Is the use of turmeric in the diet safe for fish?

With this study, we aimed to assess the safety of using Curcuma longa in fish feed. Juvenile Astyanax aff. bimaculatus (0.83 ± 0.04 g) were kept in 24 80‐L aquaria, at a density of 0.5 fish L^?1 for 60 days. Six diets supplemented with 0.0, 20.0, 40.0, 60.0, 80.0 and 100.0 g kg^?1 were evaluated. Histopathological analysis of the gills showed that there was an increasing linear effect of turmeric on the frequency of lamellar aneurysm, hypertrophy of mucous cells, oedema and necrosis. There was a quadratic effect of turmeric supplementation on the frequency of fusion and disruption of secondary lamellae, vacuolation and hypertrophy of the epithelial cells, and the estimated values to minimize these variables were 4.63, 25.93 and 24.46 g kg^?1 respectively. There was a quadratic effect of turmeric on the gills index (I_BRA), and the estimated value to minimize this index was 30.23 g kg^?1. No effect of turmeric on the frequency of histopathological changes and organ index in fish liver was observed. Thus, we conclude that turmeric is not hepatotoxic for A. aff. bimaculatus; however, its use is safe at concentrations up to 30.23 g kg^?1 diet as a function of its gill toxic effect at higher doses.     

Stressing fish in Recirculating Aquaculture Systems (RAS): does stress induced in one group of fish affect the feeding motivation of other fish sharing the same RAS?

As a consequence of water re‐use and high stocking densities, Recirculating Aquaculture Systems (RAS) may lead to an accumulation of substances released by the fish into the water, e.g. cortisol and alarm pheromones. This study investigated the effect of stressing fish on the feeding motivation of other fish not subjected to stress but sharing the same water of stressed fish. Two identical RAS were used (operated at 30 L kg feed^?1 day^?1) and contained grouped (stressed fish) and individually (receiving water from stressed fish) housed Nile tilapia. A stress test was applied in grouped housed fish on days 17 and 55. Feeding behaviour (intake and latency) was recorded in the individually housed fish 3 days before, during and 3 days after the stress test. The results showed no effect on feeding behaviour in fish receiving the water from stressed fish. These results could be a consequence of insufficient cortisol/alarm cues' release by the stressed fish into the water or inactivity of such substances, either due to a trapping effect of humic acids or due to degradation in the nitrification and denitrification processes. Future research is needed to clarify how these processes may affect the water concentration of cortisol and alarm pheromones and should be extended by measuring other behavioural and physiological traits.     

Can timing of spawning explain the increase in egg size with female size in salmonid fish?

A common observation is that egg size increases with maternal size within populations. Several hypotheses have been proposed to explain this phenomenon. Most recently, it was suggested that the optimal egg size depends on female size due to correlations between (i) breeding time and egg size selection and (ii) female size and breeding time, and as such, the positive egg size–maternal size relationship represents an adaptive strategy. Here, we test the second of these two premises in two salmonid species, Atlantic salmon (Salmo salar) and coho salmon (Oncorhynchus kisutch) for which we have detailed breeding and egg size data. The body size of spawning females decreased throughout the season in coho salmon, but not in Atlantic salmon. Furthermore, we did not find a direct correlation between egg size and breeding time, which would also be expected if this premise was correct. Accordingly, breeding date does not appear to be as important as other factors in shaping among female differences in egg size.     

When in life does density dependence occur in fish populations?

Fisheries advice is based on demographic calculations, which assume that density‐dependent processes regulating recruitment occur only in early life. This assumption is challenged by laboratory and lake studies and some recent indications from marine systems that demonstrate density‐dependent regulation late in life. By accounting for spatial dynamics of a population, something that has previously been ignored in models of fish, we show that density‐dependent regulation is determined by the size of the habitat: in small habitats, for example small lakes, regulation occurs late in life, while it can occur early in large habitats. When regulation happens late in life, fisheries yield is maximized by exploitation of mainly juvenile fish, while exploiting mature fish maximizes yield if regulation happens early. We review and interpret observations of density dependence in the light of the theory. Our results challenge the current assumption that density dependence always occurs early in life and highlights the need for an increased understanding of density‐dependent processes. This can only come about by a change of focus from determining stock‐recruitment relationships towards understanding when and how density‐dependent regulation occurs in nature.     

Do fish isotopic niches change in an Amazon floodplain lake over the hydrological regime?

