The influence of status and the social environment on energy stores in a social fish

This study explores how muscle and liver energy stores are linked with social status and the social environment in Neolamprologus pulcher, a cooperatively breeding fish that lives in colonies comprised of up to 200 distinct social groups. Subordinate muscle energy stores were positively correlated with the number of neighbouring social groups in the colony, but this pattern was not observed in dominant N. pulcher. Furthermore, liver energy stores were smaller in dominants living at the edge of the colony compared with those living in the colony centre, with no differences among subordinates in liver energy stores. Subordinate N. pulcher may build up large energy stores in the muscles to fuel rapid growth after dispersal, which could occur more frequently in high‐density environments. Dominant N. pulcher may use the more easily mobilized energy stores in the liver to fuel daily activities, which could be more energetically demanding on the edge of the colony as a result of the increased predation defence needed on the edge. Overall, this study demonstrates that both subordinate and dominant physiology in N. pulcher varies with characteristics of the social environment. Furthermore, dominant and subordinate energy storage strategies appear to differ due to status‐dependent variation in daily activities and variation in the need to prepare for future reproductive or dispersal opportunities.     

Parasitic infections in freshwater ornamental fish in Sri Lanka

A total of 1520 ornamental fish of 13 species from 26 export farms in Sri Lanka were collected between October 1999 and March 2000 and examined for parasites. Fish species examined were guppy Poecilia reticulata, goldfish Carassius auratus, platy Xiphophorus maculatus, molly Poecilia sphenops, angel Pterophyllum scalare, swordtail Xiphophorus helleri, tetras Hyphessobrycon species, barbs Capeota and Puntius spp., gourami Colisa sp., carp Cyprinus carpio, fighters Betta spelendens and others (Brachydanio and Astronotus spp.). Nine species of monogenean trematodes (Dactylogyrus extensus, Dactylogyrus cf. extensus, D. vastator, Dactylogyrus cf. vastator Dactylogyrus spp., Gyrodactylus turnbulli, G. katherineri, Gyrodactylus cf. katherineri, Gyrodactylus spp.), 7 protozoan species (Trichodina nigra, Trichodina spp., Tetrahymena corlissi, T. pyriformis, Ichthyophthirius multifiliis, Ichthyobodo necator, Piscinoodinium spp.), 3 species of copepod arthropods (Lernaea cyprinacea, Ergasilus ceylonensis, Argulus foliaceus), 1 metacercarial stage of a digenean trematode (Centrocestus spp.) and 1 nematode (Capillaria spp.) were identified. Parasites were found in fish from 23 of the 26 farms with an overall prevalence of parasitism in 45.3% of fish. The variation in farm prevalence among different parasites was significant (p < 0.01). Fish infection rates with monogenean trematodes, protozoans, copepod crustaceans, digenean trematodes and nematodes were 28.3, 18.4, 4.8, 0.8 and 0.4%, respectively. In all, 50 out of 590 (50/590) guppies were infected with Tetrahymena, compared with 13/930 for all other species, which is a statistically significant result (p < 0.01). Similarly, 13/44 and 18/44 carp were infected with Argulus foliaceus and Lernaea cyprinacea, compared with 7/1476 and 15/1476, respectively, for all other species combined (p < 0.01). Capillaria spp. was found only in guppies (4/590) and angel fish (3/92) while Centrocestus spp. was found in goldfish (12/153) only.     

Parasitic crustaceans as vectors of viruses, with an emphasis on three penaeid viruses

