Performance of Larval Walleye Cultured Intensively in Clear and Turbid Water1

The purposes of this study were to verify the findings of a previous study that showed improved performance of walleyes Stizostedion vitreum raised in turbid water (16.1–49.7 nephelometric turbidity units, NTU), to determine the minimum level of turbidity that would reduce or eliminate the tendency of fry to cling to tank sidewalls, and to evaluate a dye (Aquashade) as a substitute for increasing turbidity with clay. Fish were reared from 2 to 21 d posthatch in clear water (0.3 NTU), turbid water (23.8 NTU), and water colored blue with Aquashade at 1.8 and 17.4 mg/L. Fish in turbid water began consuming feed earlier than those in clear water or in either of the dye solutions. At the termination of the experiment, survival, gas bladder inflation, length, and weight were significantly greater for fry reared in the turbid water than in the other three treatments. In turbid water, survival was 35.1 %, with 99.3% gas bladder inflation. The mean weight of fry reared in turbid water was 270–380% greater...

The influence of turbidity on larval walleye, Stizostedion vitreum, behavior and development in tank culture

Submerged macrophytes growing in clear- and turbid water may develop morphological differences as adaptations to difference light levels. Plant forms altered over generations and longtime are regarded as ecotypes and the changes are assumed to be persistent, even if the plants are returned to their ancestral environment. Specimens of Potamogeton malaianus from clear and turbid water zones of Lake Taihu were compared in their native settings and after transplanting to similar and different environments. Results showed that turbid water forms of P. malaianus had significantly larger shoots with more and longer leaves and more biomass concentrated near the water surface. After transplanting into clear water, the daughter shoots arising from clear or turbid water plants showed no significant differences from their mother shoots, but showed significant differences from each other. After transplanting into turbid water, mother and daughter shoots originating from turbid water plants had similar morphologies, but were significantly different from clear water plants. Plants transplanted from clear water did not survive in turbid water. Our results suggest that P. malaianus forms special ecotype in turbid water, which may help plants maximize their sunlight-harvesting potential and thus might contribute to an observed expansion of the species into turbid water areas of eutrophic lakes.

Water turbidity affects the establishment of Neochetina eichhorniae (Warner) (Coleoptera: Curculionidae): Implications for biological control of water hyacinth

Thorn fish Terapon jarbua (Forskål) predation on juvenile white shrimp Penaeus indicus H. Milne Edwards and brown shrimp Metapenaeus monoceros (Fabricius): the effect of turbidity, prey density, substrate type and pneumatophore density

Warming and eutrophication negatively affect freshwater ecosystems by modifying trophic interactions and increasing water turbidity. We need to consider their joint effects on predator-prey interactions and how these depend on the thermal evolution of both predator and prey. We quantified how 4°C warming and algae-induced turbidity (that integrates turbidity per se and increased food for zooplankton prey) affect functional response parameters and prey population parameters in a common-garden experiment. We did so for all combinations of high- and low-latitude predator (damselfly larvae) and prey (water fleas) populations to assess the potential impact of thermal evolution of predators and/or prey at a high latitude under warming using a space-for-time substitution. We then modelled effects on the system stability (i.e. tendency to oscillate) under different warming, turbidity and evolutionary scenarios. Warming and turbidity had little effect on the functional response parameters of high-latitude predators. In contrast, warming and turbidity reduced the handling times of low-latitude predators. Moreover, warming increased the search rates of low-latitude predators in clear water but instead decreased these in turbid water. Warming increased stability (i.e. prevented oscillations) in turbid water (except for the 'high-latitude predator and high-latitude prey' system), mainly by decreasing the prey's carrying capacity and partly also by decreasing search rates, while it did not affect stability in clear water. Algae-induced turbidity generally decreased stability, mainly by increasing the prey's carrying capacity and partly also by increasing search rates. This resembles findings that nutrient enrichment can reduce the stability of trophic systems. The expected stability of the high-latitude trophic system under warming was dependent on the turbidity level: our results suggest that thermal plasticity tends to destabilize the high-latitude trophic system under warming in clear water but not in turbid water, and that thermal evolution of the predator will stabilize the high-latitude system under warming in turbid water but less so in clear water. The extent to which thermal plasticity and evolution shape trophic system stability under warming may strongly differ between clear and turbid water bodies, with their contributions having a more stabilizing role in turbid water.

