The ornamental fish trade and fish conservation

The global trade in ornamental fish and associated aquarium and pond accessories is in excess of U.S. $7 × 10⁹ each year. Although the majority of freshwater fish involved in the trade are from captive-bred sources, significant numbers are still removed from the wild. In addition, almost all of the marine fish in the trade are wild-caught. Whilst habitat destruction, pollution and overfishing for food are the main threats facing fish populations in the wild, the ornamental fish trade may have adverse effects as a result of the introduction of nonnative organisms, and by the direct depletion of wild stocks. The ornamental fish trade is ideally placed to raise public awareness of, and actively support, fish conservation efforts, and must maintain a close liaison with legislative-forming organizations seeking to impose further trade restrictions.     

观赏鱼

观赏鱼多姿多彩,从我国饲养观赏鱼概况、常见的几种观赏鱼、观赏鱼的饲养、与人类关系4方面介绍观赏鱼。     

Transgenic fish

Transgenic fish are produced by the artificial transfer of rearranged genes into newly fertilized eggs. Currently microinjection is the preferred method, although the integration rates of transgenes are generally low. A number of fusion genes, containing retrovirus sequences which direct integration, have been developed to enhance integration of transgenes. Mass gene transfer methods are also being developed. These include lipofection, particle bombardment, and electroporation of embryos and sperm cells. These methods are potentially useful for marine organisms such as crustaceans and molluscs as well as fish. In contrast to microinjection, which treats single cells individually, these methods can transfer genes into a large number of eggs at once. There is some evidence to indicate successful integration and expression of transgenes transferred by the electroporation of embryos and sperm cells. Germline transmission of transgenes has been observed through mating studies, and in some cases the progeny express the new phenotype consistently. However, germline transmission does not necessarily confirm stable integration of the transgene. There is evidence that transgenes may exist extrachromosomally. Transgenic fish are viewed as a useful model for the study of complex biological phenomena such as growth and differentiation, and as a fast track to the production of broodstock for the aquaculture industry. Current research focuses on the elucidation of the mechanisms controlling the regulation of gene expression. The use of transgenic fish for the isolation of developmental genes has just begun. Applications of transgenesis to broodstock development have been focused on the development of fish with accelerated growth, tolerance to low temperature, and disease resistance. However, before the release of transgenic fish into the environment, the possible impact on the environment must be assessed. There must be safeguards to protect the genetic diversities of the natural populations, and to conserve the natural habitats     

Small fish, big fish, red fish, blue fish: size-biased extinction risk of the world's freshwater and marine fishes

Aim  In light of the current biodiversity crisis, there is a need to identify and protect species at greatest risk of extinction. Ecological theory and global-scale analyses of bird and mammal faunas suggest that small-bodied species are less vulnerable to extinction, yet this hypothesis remains untested for the largest group of vertebrates, fish. Here, we compare body-size distributions of freshwater and marine fishes under different levels of global extinction risk (i.e. listed as vulnerable, endangered or critically endangered according to the IUCN Red List of Threatened Species ) from different major sources of threat (habitat loss/degradation, human harvesting, invasive species and pollution).
Location  Global, freshwater and marine.
Methods  We collated maximum body length data for 22,800 freshwater and marine fishes and compared body-size frequency distributions after controlling for phylogeny.
Results  We found that large-bodied marine fishes are under greater threat of global extinction, whereas both small- and large-bodied freshwater species are more likely to be at risk. Our results support the notion that commercial fishing activities disproportionately threaten large-bodied marine and freshwater species, whereas habitat degradation and loss threaten smaller-bodied marine fishes.
Main conclusions  Our study provides compelling evidence that global fish extinction risk does not universally scale with body size. Given the central role of body size for trophic position and the functioning of food webs, human activities may have strikingly different effects on community organization and food web structure in freshwater and marine systems.     

Short-range orientation in fish: How fish map space

One way in which fish can move around efficiently is to learn and remember a spatial map of their environment. This can be a relatively simple process where, for example, sequences of landmarks are learned. However, more complex spatial representations can be generated by integrating multiple pieces of information. In this review, we consider what types of information fish use to generate a spatial map; for instance, beacons (single landmarks) that signal a specific location, or learned geometric relationships between multiple landmarks that allow fish to guide their movements. Owing to the diversity of fish species and the broad range of environments that they inhabit, there is considerable diversity in the maps that they develop and the sensory systems that they use to detect spatial information. This chapter uses a series of examples to investigate the types of spatial information that fish encode, for instance, how they map three-dimensional space, how they make use of different sensory modalities, and where this information might be processed. We also highlight the versatility of short-range orientation in fish, and discuss a number of similarities between the mapping mechanisms used by fish and terrestrial vertebrates.     