Floodplain lakes are ecosystems characterised by annual flood and dry cycles. Fish ecology is influenced by the flood pulse due to the large influx of allochthonous food resources and diversification of habitats during the flood cycle, while during the dry cycle, fishes tend to be confined in reduced habitat. The aim of this study was to evaluate the seasonal variation in trophic niche width and overlap of four species—Mylossoma duriventre, Prochilodus nigricans, Cichla.pleiozona and Serrasalmus rhombeus—in an Amazonian floodplain lake. Stable isotope analyses were used to estimate trophic niche width and overlap during the flood and dry seasons. We hypothesised broader niche width for all species during the flood cycle and a higher degree of overlap between the two piscivorous fishes during the dry cycle. Isotopic niche width was 72% broader for P. nigricans, 61% for S. rhombeus and 54% for C. pleiozona during the dry cycle, which did not support our hypothesis. Core niche width overlaps were not observed between piscivorous species in either flood or dry cycle. The results indicate that seasonal variation in isotopic niche width is specific to feeding habit. Understanding how fish trophic ecology responds to changes in the hydrological regime during the seasons is crucial for sustainable fishery management in a region where many people rely heavily on fish for nutritional and economic purposes.     

How much do fish aggregating devices (FADs) modify the floating object environment in the ocean?

Natural floating objects (e.g., logs) have always been a component of the habitat of tropical tunas. However, the introduction of fish aggregating devices (FADs) modifies this environment. To assess the changes due to the deployment of FADs, we compared the spatial distribution of natural and artificial floating objects (FADs), using data from observers onboard tuna purse seine vessels in the Indian Ocean from December 2006 to December 2008. Although natural objects occur more commonly in waters south of 7°S and FADs are more common in waters north of 7°S, all types of floating objects can be found everywhere. Using different spatial scales (quadrats of size 1° × 1°, 2° × 2°, 5° × 5°, and 10° × 10°), we computed the proportion of FADs observed in quadrats without natural objects. The scale of 2° × 2° quadrats represented a threshold: distributions of the two types of objects were different at scales smaller than this threshold. The strongest change that has occurred since the introduction of FADs (besides the increased catches) has been the dramatic increase in the total number of floating objects. Since the introduction of FADs, the number of objects has at least doubled everywhere (except in the Mozambique Channel and Chagos) and in some areas (e.g., Somalia area) the multiplication factor has reached as high as 20 or 40. Our study sets the ranges of values of key parameters of the floating object environment, which are crucial in the design of future experimental studies aimed at investigating the impacts of FADs on the ecology of tunas.     

To sea or not to sea? Multiple lines of evidence reveal the contribution of non‐diadromous recruitment for supporting endemic fish populations within New Zealand's longest river

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Fish navigation in the vertical dimension: can fish use hydrostatic pressure to determine depth?

Fish live in complex volumetric habitats, and as such, face a challenging environment through which to navigate. This problem might be simplified if fish could monitor their depth and determine their position within the water column. One possible cue that they could use to ascertain their vertical position is hydrostatic pressure, which varies linearly with depth. Until recently it was assumed that fish were incapable of using hydrostatic pressure to measure depth as they do not possess a mechanism to sense absolute pressure. However, in a recent article by G. Taylor et al., we describe a novel mechanism whereby fish could determine their depth by using the rate in change of pressure mediated by changes in swim‐bladder volume, together with their vertical speed. This mechanism requires fish to be able to sense changes in pressure using their swim‐bladder. Here, we examine fish sensitivity towards hydrostatic pressure by reviewing the literature from behavioural and physiological experiments. This research suggests that fish are acutely sensitive to the magnitude and sign of hydrostatic pressure changes, via changes in the volume of the swim‐bladder. We argue that fish have the necessary physiological measurements to sense the rate in change of pressure, meaning they are able to use the mechanism proposed by Taylor et al. to determine their vertical location. This has profound implications for the study of navigation through volumes, by providing a reliable global cue that fish can use to determine their depth.     

Does the presence of microalgae influence fish larvae prey capture?

The green water technique has been widely shown to improve fish larvae growth, survival and feed ingestion. Therefore, fish larvae (Sparus aurata L. and Solea senegalensis Kaup) feeding behaviour was studied through gut content analysis, when using different species of microalgae, as the ‘green water’ technique. Six treatments were used: Stain – food green stain; Tetra – microalgae Tetraselmis chuii; Iso – microalgae Isochrysis galbana; Tetra Sup –T. chuii supernatant (obtained from centrifugation); Phyto – a microalgae paste, Nannochloropsis oculata, (Phytobloom^®); and C water – clear water, as control. At 9, 16 and 23 days after hatching (DAH) for S. aurata, and 4, 9 and 14 DAH for S. senegalensis, 40 unfed fish larvae were transferred to 3 L experimental tanks, filled with the different ‘green water’ technique. Fish larvae were sampled 2 h after being fed with live prey, anaesthetized and fixed in buffered formaldehyde for posterior gut content determination. Feeding was evaluated by the feeding rate, percentage of larvae with prey items in the digestive tract and feeding intensity, number of prey in each larva digestive tract. Fish larvae feeding ability was influenced by the interaction between light conditions and substances provided by the presence of microalgae during fish larvae development. Sparus aurata was more dependent on microalgae addition than S. senegalensis larvae, which may be related to the type of prey, larval behaviour, ontogeny and physiology. The presence of microalgae influenced the selection of larger prey (Artemia over rotifers) by S. aurata aged 23 DAH.     

