The application of molecular markers to the study and conservation of fish populations, with special reference to Salmo

The main molecular techniques which can be used to generate genetic markers, and the applications of these markers to studies of fish populations are outlined. Published and ongoing studies, in the authors' laboratories, on brown trout and Atlantic salmon are used to compare the resolution and applicability of allozyme, mitochondrial DNA and minisatellite (variable number of tandem repeats) markers for studies on population structuring, genetic variation within populations, and the impact of the accidental and deliberate introduction of non-native salmonids on the genetic make-up of natural populations.     

The nutrition of stomachless phytoplanktivorous fish in comparison with Tilapia

The contents of alimentary tracts of stomachless phytoplanktivorous fish, including silvercarp (Hypophthalmichthys molitrix), Esomus danrica thermoicos, and Amblypharyngodon meletinus were investigated microscopically and compared with those of Tilapia (Oreochromis mossambicus, a fish with stomach).The predominance of detritus in the food and the low efficiency with which phytoplankton is utilized prove, that stomachless fish are not primarily herbivorous. The possibility of omnivorous feeding as an alternative is discussed. These results may contribute to our understanding of the role of filterfeeders in aquaculture and ecosystems.     

Dietary self-selection in fish: a new approach to studying fish nutrition and feeding behavior

The principles of modern aquaculture encourage the development of fish feeds containing low fish meal content and several types of plant ingredients plus nutrients to avoid depleting global fish stocks and to reduce costs. However, food constituents can affect animal nutrition and feeding behavior, so the effect of different diets on fish behavior and growth needs to be understood to optimize the use of nutrients and to improve fish welfare. The development of multiple-choice self-feeding systems led to a new perspective for investigating these issues in aquaculture species. Our purpose with this review is to summarize the information that has been published to date on this topic and to identify gaps in knowledge where research is needed. Key subjects are assessed under the following major headings: How do we study dietary selection in fish? What food signals do fish use to choose the right diet? and How do fish respond to food challenges? The present review will provide a picture of the main results obtained to date in these studies in aquaculture fish species, as well as perspectives for future research in the field.     

Proteinases of potential objects of fish nutrition

The review analyzes data on activities and characteristics of proteinases of digestive system and of cathepsins of various tissues in potential preys of fish differing by the character of nutrition. There are presented data on multiple forms and molecular mass of proteinases, species-related differences, dependence of proteinase activities on the life cycle stages, type of nutrition, and biochemical food composition as well as on temperature and pH optima. Role of cathepsin in evolution of enzymatic systems providing degradation of food protein components in fish is discussed.     

A review of some fish nutrition methodologies

Several classical warm blooded animal (poultry, sheep, cows, etc.) methods for dietary nutrients evaluation (digestibility, metabolizablity, and energy budget) are applied to fish, even though fish live in a different environment in addition to being cold blooded animals. These applications have caused significant errors that have made these methods non-additive and meaningless, as is explained in the text. In other words, dietary digestion and absorption could not adequately be measured due to the aquatic environment fish live in. Therefore, net nutrient deposition and/or growth are the only accurate measurement left to evaluate dietary nutrients intake in fish. In order to understand and predict dietary nutrient intake-growth response relationship, several mathematical models; (1) the simple linear equation, (2) the logarithmic equation, and (3) the quadratic equation are generally used. These models however, do not describe a full range of growth and have no biological meaning as explained in the text. On the other hand, a model called the saturation kinetic model. It has biological basis (the law of mass action and the enzyme kinetic) and it describes the full range of growth curve. Additionally, it has four parameters that summarize the growth curve and could also be used in comparing diets or nutrients effect on fish growth and/or net nutrient deposition. The saturation kinetic model is proposed to be adequate for dietary nutrient evaluation for fish. The theoretical derivation of this model is illustrated in the text.     

Protein nutrition in fish: protein/energy ratio and alternative protein sources to fish meal

Those interested in the design and manufacture of feeds for intensive fish farming face the basic concern of formulating mixtures for the best yield at the lowest costs. Of the macronutrients in the feed, protein has and continues to receive special consideration because fish present high and specific needs for this constituent. Traditionally, protein has been supplied primarily by fish meals. This paper presents a synthesis of the efforts made and the lines explored to achieve an effective reduction of the amount of fish meal in the feeds for fish, following two strategies: reduction of the protein in the feeds and the use of new raw materials to replace fish meal.     

