Status and conservation of euryhaline fish in Irish waters

1. Ireland's fish fauna comprises at least 31 species that could be classified as euryhaline. This group includes 12 diadromous species, 3 non-migratory species, and 16 essentially marine and/or estuarine species. Twenty-four species are regarded as indigenous, 6 as occasional vagrants from other biogeographical zones and one was introduced by man during the last century. Fourteen species are considered to be widespread, 11 local, and 6 rare. 2. The biology of euryhaline fish makes them particularly vulnerable to any degradation of the coastal and estuarine environments. However, relatively few studies have been carried out on the biology and distribution of most species of Irish euryhaline fish. This lack of basic information is of particular concern, considering that 35% (11) of our euryhaline species are considered to be threatened. 3. Although 8 of our euryhaline species are listed in the Red Data Book on Irish Vertebrates(Whilde, 1993) and in various annexes and appendices of the Bern Convention (Anon, 1982) and EU Habitats Directive(Anon, 1992), only one of these species (Atlantic salmon Salmo salar L.) is currently afforded protection by any specific national legislation in Ireland. It is recommended that research should be directed at assessing the current status of our euryhaline fish and that appropriate national protection should be afforded to threatened species. ©1996 by John Wiley & Sons, Ltd.     

Links between riparian landcover,instream environment and fish assemblages in headwater streams of south‐eastern Brazil

We hypothesised and tested a hierarchical organisation model where riparian landcover would influence bank composition and light availability, which in turn would influence instream environments and control fish assemblages. The study was conducted during the dry season in 11 headwater tributaries of the Sorocaba River in the upper Paraná River Basin, south‐eastern Brazil. We focused on seven environmental factors each represented by one or multiple environmental variables and seven fish functional traits each represented by two or more classes. Multivariate direct gradient analyses suggested that riparian zone landcover can be considered a higher level causal factor in a network of relations that control instream characteristics and fish assemblages. Our results provide a framework for a hierarchical conceptual model that identifies singular and collective influences of variables from different scales on each other and ultimately on different aspects related to stream fish functional composition. This conceptual model is focused on the relationships between riparian landcover and instream variables as causal factors on the organisation of stream fish assemblages. Our results can also be viewed as a model for headwater stream management in that landcover can be manipulated to influence factors such as bank composition, substrates and water quality, whereas fish assemblage composition can be used as indicators to monitor the success of such efforts.     

Do spatial models of growth rate potential reflect fish growth in a heterogeneous environment? A comparison of model results

Abstract – Spatial models of fish growth rate potential have been used to characterize a variety of environments including estuaries, the North American Great Lakes, small lakes and rivers. Growth rate potential models capture a snapshot of the environment but do not include the effects of habitat selection or competition for food in their measures of environment quality. Here, we test the ability of spatial models of fish growth rate potential to describe the quality of an environment for a fish population in which individual fish may select habitats and local competition may affect per capita intake. We compare growth rate potential measurements to simulated fish growth and distributions of model fish from a spatially explicit individual-based model of fish foraging in the same model environment. We base the model environment on data from Lake Ontario and base the model fish population on alewife in the lake. The results from a simulation experiment show that changes in the model environment that caused changes in the average growth rate potential correlated extremely highly ( r ²≥0.97) with changes in simulated fish growth. Unfortunately, growth rate potential was not a reliable quantitative predictor of simulated fish growth nor of the fish spatial distribution. The inability of the growth rate potential model to quantitatively predict simulated fish growth and fish distributions results from the fact that growth rate potential does not consider the effects of habitat selection or of competition on fish growth or distribution, processes that operate in our individual-based model and presumably also operate in nature. The results, however, do support the use of growth rate potential models to describe the relative quality of habitats and environments for fish populations.     

