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.     

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.     

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.     

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     

Presence of the fish pathogen Vibrio salmonicida in fish farm sediments

The persistence of the fish pathogen Vibrio salmonicida in fish farm sediments was studied by use of fluorescent-antibody techniques. The specificities of the monoclonal antibodies and polyclonal rabbit serum used in the study were tested against a number of Vibrio strains, including 4 isolates from intestinal tracts of healthy fish and 98 isolates from sediments. V. salmonicida was detected in sediment samples from diseased farms several months after an outbreak of the disease. The bacterium was also detected in a sediment sample from a disease-free fish farm. No V. salmonicida could be detected in sediments not influenced by fish farming. The number of positive samples was generally higher with application of rabbit serum as opposed to use of monoclonal antibodies, indicating that the rabbit serum may cross-react with other bacteria.     

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.     

Long-term cleaner fish presence affects growth of a coral reef fish

Cleaning behaviour is considered to be a classical example of mutualism. However, no studies, to our knowledge, have measured the benefits to clients in terms of growth. In the longest experimental study of its kind, over an 8 year period, cleaner fish Labroides dimidiatus were consistently removed from seven patch reefs (61-285 m(2)) and left undisturbed on nine control reefs, and the growth and parasite load of the damselfish Pomacentrus moluccensis determined. After 8 years, growth was reduced and parasitic copepod abundance was higher on fish from removal reefs compared with controls, but only in larger individuals. Behavioural observations revealed that P. moluccensis cleaned by L. dimidiatus were 27 per cent larger than nearby conspecifics. The selective cleaning by L. dimidiatus probably explains why only larger P. moluccensis individuals benefited from cleaning. This is the first demonstration, to our knowledge, that cleaners affect the growth rate of client individuals; a greater size for a given age should result in increased fecundity at a given time. The effect of the removal of so few small fish on the size of another fish species is unprecedented on coral reefs.     

Seasonality and heterogeneity of live fish movements in Scottish fish farms

Movement of live animals is a key contributor to disease spread. Farmed Atlantic salmon Salmo salar, rainbow trout Onchorynchus mykiss and brown/sea trout Salmo trutta are initially raised in freshwater (FW) farms; all the salmon and some of the trout are subsequently moved to seawater (SW) farms. Frequently, fish are moved between farms during their FW stage and sometimes during their SW stage. Seasonality and differences in contact patterns across production phases have been shown to influence the course of an epidemic in livestock; however, these parameters have not been included in previous network models studying disease transmission in salmonids. In Scotland, farmers are required to register fish movements onto and off their farms; these records were used in the present study to investigate seasonality and heterogeneity of movements for each production phase separately for farmed salmon, rainbow trout and brown/sea trout. Salmon FW-FW and FW-SW movements showed a higher degree of heterogeneity in number of contacts and different seasonal patterns compared with SW-SW movements. FW-FW movements peaked from May to July and FW-SW movements peaked from March to April and from October to November. Salmon SW-SW movements occurred more consistently over the year and showed fewer connections and number of repeated connections between farms. Therefore, the salmon SW-SW network might be treated as homogeneous regarding the number of connections between farms and without seasonality. However, seasonality and production phase should be included in simulation models concerning FW-FW and FW-SW movements specifically. The number of rainbow trout FW-FW and brown/sea trout FW-FW movements were different from random. However, movements from other production phases were too low to discern a seasonal pattern or differences in contact pattern.     

Gymnotiform fish: an important component of Amazonian fioodplain fish communities

Estimates of the density, biomass and species diversity of fish from floating meadow and flooded forest habitats suggest that gymnotiform fish constitute an important component of Amazonian flood plain fish faunas. Electric eels, Electrophorus electricus are unexpectedly abundant within Varzea forest.     

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.