Can satellite ponds buffer the impact of introduced fish on newts in a mountain pond network?

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Do wild fish species contribute to the transmission of koi herpesvirus to carp in hatchery ponds?

The koi herpesvirus (KHV) has spread worldwide since its discovery in 1998 and causes disease and mortality in koi and common carp populations with a high impact on the carp production industry. Many investigations have been conducted to examine ways of distribution and to identify possible transmission vectors. The answers, however, raise many new questions. In the present study, different wild fish species taken from carp ponds with a history of KHV infection were examined for their susceptibility to the virus. In the tissue of these fish, the virus load was determined and it was tested whether a release of the virus could be induced by stress and the virus then could be transferred to naive carp. Wild fish were gathered from carp ponds during acute outbreaks of virus‐induced mortality in summer and from ponds stocked with carp carrying a latent KHV infection. From these ponds, wild fish were collected during the harvesting process in autumn or spring when the ponds were drained. We found that regardless of season, temperature variation, age and infection status of the carp stock, wild fish from carp ponds and its outlets could be tested positive for the KHV genome using real‐time PCR with a low prevalence and virus load. Furthermore, virus transfer to naive carp was observed after a period of cohabitation. Cyprinid and non‐cyprinid wild fish can therefore be considered as an epidemiological risk for pond carp farms.     

What controls fish functional diversity patterns in Colombian Andean streams?

Understanding the mechanisms that structure communities have been a major challenge in ecological theory. Functional trait-based approaches are increasingly used for studying the processes underlying community assembly. However, species-poor systems of Andean streams these processes are largely unknown. Tropical Andean streams are highly variable in space-time and characterised by the harsh or stable environment, resulting in a high taxonomic and ecological diversity. In this study, we tested the influence of environmental variables on the fish functional structure. We proposed that in ecosystems with harsh environments, environmental filtering will structure fish assemblages, and in ecosystems with a more stable environment, limiting similarity will prevail, increasing functional diversity. We analysed fish assemblages using functional diversity indices, fourth-corner RLQ analyses and multiple regression models. Environmental variables such as altitude, stream width, sub-Andean vegetation and pH influenced functional diversity. For instance, high values of functional redundancy were registered at high elevation streams, reflecting fish assemblages composed of highly dominant species with similar functional traits such as species of the genus Astroblepus. However, we found differences between Astroblepus species in the number and distance of gill rakers which might indicate resource partitioning and coexistence. On the other hand, our results show both stochastic dynamics and environmental filtering are structuring fish assemblages in low and high elevation Andean streams respectively.     

Reinventing residual reserves in the sea: are we favouring ease of establishment over need for protection?

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Study of food web structure and trophic level in the sea ponds of an optimized culture model (jellyfish–shellfish–fish–prawn)

The food sources of the main economic animals and trophic levels of biotic communities from an optimized culture model (Rhopilema–Sinonovacula constricta–Paralichthys olivaceus–Penaeus chinensis) in a sea water pond in Donggang, Liaoning province were studied using the stable carbon and nitrogen isotopes technique. The results indicated that the values of δ¹³C range from (?27.28 ± 0.35) ‰ to (?16.65 ± 0.20) ‰ and the values of δ¹⁵N range from (3.68 ± 0.23) ‰ to (13.91 ± 0.26) ‰, both of which exhibited significant fluctuations. The δ¹³C values of P. chinensis, Macrobrachium mipponensis and P. olivaceus were comparatively higher than those of other aquaculture animals, and the δ¹⁵N values of P. olivaceus was also comparatively higher. The contribution to the food sources of aquaculture animals (Rhopilema, S. constricta, P. olivaceus and P. chinensis) was analyzed by using the IsoSource software. The results indicated that fish meat had the greatest contribution to Rhopilema, S. constricta and P. chinensis; P. chinensis had the greatest contribution to P. olivaceus, followed by the M. mipponensis. The trophic level of the biotic communities under that optimized culture model in a sea water pond was 3.54, in which P. olivaceus was in the fourth level (3.54); P. chinensis, Synechogobius hasta, Ablennes anastomella, M. mipponensis, Ditrema temmincki Bleeker, Chelon haematocheilus were in the third trophic levels; Rhopilema, Engraulis japonius, S. constricta and zooplankton (1.00) in the second trophic levels, suspended matters (0.15) including phytoplankton, bacteria, humus, etc., were in the primary trophic levels.     