Perceptual constraints on stream fish habitat selection: effects of food availability and water velocity

Abstract– Habitat selection theory assumes that individuals either know the quality of habitats a priori or can learn it through experience. This work tests the effects of total food supply and of water velocity on the ability of drift-feeding stream fish ( Rhinicthys atratulus ) to discriminate between two patches in a laboratory flow-tank that differ only in the amount of food in the patch. If the fish can discriminate between the patches, their distributions should be predicted by ideal free distribution models; otherwise, their distributions should be random. The results show that at high total food supply levels, fish distributions differ from random in general agreement with ideal free distribution models; total food supply decreases, fish distributions become random, indicating that total food supply levels affect the ability of fish to discriminate between habitats that differ only in food supply. Increased water velocity was expected to affect fish distributions similarly, but its effect was not significant. The results suggest that habitat selection theory should consider both differences between habitats and the ability of fish to perceive those differences.     

滇池食蚊鱼胚胎发育特点及与母体的营养联系

卵胎生是鱼类为适应特定环境进化出的一种生殖策略。食蚊鱼(Gambusia affinis)是典型的卵胎生鱼类,厘清其卵胎生特征是否在入侵云贵高原过程中发生适应性演化的问题,有助于深入了解其种群快速扩散机制。本研究用常规解剖观察法、称重法,针对滇池种群胚胎发育特点、干湿重变化及与母体营养联系问题开展研究。结果显示,滇池食蚊鱼胚胎发育过程依赖于卵黄营养供给,在产出前,卵黄仅微量残余,身体发育完善,基本保持了物种固有的卵胎生特点。胚胎湿重在胚胎发育过程中显著增加,但同时干重损失也十分明显(30.4%),营养指数(MI)为0.70,提示母体对胚胎没有受精后的特定营养供给,支持食蚊鱼是严格意义上的卵磷脂营养型(卵胎生)鱼类观点。其胚胎(仔鱼)出现小型化趋势,胚胎湿重、干重及初生体长等关键生态适应性性状明显低于已研究的其他低地种群,表现出对高原环境的适应性响应。这种响应是否有助于其向更高海拔的高原环境扩散值得进一步深入研究。     

Genetic improvement of farmed tilapias: Composition and genetic parameters of a synthetic base population of Oreochromis niloticus for selective breeding

The present study is based on data recorded from fish of the third generation of the GIFT project (Genetic Improvement of Farmed Tilapias). The objective of the study was to compose a synthetic base population of Nile tilapia for further selective breeding, and to estimate phenotypic and genetic parameters in that population. The base population was formed by choosing parent stock among the best performing animals within the best strain combinations resulting from a full diallel cross design (8 × 8) involving four African wild strains and four Asian farmed strains (64 strain combination cells altogether). The grandparent ancestors of the base population were mainly representing the three strains originating from Egypt, Kenya and Thailand (20.2, 27.3 and 19.6%, respectively). The proportion of ancestors from the Senegal strain was medium (12.2%) whereas the proportion of ancestors from Ghana, Israel, Singapore and Taiwan strains was low (3 to 8%) and mainly due to a restriction that all parent strains should be represented in the synthetic base. Statistical analyses using a mixed animal model were carried out on records from 13,570 individually tagged and surviving progeny of 50 sires and 123 dams. The growth performance of the fish was tested in seven diverse environments. The test environments covered a wide range of tilapia farming systems, namely, earthen ponds fertilized with inorganic fertilizer and organic manure or on-farm agricultural residues, cage culture, and test stations located in different agro-climatic regions. The model fitted included the fixed effect of test environment and sex and the linear and quadratic covariate of age at stocking. The random terms were the additive genetic effect of individual fish and the additional effects common to full-sib groups. The estimates of heritability for body weight at harvest in different test environments ranged from moderate to high (0.12 to 0.56) and the estimate across test environments was 0.15. The variances due to other effects common to full-sib families were significant, accounting for 8 to 16% of total variation in body weight. The genetic correlations among body weights recorded in similar environments were high (mostly > 0.80, i.e. among the earthen ponds in experimental locations). By contrast, the genetic correlations between harvest weight in earthen pond and in cage environments were more variable (0.36-0.82). Overall, the results suggested that the genotype by environment interactions were of limited importance, at least for the target pond farming systems in the Philippines. It was concluded that as the additive genetic variation in the base population was large, the harvest weight of the GIFT fish could be effectively improved by selective breeding, and that there was no immediate need to develop separate strains for different environments.     