Cleaner fish drives local fish diversity on coral reefs

Coral reefs are one of the most diverse habitats in the world, yet our understanding of the processes affecting their biodiversity is limited. At the local scale, cleaner fish are thought to have a disproportionate effect, in relation to their abundance and size, on the activity of many other fish species, but confirmation of this species' effect on local fish diversity has proved elusive. The cleaner fish Labroides dimidiatus has major effects on fish activity patterns and may indirectly affect fish demography through the removal of large numbers of parasites. Here we show that small reefs where L. dimidiatus had been experimentally excluded for 18 months had half the species diversity of fish and one-fourth the abundance of individuals. Only fish that move among reefs, however, were affected. These fish include large species that themselves can affect other reef organisms. In contrast, the distribution of resident fish was not affected by cleaner fish. Thus, many fish appear to choose reefs based on the presence of cleaner fish. Our findings indicate that a single small and not very abundant fish has a strong influence on the movement patterns, habitat choice, activity, and local diversity and abundance of a wide variety of reef fish species.     

Cloning of fish enzymes and other fish protein genes

Fish metabolism needs special enzymes that have maximum activity at very different conditions than their mammalian counterparts. Due to the differences in activity, these enzymes, especially cold-adapted proteases, could be used advantageously for the production of some foods. In addition to the enzymes, this review describes some other unique fish polypeptides such as antifreeze proteins, fluorescent proteins, antitumor peptides, antibiotics, and hormones, that have already been cloned and used in food processing, genetic engineering, medicine, and aquaculture. Recombinant DNA technology, which allows these biological molecules to be cloned and overexpressed in microorganisms is also described, highlighting innovative applications. The expected impact of cloning fish proteins in different fields of technology is discussed.     

Magnetoreception in fish

Magnetoreception is the ability of organisms to perceive magnetic fields in the surrounding environment and changes in its properties such as field direction, intensity and gradient, where the effect on organisms can manifest as an array of reactions. As the magnetic sense is found in many taxa, both evolutionarily young and old, it can be assumed that magnetoreception came into existence as one of the first sensory systems. Many studies on the effect of magnetic fields on fishes have considered both fishes that migrate for long distances and those that are more or less sedentary. Research has focused on tracing the perception of the geomagnetic field by fishes and understanding magnetic fields that are smaller and larger than the ambient Earth's geomagnetic field. The question of the effect of magnetic fields of values higher than the Earth's is gaining importance with the increasing effect of anthropogenic magnetic and electromagnetic fields in aquatic ecosystems. This review draws together the results of studies on the effect and reception of natural and human-generated magnetic fields on fishes at various stages of ontogeny, chronologically arranged from gametes, through embryonic development, embryonic and larval motor function, directional reactions of embryos and larvae, orientation of fishes, to the mechanisms of magnetic field reception. The present state of knowledge indicates a common nature of effect on various ontogenetic stages of fishes. However, understanding of the mechanisms of magnetic sense in fishes and its relevance for ecological outcomes highlights that further progress requires more detailed research.     

Choosy reef fish select cleaner fish that provide high-quality service

Reef fish that actively visit cleaner fish to have parasites and dead or infected tissue removed face two potential problems: they might have to wait while cleaners inspect other clients, and cleaners might feed on healthy body tissue, a behaviour that is referred to as cheating. Individuals of some ‘client’ species have large home ranges, which cover several cleaning stations, while others have small territories or home ranges with access to only one cleaning station. The former can thus choose between cleaners, while the latter cannot. We investigated whether clients with large home ranges change cleaning partners to outplay cleaners against each other to achieve (1) priority of access over clients with no choice at cleaning stations and (2) control over cheating by cleaners. We followed individuals of longnosed parrotfish, Hipposcarus harid, for up to 120 min in their natural environment and noted their interactions with cleaner wrasses, Labroides dimidiatus. Individuals were likely to return to the same cleaning station if the previous interaction had ended without conflict but changed cleaners for the next inspection if they had been either cheated or ignored, at least if the time between two consecutive visits was short. The overall attractiveness of a cleaning station seemed to be largely independent of service quality, which appeared to be similar at all stations. This is the first empirical evidence that the option to change partners is used as a control mechanism to stabilize cooperative behaviour.     

Transgenic fish.

A range of transgenic animal species have been generated using DNA microinjection, and application of this technique to fish is now showing some degree of success. Studies to optimize microinjection techniques specifically for use with fish, and to investigate possible alternative methods for mass culture, should lead to the commercial production of transgenic fish able to transmit desirable characteristics, such as enhanced growth or disease resistance, to their progeny.