Geographic, terrestrial and aquatic factors: which most influence the structure of stream fish assemblages in the midwestern United States?

Abstract – Effects of environmental or landscape factors on species composition, species richness and complexity of fish assemblages were examined using our collections of fish from 65 sites on streams in 13 drainages across the midwestern United States. Effects of environmental factors were examined at three scales: broad geographic factors included drainage, latitude, and longitude; local terrestrial factors included features of the riparian zone adjacent to the collecting site as well as local climate and land use; within-stream aquatic factors related to structure and hydrology of the stream reach sampled. Each assemblage property was examined for its relationship to factors at each scale separately, and then for relative importance of all factors found to be significant in the separate analyses. Assemblage composition (summarized as sample scores on two axes of a detrended correspondence analysis) varied significantly as a function of factors at all three scales when each scale was considered separately. With simultaneous consideration of all scales, however, only broad geographic factors (particularly latitude) and local terrestrial factors explained significant variation in assemblage composition. Species richness (the number of species we captured) was explained by longitude and within-stream aquatic factors both when considered separately and together. Assemblage complexity (quantified as slope of relative abundance versus rank abundance) was only related to within-stream aquatic factors. Assemblage composition and emergent assemblage properties (richness and complexity), therefore, were explained by factors acting at different scales. The total variation explained for assemblage composition was much greater than that explained for emergent assemblage properties, suggesting that assemblage composition may vary more as a function of environmental and landscape factors than do species richness and complexity. ^NOTE     

Cage fish culture in Lake Victoria: A boon or a disaster in waiting?

Fish catches in Lake Victoria have been on the decline while demand for fish has been increasing. Cage culture with >3,000 cages, over 3 million tilapias and valued at US$ 12 million is trying to fill the gap. This study reviews the development of cages and the need to develop a decision support tool for effective management. Existing literature and data on fisheries and cage culture held by the Kenya Marine and Fisheries Research Institute (KMFRI) were used in the analysis. Cage culture is a promising venture that may increase productivity, offer employment and enhance economic well‐being. However, site suitability for the installation of cages is poorly regulated with most developments (>45%) located within 200 m of the shoreline that are breeding grounds of fish and conflict with other lake users. Waste feed increases eutrophication, and enhances growth of algae and water hyacinth in the lake. Recent isolated fish kills were attributed to low dissolved oxygen concentrations (<0.64 mg/L), and an increasing occurrence of fish disease are signs of poor management practices among cage farmers. Cage culture may turn into an environmental disaster if not managed well, and there is need for robust policies and increased awareness to reduce environmental impacts.     

Can fish really feel pain?

We review studies claiming that fish feel pain and find deficiencies in the methods used for pain identification, particularly for distinguishing unconscious detection of injurious stimuli (nociception) from conscious pain. Results were also frequently misinterpreted and not replicable, so claims that fish feel pain remain unsubstantiated. Comparable problems exist in studies of invertebrates. In contrast, an extensive literature involving surgeries with fishes shows normal feeding and activity immediately or soon after surgery. C fiber nociceptors, the most prevalent type in mammals and responsible for excruciating pain in humans, are rare in teleosts and absent in elasmobranchs studied to date. A‐delta nociceptors, not yet found in elasmobranchs, but relatively common in teleosts, likely serve rapid, less noxious injury signaling, triggering escape and avoidance responses. Clearly, fishes have survived well without the full range of nociception typical of humans or other mammals, a circumstance according well with the absence of the specialized cortical regions necessary for pain in humans. We evaluate recent claims for consciousness in fishes, but find these claims lack adequate supporting evidence, neurological feasibility, or the likelihood that consciousness would be adaptive. Even if fishes were conscious, it is unwarranted to assume that they possess a human‐like capacity for pain. Overall, the behavioral and neurobiological evidence reviewed shows fish responses to nociceptive stimuli are limited and fishes are unlikely to experience pain.     

The effect of α-MSH treatment on the hypothalamic-pituitary-gonad axis in the cichlid fish Oreochromis mossambicus

Fish Physiology and Biochemistry - In this investigation, we examined the influence of alpha-melanocyte stimulating hormone (α-MSH), a proopiomelanocortin-derived peptide, along the...