Low-salinity tolerance of juvenile fugu <Emphasis Type="Italic">Takifugu rubripes</Emphasis>

ABSTRACT:   To study the adaptability of juvenile fugu Takifugu rubripes to low-salinity environments, fish were transferred from full-strength seawater (100% SW) to freshwater (FW) and 25, 50, 75 and 100% SW, and checked for mortality over 3 days. No mortality was observed in 25–100% SW, whereas all fish died in FW. In fish transferred to 25–100% SW, blood osmolality was maintained within a physiological range. To further explore the lower limit of salinity that fugu could tolerate, fish were transferred from 100% SW to FW and 1, 5, 10, 15 and 25% SW. All fish survived in 5–25% SW, but fish died in FW and 1% SW. In fish surviving transfer to FW and 1 and 5% SW, blood osmolality was decreased to a near sublethal level of approximately 300 mOsm/kg·H₂O. Therefore, the lower limit of salinity tolerance is estimated to lie between 5 and 10% SW. Preacclimation in 25% SW for 7 days did not essentially affect the survival salinity range. Although survival rates and blood osmolality were slightly improved by preacclimation in 25% SW, blood osmolality was markedly decreased in salinities less than 10% SW, as was seen in the direct transfer. Neither chloride cell morphology nor sodium-potassium adenosinetriphosphatase activity in the gills showed a significant change following transfer to low salinities. These findings indicate that fugu can be adapted to hypoosmotic environments to some extent, exerting hyperosmoregulatory ability, although chloride cells are less likely to absorb ions in hypoosmotic environments.     

Living in an amphidromous world: Perspectives on the management of fish passage from an island nation

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Generalist feeding strategies in Arctic freshwater fish: A mechanism for dealing with extreme environments

Generalist feeding strategies are favoured in stressful or variable environments where flexibility in ecological traits is beneficial. Species that feed across multiple habitat types and trophic levels may impart stability on food webs through the use of readily available, alternative energy pools. In lakes, generalist fish species may take advantage of spatially and temporally variable prey by consuming both benthic and pelagic prey to meet their energy demands. Using stomach content and stable isotope analyses, we examined the feeding habits of fish species in Alaska's Arctic Coastal Plain (ACP) lakes to determine the prevalence of generalist feeding strategies as a mechanism for persistence in extreme environments (e.g. low productivity, extreme cold and short growing season). Generalist and flexible feeding strategies were evident in five common fish species. Fish fed on benthic and pelagic (or nektonic) prey and across trophic levels. Three species were clearly omnivorous, feeding on fish and their shared invertebrate prey. Dietary differences based on stomach content analysis often exceeded 70%, and overlap in dietary niches based on shared isotopic space varied from zero to 40%. Metrics of community‐wide trophic structure varied with the number and identity of species involved and on the dietary overlap and niche size of individual fishes. Accumulation of energy from shared carbon sources by Arctic fishes creates redundancy in food webs, increasing likely resistance to perturbations or stochastic events. Therefore, the generalist and omnivorous feeding strategies employed by ACP fish may maintain energy flow and food web stability in extreme environments.     

Exploring the trophic structure in organically fertilized and feed-driven tilapia culture environments using multivariate analyses

Reports of similar yields in manure and feed‐driven tilapia culture environments raise questions on food utilization in these environments. The possibility that similar production rates are because of utilization of different foods was investigated using exploratory techniques of multivariate analyses. Using factor analysis, trophic pathways through which food becomes available to fish were explored, and using anova models, water quality, sediment quality and tilapia growth and yields were compared. Conceptual graphic models of the main ecological processes occurring in feed‐driven and organically fertilized environments are presented and discussed. In both environments, autotrophic and heterotrophic pathways are important processes that result in the availability of natural foods that are utilized by the fish. Extrapolated fish yield data indicate that with equal nutrient input and stocking density, organically fertilized environments could achieve production rates similar to those in feed‐driven environments. The general assumption that supplemental or complete foods are well utilized by tilapia in outdoor stagnant ponds remains challenged, and further research on tilapia feeding behaviour and food selection in feed‐and organic fertilizer‐driven environments is needed.     