Laboratory experiments were performed in clear and turbid water to determine the effects of prey size, orientation, and movement on the reactive distance of largemouth bass (Micropterus salmoides) when feeding on crayfish (Procambarus acutus). In clear water, the reactive distance increased linearly with an increase in prey size, and prey movement resulted in a significant increase in the reactive distance. Prey orientation (head-on versus perpendicular) did not change the reactive distances. In moderately turbid water, the reactive distance did not increase with increased prey size, and prey movement did not result in any changes in the reactive distance. The absence of any effects of prey orientation in clear water or prey movement in turbid water is inconsistent with results from studies using different species (primarily planktivorous fish). I propose that largemouth bass change their foraging tactics as prey visibility changes. When prey are highly visible (low turbidity), predators attack (react) only after prey recognition, which is based on multiple cues such as prey size (length, width) and movement. When prey are less visible (high turbidity), predators attack immediately upon initial prey sighting, which does not depend on prey size or movement.

It has been demonstrated that a surface spray is needed to obtain a high percentage of gas bladder inflation (GBI) in intensively cultured larval walleyes Sander vitreus fed dry diets and that turbid‐water culture substantially enhances larval survival and growth. It was not previously known whether a surface spray is needed to obtain GBI when larvae are cultured in turbid water, which is produced by intermittently adding clay slurry to the culture tank. The present study was undertaken to test whether turbid water alone would enhance GBI without need for a surface spray. Larval walleyes were cultured with formulated feed from 2 to 28 d posthatch (dph) in tanks containing turbid water (∼55 nephelometric turbidity units) with surface spray (WS tanks) or without surface spray (WOS tanks). Larvae were stocked at a density of 20 fish/L and were given formulated feed every 5 min for 22 h/d. All husbandry and water quality conditions were similar between experimental treatments. Gas bladder inflation was 100% in fish surviving to 28 dph in WS tanks, but GBI was only 3.3% in WOS tanks. Fry survival (50% WS; 34% WOS), final length, and final weight were not significantly different between treatments. The results conclusively show that surface spray is essential for GBI in walleyes.

A physical analysis of diurnal temperature regimes in clear and turbid water layers: A problem in rice culture

Native freshwater fish populations are among the world's most threatened taxa due to the combined effects of habitat degradation and invasive alien species. Habitat degradation negatively impacts native species, whereas invasive species tend to possess adaptations, such as thermal and salinity tolerance, that are more suited to the degraded environment. Sensory ecology may also be a contributing factor. Most threatened native species are visual feeders, whereas invasive species found in degraded systems often have nonvisual specializations. Behavioral and distributional characteristics of the invasive Western Mosquitofish Gambusia affinis and the New Zealand native Inanga Galaxias maculatus illustrate the potential for sensory biology to influence foraging success, distribution, and species interaction between degraded and clear habitats. Behavioral trials measured the change in feeding rate in clear (0 NTU) and turbid (100 NTU) water over 30 min for Inanga and Western Mosquitofish feeding on brine shrimp Artemia salina nauplii. These experiments showed that Western Mosquitofish maintained similar feeding rates between clear and turbid water, whereas the native species exhibited a marked decline in feeding efficiency in turbid water. Across a strong natural turbidity boundary, the alien species was found to dominate turbid habitat less than 1 m from clear water, where both species were found. Accounting for sensory biology as a potential contributing factor in the establishment of invasive fish species in degraded habitat may help to identify invasive species risk and to shape strategies for rehabilitating native species.

Increasing turbidity in streams and rivers near human activity is cause for environmental concern, as the ability of aquatic organisms to use visual information declines. To investigate how some organisms might be able to developmentally compensate for increasing turbidity, we reared guppies (Poecilia reticulata) in either clear or turbid water. We assessed the effects of developmental treatments on adult behavior and aspects of the visual system by testing fish from both developmental treatments in turbid and clear water. We found a strong interactive effect of rearing and assay conditions: fish reared in clear water tended to decrease activity in turbid water, whereas fish reared in turbid water tended to increase activity in turbid water. Guppies from all treatments decreased activity when exposed to a predator. To measure plasticity in the visual system, we quantified treatment differences in opsin gene expression of individuals. We detected a shift from mid-wave-sensitive opsins to long wave-sensitive opsins for guppies reared in turbid water. Since long-wavelength sensitivity is important in motion detection, this shift likely allows guppies to salvage motion-detecting abilities when visual information is obscured in turbid water. Our results demonstrate the importance of developmental plasticity in responses of organisms to rapidly changing environments.