Parasitic crustaceans serve as both hosts and vectors of viruses as well as of parasites and other microbial pathogenic agents. Few of the presumably numerous associations are known, but many can be anticipated. Recently, branchiurans and gnathiid isopods have been documented to host helminths and blood parasites. Because the agents can be observed readily with a microscope, these are better recognized than are the smaller viral, bacterial, and fungal agents. Some agents are harmful to the host of the crustacean parasite and others are not. Viruses probably fit both these categories, since viruses that do not appear pathogenic are often seen in ultrastructural images from a range of invertebrate hosts, including crustaceans. Some viruses have been implicated in causing disease in the host, at least under appropriate conditions. For example, lymphocystis virus may possibly be transmitted to the dermis of its fish hosts by copepods and to the visceral organs by a cymothoid isopod. Similarly, argulid branchiurans seem to transmit the viral agent of spring viremia of carp as well as carp pox, and copepods have been implicated in transmitting infectious hematopoietic necrosis, infectious salmon anemia, and infectious pancreatic necrosis to salmon. Other viruses can be vectored to their hosts through an additional animal. We exposed three viruses, Taura syndrome virus (TSV), white spot syndrome virus (WSSV), and yellowhead virus (YHV), all of which cause mortalities in wild and cultured penaeid shrimps, to crustacean parasites on fish and crabs. Using real-time polymerase chain reaction analysis, we show that TSV in the cyclopoid copepod Ergasilus manicatus on the gill filaments of the Gulf killifish, Fundulus grandis, the acorn barnacle Chelonibia patula on the carapace of the blue crab, Callinectes sapidus, and gooseneck barnacle Octolasmis muelleri on the gills of C. sapidus, can replicate for at least 2 weeks and establish what should be an infective dose. This result was additionally supported by positive in situ hybridization reactions. All three parasites are the first known non-penaeid hosts in which replication occurs. The mean log copy number of WSSV also suggested that replication occurred in E. manicatus. The mean log copy number of YHV gradually decreased in all three parasites and both hosts over the 2-week period. The vector relationships indicate an additional potential means of transmitting and disseminating the disease-causing agents to the highly susceptible and economically valuable penaeid shrimp hosts.     

Parasitic versus nutritional regulation of natural fish populations

Although parasites are expected to affect their host's fitness, quantitative proof for impacts of parasitism on wild populations is hampered by confounding environmental factors, including dietary resource. Herein, we evaluate whether the physiological conditions of European perch (Perca fluviatilis) in three large peri‐alpine lakes (Geneva, Annecy, and Bourget) depend on (a) the nutritional status of the juvenile fish, as revealed by stable isotope and fatty acid compositions, (b) the prevalence of the tapeworm Triaenophorus nodulosus, a parasite transmitted to perch through copepod preys, or (c) interactive effects of both factors. At the scale of lake populations, the deficit in growth and fat storage of juvenile perch during their first summer coincides with a high parasite prevalence and also a low quality of dietary resource. Yet, at the individual level, parasites had no evident effect on the growth of the juvenile perch, while impacts on fat storage appeared only at the highest prevalence of the most infected lake. Fatty acid and stable isotope analyses of fish tissue do not reveal any impact of T. nodulosus on diet, physiology, and feeding behaviour of fish within lakes. Overall, we found a low impact of parasitism on the physiological condition and trophic status of juvenile perch at the end of their first summer. We find instead that juvenile perch growth and fat storage, both factors tied to their winter survival, are under strong nutritional constraints. However, the coinciding nutritional constraints and parasite prevalence of perch juveniles in these three lakes may result from the indirect effect of lake nutrient concentrations, which, as a major control of zooplankton communities, simultaneously regulate both the dietary quality of fish prey and the host–parasite encounter rates.     

Antibiotic resistance of Salmonella strains isolated from fish and crustaceans

A total of 240 Salmonella strains, 158 from 730 fish samples and 82 from 276 crustacean samples, obtained during a 2 year period, were examined for resistance to 10 antibiotics. More than 90% of the strains were resistant to bacitracin, penicillin and novobiocin. The least resistance was observed to chloramphenicol (6·7%) and nalidixic acid (12%). Multiple antibiotic resistance indexing of the strains showed that more than 95% originated from high risk sources of contamination such as poultry, swine, cattle and human environments where antibiotics are often used.     