Methods for studying spatial behaviour of freshwater fishes in the natural environment

Spatial behaviour of fishes in fresh and brackish water ranges in temporal scales between localized diel movements, often associated with foraging and predator evasion, to seasonal or life‐cycle related events involving movements between freshwater habitats or freshwater and marine biotopes. Recent technological advances have resulted in dramatic improvements in the range of techniques available for the study of spatial behaviour of freshwater fishes in the natural environment, and broadly may be divided into two categories: capture dependent and capture independent. The former incorporates those methods that rely on sampling marked fish (mark–recapture) or unmarked fish (density estimates, catch per unit effort) over defined scales of time and space in order to derive information on distribution and movement. Captured fish may also be tagged with transmitters that radiate energy, enabling the fish to be tracked and/or environmental data to be gathered. Biochemical analysis of samples from fish, requiring non‐destructive sampling (genetic analysis and scale microchemistry) or destructive sampling (otolith microchemistry) may also provide information on migration and ontogenetic processes. Capture independent techniques include visual observation and video techniques, hydroacoustics and automated fish counting. Catch per unit effort and mark–recapture techniques are most efficient where long‐term fishery or monitoring studies are in place and data on crude spatial and temporal scales are acceptable. They also have the advantages of low technical requirements and low equipment costs. Where specific management or ecological questions are pertinent, recapture independent techniques may be more appropriate. Telemetric methods can provide high resolution information at the individual level, while hydroacoustics is increasingly providing information at the population level in large lake and river environments. Biochemical methods are becoming increasingly useful in determining the extent of population segregation, where DNA analysis is used, and in the study of migration and ontogenetic changes in behaviour, where otolith microchemistry and stable isotope analysis is used.     

Breeding Programs for Sustainable Aquaculture

ABSTRACT

Definition of breeding goals for sustainable fish production is considered, with emphasis on non-market (e.g., ethical) as well as market values. The need for long-term biologically, ecologically, and sociologically sound breeding goals is emphasized, because animal breeding determined only by short-term market forces has lead to unwanted side effects. Farmed fish is at an early stage of domestication and breeding, but rapid selection responses for growth have already been documented for several species. Reports of selection responses for fish and shellfish in both temperate and tropical environments are reviewed. Growth-rate responses of 4-20% have been obtained per generation. Broad breeding goals, including health and functional traits, in addition to production traits, are required. More basic knowledge of, e.g., animal welfare and behavioral disorders of fish is also needed.

Less than 1% of the aquaculture fish material in 1993 originated from selection programs. For most species under improvement, only one or very few programs are running, and the effective population sizes are often limited. Such populations may however easily gain sufficient advantage above non-improved populations to capture much of the market.

This will also discourage further genetic introductions into the breeding nucleus. Long-term inbreeding and loss of genetic variability because of genetic drift may then affect performance and further genetic progress. A sufficiently large and genetically diverse breeding population with appropriate family structure is therefore fundamental when establishing and running a selection program.

Important prerequisites for breeding programs for sustainable production are appropriate governmental policies and awareness of our way of thinking about aquaculture, nature and society. A more communal worldview informed by a subjective epistemology (how we learn about/ analyze nature) and a holistic ontology (belief about what/how nature is) is also required.     

Methods for identification and differentiation of different Shewanella spp. isolates for diagnostic use

Shewanella spp. are Gram‐negative, rod‐shaped, motile bacteria that are widely distributed in marine and freshwater environments. The bacteria are present in the physiological microflora of fish from temperate waters and are known as fish spoilage species. From clinically healthy fish and from fish with skin ulcerations, Shewanella spp. is regularly isolated, indicating a possible role as fish pathogen. In this study, 74 isolates of Shewanella spp. were analysed. For species identification, biochemical techniques, 16S rRNA sequencing, MALDI‐TOF MS and the Sherlock Microbial Identification System (MIS) based on the composition of fatty acid ethyl esters were compared. The phylogenetic relationship, cytotoxicity in vitro and resistance against antibiotics were tested. The most reliable method for species identification was 16S rRNA sequencing. From diseased fish, clinically healthy fish and the aquatic environment, different Shewanella species were isolated. This indicates that Shewanella spp. is widespread in the aquatic milieu and acts as a secondary pathogen. The virulence of Shewanella spp. is probably not depending on the species but on the isolate itself. Many isolates of Shewanella spp. were showing multiresistances against antibiotic substances, especially in samples derived from retailers and in routine diagnostics, all Shewanella spp. should therefore be tested for resistances against antibiotic agents.     