We tested how algal turbidity and light conditions influence anti-predator behaviour of first-feeding pike. Results showed that pike larvae were able to detect the predator by both chemical and visual signals in turbid water. However, the anti-predator behaviour was reduced in turbid water compared with clear water. Larvae hid in the vegetation in the presence of predator cues more in clear water than in turbid water. The attack rate on zooplankton in clear water was lower in the presence of predator cues, whereas no such difference was detected in turbid water. Both of these results indicate that turbidity acted as a refuge for larvae. Light proved to be an important regulating factor for feeding pike in the absence of predators, demonstrated as lowered attack rates in 50 light level in both clear and turbid water. This indicates that long-term turbidity may be critical for small larvae, which need to feed continuously to survive.

High turbidity and elevated water temperature are environmental stressors that can co-occur in freshwater ecosystems such as when deforestation increases solar radiation and sedimentary runoff. However, we have limited knowledge about their combined impacts on fish behaviour and physiology. We explored independent and interactive effects of sedimentary turbidity and temperature on the swimming activity and both thermal and hypoxia tolerance of the Pugnose Shiner (Miniellus anogenus, formerly Notropis anogenus), a small leuciscid fish listed as Threatened under Canada's Species at Risk Act (SARA). Fish underwent a 15-week acclimation to two temperatures (16°C or 25°C) crossed with two turbidities (~0 NTU or 8.5 NTU). Swimming activity was measured during the first 8weeks of acclimation. Fish in warm water were more active compared to those in cold water, but turbidity had no effect on activity. Behavioural response to hypoxia was measured after 12weeks of acclimation, as the oxygen level at which fish used aquatic surface respiration (ASR). Fish in warm water engaged in ASR behaviour at higher oxygen thresholds, indicating less tolerance to hypoxia. Turbidity had no effect on ASR thresholds. Finally, thermal tolerance was measured as the critical thermal maximum (CTmax) after 13-15weeks of acclimation. Acclimation to warm water increased fish CTmax and Tag (agitation temperature) but reduced the agitation window (°C difference between Tag and CTmax) and thermal safety margin (°C difference between the acclimation temperature and CTmax). Furthermore, fish in warm, turbid water had a lower CTmax and smaller thermal safety margin than fish in warm, clear water, indicating an interaction between turbidity and temperature. This reduced thermal tolerance observed in Pugnose Shiner in warm, turbid water highlights the importance of quantifying independent and interactive effects of multiple stressors when evaluating habitat suitability and conservation strategies for imperilled species.

Certain terrestrial animals use sky polarization for navigation. Certain aquatic species have also been shown to orient according to a polarization stimulus, but the correlation between underwater polarization and Sun position and hence the ability to use underwater polarization as a compass for navigation is still under debate. To examine this issue, we use theoretical equations for per cent polarization and electric vector (e-vector) orientation that account for the position of the Sun, refraction at the air-water interface and Rayleigh single scattering. The polarization patterns predicted by these theoretical equations are compared with measurements conducted in clear and semi-turbid coastal sea waters at 2 m and 5 m depth over sea floors of 6 m and 28 m depth. We find that the per cent polarization is correlated with the Sun's elevation only in clear waters. We furthermore find that the maximum value of the e-vector orientation angle equals the angle of refraction only in clear waters, in the horizontal viewing direction, over the deeper sea floor. We conclude that navigation by use of underwater polarization is possible under restricted conditions, i.e. in clear waters, primarily near the horizontal viewing direction, and in locations where the sea floor has limited effects on the light's polarization.

Detectability of emergency lights for underwater escape : Allan, J.R., Brennan, D.H., and Richardson, G.Aviation, Space and Environ Med, 1989, 60.3, 199–204, 11 refs