Endocrine control of nutrition in cyclostomes and fish

• 1.1. The relationship between nutritional patterns and physiological levels of endogenous hormones, in some species of cytosomes and fish, is studied.
• 2.2. Most of the observations are related to species showing a marked life cycle, including natural fasting periods and migrations.
• 3.3. Insulin seems to play a major role in regulating the nutritional metabolism, which appears to be largely dependent on gluconeogenesis and on amino acids supply.

     

The application of image cytometry to viability assessment in dual fluorescence-stained fish spermatozoa

The viability of spermatozoa has been assessed using SYBR 14 staining for DNA of living cells and propidium iodide staining for DNA of degenerate cells. This dual staining was performed on four fish species (Siberian sturgeon, Acipenser baerii; common carp, Cyprinus carpio; tench, Tinca tinca and wels, Silurus glanis) and the proportions of live and dead spermatozoa were assessed by epifluorescence microscopy and image cytometry. Ten phase contrast and epifluorescent images were recorded per sample, corresponding images were overlaid, and the blended images were evaluated for live and dead spermatozoa, represented by green and red fluorescence signals. Live/dead proportions were assessed, after dual thresholding, by imaging software that counted absolute numbers of objects and computed their frequencies. All sperm heads were found to be labelled, emitting either green or red light. Mean numbers of spermatozoa per image were in the ranges 32-113, 61-105, 48-104 and 29-91 for Siberian sturgeon, common carp, tench and wels, respectively. The corresponding proportions of live spermatozoa were in the ranges 83.56-94.59%, 93.92-97.02%, 76.14-97.76% and 79.45-83.76%. Standard deviations did not exceed 5% of the means. The image cytometric system using dual staining with SYBR 14 and propidium iodide was clearly suitable for assessing the viability of freshwater fish spermatozoa.     

Spatial analysis of stable isotope data to determine primary sources of nutrition for fish

Carbon and nitrogen stable isotopes were used to determine the ultimate autotrophic sources supporting production of three commercially important fish species over unvegetated mudflats in a subtropical estuary. Mean isotope values over the whole estuary for fish and autotroph sources were modeled to indicate feasible combinations of sources. Variability in isotope values among nine locations (separated by 3-10 km) was then used as a further test of the likelihood that sources were involved in fish nutrition. A positive spatial correlation between isotope values of a fish species and an autotroph indicates a substantial contribution from the autotroph. Spatial correlations were tested with a newly developed randomization procedure using differences between fish and autotroph values at each location, based on carbon and nitrogen isotopes combined in two-dimensional space. Both whole estuary modeling and spatial analysis showed that seagrass, epiphytic algae and particulate organic matter in the water column, including phytoplankton, are likely contributors to bream (Acanthopagrus australis) nutrition. However, spatial analysis also showed that mangroves were involved (up to 33% contribution), despite a very low contribution from whole estuary modeling. Spatial analysis on sand whiting (Sillago ciliata) demonstrated the importance of two sources, mangroves (up to 25%) and microalgae on the mudflats, considered unimportant based on whole estuary modeling. No spatial correlations were found between winter whiting (Sillago maculata) and autotrophs, either because fish moved among locations or relied on different autotrophs at different locations. Spatial correlations between consumer and source isotope values provide a useful analytical tool for identifying the role of autotrophs in foodwebs, and demonstrated here that both in situ production of microalgae and organic matter from adjacent habitats were important to fish over mudflats.     

PIT telemetry as a method to study the habitat requirements of fish populations: application to native and stocked trout movements

Passive integrated transponder (PIT) technology was used to study the behaviour of fishes during the summer season in two headwater streams of northeastern Portugal. A total of 71 PIT tags (12 mm long × 2.1 mm diameter) were surgically implanted in 1⁺ stocked (39) and native (32) brown trout of two size classes (<20.0 and ≥20.0 cm). Eight independent antennae, connected to a multi-point decoder (MPD reader) unit, were placed in different microhabitats, selected randomly every 3 days during the observation period (29 August–9 September in Baceiro stream and 19 September–4 October in Sabor stream). The results confirmed this method as a suitable, labour efficient tool to assess the movement and habitat use of sympatric stocked and native trout populations. About 76.9% of stocked and 59.4% of native PIT tagged trouts were detected. Multivariate techniques (CCA, DFA and classification tree) showed a separation in habitat use between the two sympatric populations. Stocked trout mainly used the microhabitats located in the middle of the channel with higher depths and without cover. Furthermore, these fishes displayed a greater mobility and a diel activity pattern different to native trout populations.     