深水网箱养鱼业的现状与发展趋势

深水网箱是指设置在相对较深海域,养殖容量较大,具有较强的抗风浪、流性能的海上养殖设施。它在拓展养殖海域、减轻沿岸环境压力、提高养殖鱼的质量、增加养殖效益等方面已显示出明显的优势。由于它是新兴的一种设施渔业,能包容的高新技术多,涉及材料、机械、电子、苗种、饲料、环境等诸多方面,当前仍有不少技术问题需要解决。建议今后对此产业加强宏观管理和指导,改进设施,改善管理,加强科技投入,提高业者素质,扩大经营规模,提高产品质量,借鉴世界上渔业发达国家的经验,使这一产业健康、持续发展。     

Development of a novel PCR assay based on the 16S-23S rRNA internal transcribed spacer region for the detection of Lactococcus garvieae

Lactococcus garvieae is recognized as an emerging pathogen in fish. Several PCR‐based methods have been developed for the detection and identification of L. garvieae; however, the sensitivity of these methods is still in question regarding the discrimination of this organism from other closely related species. Two primers, ITSLg30F and ITSLg319R, were designed from the sequence in the 16S–23S internal transcribed spacer (ITS) region and used for the specific detection of L. garvieae. L. garvieae strains including fish isolates were positive by this method. In contrast, previously developed PCR methods showed false‐positive results with non‐L. garvieae species. Our results indicate that a PCR method using the newly designed ITS primer set provides a sensitive and efficient tool for the detection of L. garvieae in fish and aquaculture environments.     

Sex‐dependent responses of perch to changes in water clarity and temperature

Rising temperatures and decreasing water transparency of lakes have strong wide ranging effects on fish. Fish responses to various changes in the environment are usually species‐dependent, but responses may also vary within species. In general, large individuals are considered to be more sensitive to environmental variation due to higher energy demand, than smaller individuals. Similarly, large individuals require more food to maintain bodily functions and are thus more sensitive to resource and food scarcity. These size‐specific responses to environmental gradients are also sex‐dependent in species that exhibit sexual size dimorphism (SSD). We studied in enclosures with short‐term experiments how rising temperatures and decreasing water transparency regulate the feeding rates of female and male European perch (Perca fluviatilis L.). To explore experimental results, we calculated perch SSD in nine lakes with varying environmental conditions using previously collected field data. The results of the experiments revealed that the combined effect of water transparency and temperature on the feeding rate of fish is gender‐dependent: feeding rate of females decreased more than that of males. The experimental results were also supported by field data that revealed a negative relation between water transparency and the magnitude of SSD in perch. Our results suggest that rising temperatures and decreasing water transparency may potentially decrease fish size in a sex‐dependent manner. As female size is one of the main demographic traits determining the reproductive success of a fish population, changing environments may have unexpected and far‐reaching consequences on fish population dynamics.     

Unravelling the complex habitat use of the white mullet,Mugil curema,in several coastal environments from Neotropical Pacific and Atlantic waters

1. The white mullet, Mugil curema, is a widely distributed euryhaline species, the migratory behaviour of which is poorly understood. The objective of this work was to study the large-scale habitat use of this species for the first time. Several environments were considered, such as euryhaline and hypersaline lagoons, the sea, and a river, distributed in the Central Pacific (Mexico) and Atlantic (Gulf of Mexico, Caribbean Sea-Venezuela, and north-eastern Brazil).
2. Otolith core-to-edge Sr/Ca ratios of 163 fish, determined by laser ablation inductively coupled plasma mass spectrometry, were used to study the salinity-habitat migration history of the fish. Fish from Mexico (Tamiahua Lagoon, n = 4; Alvarado Lagoon, n = 2), Venezuela (n = 1), and Brazil (n = 12) (11.1% of the total) showed high Sr/Ca values at early life stages and were classified as marine estuarine opportunists. Two specimens (from Alvarado Lagoon and Balsas River, Mexico) showed Sr/Ca values consistently below the high salinity guide value (salinity < 33.5). For the rest of the fish (87.1%), the Sr/Ca ratio suggested a displacement from the estuary towards the sea or hypersaline environments, and so these fish were classified as estuarine migrants.
3. A change-point analysis identified six individuals with a single stable otolith Sr/Ca signature through ontogeny (three from Brazil, one from Venezuela, and two from Tamiahua Lagoon, Mexico), suggesting limited displacement between environments with different salinities. The rest of the individuals showed between two and 10 changes in stable Sr/Ca signatures (mean = 4.07 ± 1.85). The highest number of changes in Sr/Ca ratio (4.87 ± 1.1) was found in fish from Laguna Madre (Mexico) and the lowest was found in fish from Brazil (3.27 ± 1.70) (H = 19.8, p = 0.002).
4. Otolith Sr/Ca time series suggest that the migratory estuarine pattern is the most common throughout the study area. This work highlights that the sustainable use of M. curema depends on the conservation of estuaries and the corridors between them and other environments such as lagoons, rivers, mangroves and the sea.

