness at removing parasites and underscore the need for further verification before this term is applied.     

Effects of extreme low flows on freshwater shrimps in a perennial tropical stream

• 1 Long-term data on rainfall suggests that perennial rainforest streams rarely are subject to drying of riffles or pools in the wet, non-seasonal Caribbean climate of Puerto Rico. Unusually low rainfall in 1994 caused some headwater riffles to dry out completely, resulting in isolated pools, reduced pool volumes and loss of access to microhabitats by benthic invertebrates.
• 2 From 1992 to 1998, shrimp populations were sampled bimonthly using baited traps in six pools along 1200 m (from 305 to 480 m in altitude) of Quebrada Prieta, a second-order headwater stream in the Luquillo Experimental Forest (Caribbean National Forest).
• 3 Following contraction of the smaller and shallower pools in the most upstream section of the stream, mean densities of the dominant shrimp (Atya lanipes) increased from 22 to 75 shrimp m⁻² of pool area during the 1994 drought year. A second common species (Xiphocaris elongata) increased from 5 to 14 shrimp m⁻². A smaller percentage of adults of both species was gravid during the drought.
• 4 Following the 1994 drought (1995–1998), densities of both shrimp species and reproductive activity of Atya returned to predrought (1990–1993) levels. However, the reproductive activity of Xiphocaris remained lower than in the predrought period.
• 5 It is suggested that prolonged droughts, even in tropical rainforest biomes, may significantly alter aquatic communities through localised crowding effects resulting from habitat contraction, and lead to prolonged decreases in reproductive output. Consequently, major alterations in aquatic populations and communities would be predicted by current climate change scenarios of decreased total rainfall and increased variability.

     

Effects of habitat complexity on trophic interactions of three congeneric fish species

Aquatic Ecology - Habitat complexity can substantially alter trophic relationships, such as competitive and predatory interactions, between fish species. This study aimed to evaluate how trophic...     

Locomotion and flow speed preferences in natural habitats by large water striders,Ptilomera tigrina,with micro-morphological adaptations for rowing

Journal of Ethology - Water strider (Gerridae) morphology and behavior have become the focus of interdisciplinary research in biological diversification and bio-inspired technology. However, the...     

Patterns of spacing in a coral reef fish in two habitats on the Great Barrier Reef

Patterns of spacing in the butterflyfish Chaetodon trifasciatus (Pisces, Chaetodontidae) were studied in two habitats on the southern Great Barrier Reef. Pairs of fish were found to defend territories at reef slope and lagoon study sites. Territories were 2·7–3·7 times larger in the lagoon than on the reef slope, where population density and food abundance were greater. No significant changes occurred in the sizes of territories in either habitat over on year, but patterns of spacing were generally more variable in the lagoon habitat. This was interpreted as a response to low population density and poor habitat quality.     

Sequence analysis of a fish vitellogenin cDNA with a large phosvitin domain

Vitellogenins (Vtg) are egg-yolk precursor proteins crucial for reproductive success in oviparous animals. We have cloned the first complete cichlid Vtg cDNA from the tilapia fish, Oreochromis aureus. This cDNA has the largest phosvitin (PV) domain amongst piscine Vtgs, being comparable to those of lamprey, Xenopus, and chicken. Thus, the size of PV is independent of the evolutionary advancement of a species. The closer interspecific relationship between O. aureus Vtg1 and Fundulus VtgII than the intraspecific relationship between Fundulus VtgI and II isoforms suggests that teleost ancestors had at least two Vtg isoforms. Contrary to the results of previous phylogenetic inference using Vtgs which indicate that insect lineage is most diverged and nematodes are closer to vertebrate lineage, our results show that nematodes and hexapods form two monophyletic sister groups. Another arthropod taxon, represented by a malacostracan crustacean, Penaeus japonicus, appears to be more closely related to the vertebrates than the hexapods.