The application of flow microcalorimetry to the study of enzyme kinetics

The use of flow microcalorimetry to measure velocities for enzyme-catalyzed reactions is described. Studies are presented involving the enzymes chymotrypsin, trypsin, and ribonuclease A. In determining the Michaelis-Menten parameters, V_m and K_m, for these systems complications arise due to substrate depletion and product inhibition. By employing an integrated Michaelis-Menten equation, V_m and K_m can be determined.     

Planktonic and symbiotic organisms in nutrition of coralobiont fish

Nutrition of coral reef fish closely associated with the colonies of scleractinian corals Acropora spp. (South China Sea, Gulf of Nha Trang) was investigated. Parabionts Dascyllus reticulatus and Chromis caeruleus (Pomacentridae) feed mainly on zooplankton in the water column above the hosts’ colony, and inbionts Gobiodon quinquestrgatus (Gobiidae) rarely leave a host colony and feed generally on coral reef invertebrates. A high part of secondary nutrition objects (on average 19–29%) that indicates deficiency in main food were noted in both categories of fish. Food of all three fish species contains parasites (from 19% in C. caeruleus and up to 25% in G. quinquestrigatus) whose significant part is represented by parasites of coral (approximately 7% in D. reticulatus and C. caeruleus and 15% in G. quinquestrigatus). In addition, larvae of parasites of Isopoda and Facetotecta that are fed by fish in the water column were found. Mucus from the surface of host coral which was recognized on the basis of a high number of nematocysts in fish stomachs was found in food of G. quinquestrigatus for the first time. Positive and negative effects of symbiosis of fish and host-coral were discussed. A commensal character of symbiosis was supposed.     

鱼类线粒体DNA及其在分子群体遗传研究中的应用

鱼类是脊椎动物亚门中种属数量最多的类群,分布广泛,起源复杂,拥有丰富的遗传多样性.多种自然和人为因素对鱼类遗传资源存在不同程度的作用,对鱼类生存和进化有重要影响.采用分子手段探讨鱼类遗传资源现状,可为遗传育种、鱼类进化研究和遗传资源保护等提供一定科学依据.以鱼类线粒体DNA(mtDNA)为代表的分子标记技术已被用于研究鱼类群体遗传结构及其与影响因素间的关系.本文综述了鱼类mtDNA的结构特征及其在鱼类分子群体遗传研究中的应用,对了解和运用mtDNA等分子标记研究鱼类群体遗传具有一定参考价值.     

Some experimental approaches to the study of nutrition and parasitic infection

Two experimental models to examine the relationship between host nutrition and parasitic infection are considered. Moniliformis dubius, an acanthocephalan parasite of the laboratory rat, is dependent on the type and amount of host dietary carbohydrate for growth and reproduction. Starch, glucose, fructose, and mannose in host diets support parasite growth and development, but much lower dietary amounts of starch, fructose, and mannose are needed compared to free glucose. The pig-Ascaris suum relationship is considered as a model for human ascariasis. Experimental Ascaris infections in pigs resulted in reduced growth, reduced food intake, lowered biological value of dietary protein, and reduced intestinal lactase activity and lactose tolerance. These results are similar in some respects to reported effects of Ascaris infection in humans.     

Comparative analysis of reproductive traits in 65 freshwater fish species: application to the domestication of new fish species

Based on an extensive literature search (1,000 references), the objectives of the present study were to establish a numerical clustering of temperate freshwater fish based on their reproductive traits and to evaluate whether it was possible to extrapolate zootechnical knowledge among species belonging to the same cluster. About 65 species were classified into ten homogeneous clusters from the analysis of 29 reproductive traits, among which the most important were temperature during spawning, egg incubation and larval rearing, degree-days for incubation, larval size upon hatching, spawning season, and parental care. From this typology, a rather regular continuum of reproductive clusters emerges with two obvious endpoints. Between these two extremes, species could be ordered chiefly according to temperature requirement, spawning season and parental care. In conclusion, this new typology, differing significantly from all others proposed earlier, may now serve as a possible framework to help enhancing the domestication of new species by comparison to species belonging to the same cluster.