     

Fish telemetry in aquaculture: review and perspectives

The assessment of the behaviour or physiology of cultured fish has always been difficult due to the timing of sampling, differences between experimental and aquaculture conditions and to methodological bias arising from repeated fish handling. The development of biotelemetry techniques offers a wide range of possibilities to improve both production and management in aquaculture through monitoring of behaviour or physiology of free-swimming fish inside their culture environment. Thus knowing how key parameters are changing can allow faster adjustment of feeding times to activity rhythms, more objective identification of the preference/tolerance margins towards environmental variables and precise assessment (from the fish's point of view) of the impact of environmental or operational stressors on fish. This paper briefly reviews the techniques that might be applied in aquaculture and focuses on relevant systems and estimators of fish activity: movements, vertical distribution, use of demand-feeders, muscular activity and heart rate. Species or size-related limitations and use of automatic monitoring stations are reviewed and evaluated. Perspectives of integrated biomonitoring in aquaculture are discussed, using telemetered fish as reliable probes in the detection of abnormal situations such as changes of water quality or altered environments.     

Integration of sonar and optical camera images using deep neural network for fish monitoring

Fish monitoring in aquaculture farms is indispensable for managing the growth and health status of fish resources. However, it is unrealistic to expect humans to be able to perform monitoring at night, when standard optical cameras are generally inapplicable. Although sonar systems can be used at night, their practical applications are limited by their monochrome, low-quality images. In this paper, we describe a realistic image generation system that uses sonar and camera images recorded at night. The proposed approach is based on conditional generative adversarial networks, which learn the image-to-image translation between sonar and optical images. We tested the system in a fish tank containing thousands of sardines (Sardinops melanostictus). Images were simultaneously recorded using high-precision imaging sonar and an underwater camera. Experimental results show that the proposed model successfully generates realistic daytime images from sonar and night camera images. Our system enables nighttime monitoring using sonar and an optical camera, leading to more efficient fish farming and environmental surveillance.     

Developmental temperature affects phenotypic means and variability: A meta‐analysis of fish data

Fishes are sensitive to their thermal environment and face an uncertain future in a warming world. Theoretically, populations in novel environments might express greater levels of phenotypic variability to increase the chance of surviving—and eventually thriving—in the new conditions. Most research on the effect of the early thermal environment in fish species focuses on average phenotypic effects rather than phenotypic variability, but to understand how fishes will respond to rising temperatures we need to consider both the average response of the population, as well as the breadth of individual responses. Here we present the first meta‐analysis on the effects of developmental temperature in fishes. Using data from 43 species and over 6,000 individual fish, we show that a change in developmental temperature induces a significant change in phenotypic means and variability, but differently depending on whether the temperature is increased or decreased. Decreases in temperature (cool environments) showed a significant decrease in phenotypic means and no change in phenotypic variability. Increases in temperature (warm environments) showed a non‐significant increase in phenotypic means and a marginally significant increase in phenotypic variability. Larger increases in temperature saw greater increases in phenotypic variability, but no increase in the mean phenotypic response. Together, our results suggest that fishes exhibit both directed and stochastic developmental plasticity in response to warming temperatures, which could facilitate or accelerate adaptation to a changing environment.