Parasitic diseases of marine fish: epidemiological and sanitary considerations

Over recent decades, parasitic diseases have been increasingly considered a sanitary and economic threat to Mediterranean aquaculture. In order to monitor the distribution of parasites in cultured marine fish from Italy and study their pathogenic effects on the host, a three-year survey based on parasitological and histopathological exams was carried out on 2141 subjects from eleven fish species and coming from different farming systems (extensive, intensive inland farms, inshore floating cages, offshore floating cages and submersible cages). A number of parasitic species was detected, mostly in European sea bass (Dicentrarchus labrax), gilthead sea bream (Sparus aurata), mullets (Chelon labrosus, Mugil cephalus, Liza ramada) and sharpsnout sea bream (Diplodus puntazzo), with distribution patterns and prevalence values varying in relation to the farming system, in-season period and size category. The epidemiology and pathological effects of the parasites found during the survey are discussed.     

Intestinal flora and social relations in laboratory rats

This paper deals with the quantitative study of the social interaction in dyads of laboratory rats. Two kinds of dyads of Rattus norvegicus were observed: one which had the conventional rat intestinal flora (S.S.C.u.p.) and the other a micro-flora (J.L.T.) derived from feral rats, each member of the dyad having the same sex. Contact-seeking and sniffing behaviour were more frequent and lasted longer in J.L.T. rats than in S.S.C.u.p.     

Saltmarsh as habitat for fish and nektonic crustaceans: Challenges in sampling designs and methods

This is a review of research into the ecological role of saltmarsh as habitat used directly by fish and nektonic crustaceans such as shrimp (prawns) and portunid crabs. The quality of information about direct use of saltmarshes by nekton is poor, with even the most influential works suffering from obvious limitations. Attempts to generalize about nekton use of saltmarshes are hampered by sampling difficulties, poor sampling design, and inconsistent reporting of flooding regime and landscape structure. The difficulty in sampling nekton from shallow, vegetated marsh flats while inundated contributes to the fragmentary results of nekton work. A range of sampling methods have been described that vary in portability, size, amount of above-ground structure, escape rates of nekton, and expense; none has yet become standard. Poor experimental design in studies of saltmarsh nekton includes lack of replication, limited spatial scale, and lack of baseline data before management changes are made. Attempts to determine effects on commercial fisheries of losses in area or quality of saltmarsh by correlations between catch data and marsh loss should use active adaptive management. A second type of study, aimed at understanding how the saltmarsh is important to fisheries, can be tackled usefully at a smaller scale. To assist in the comparison of results from different studies, flooding regime should be reported as a proportion of time the marsh is submerged, and landscape structure as proportions of the marsh that are covered by intertidal flats, pools and drainage creeks. Flooding regime and landscape structure at the sites and at the time of sampling should then be put in the context of the typical pattern for the marsh under study.     

On the influence of fishes on the evolution of benthic crustaceans

Though the interweavement of trophic chains in marine ecosystems of the past cannot be reconstructed, as the abundance, nutrition, reproductive rates and other aspects of the biology of fossil species are not known, it is possible to correlate trends in the evolution of single groups of animals, in the presented case the Crustacea, with the influence of other evolving organisms. The evolution of carnivorous, buoyant, well swimming modern fishes probably induced profound changes in marine ecosystems and influenced the evolution of crustaceans. Indications for these interactions are a. the absence or rare occurrence of defenseless archaic crustaceans in habitats, which are populated by teleostean fishes and the survival of some of these forms in refuges like caves and subterranean waters, and b. the reduction of the pleon in the course of the mesozoic evolution of the Decapoda, which occurs parallel to the radiation of the Teleostei, namely in the period between the early Jurassic and the Tertiary. The shortening of the pleon is interreted as a consequence of the stepwise change from a hyperbenthic to a more benthic Iife-stJe and the abandonment of the caridoid escape reaction. Other adaptations are also construed as results from the selective pressure produced by predators. Extant crustaceans which are able to coexist with fishes, among the macrozoobenthos especially the Decapoda and Peracarida, have a variety of protective adaptations, which help to reduce predation.     

Immunolocalization of four antioxidant enzymes in digestive glands of mollusks and crustaceans and fish liver

The aim of this work was to determine the immunolocalization of the antioxidant enzymes catalase, Cu,Zn-superoxide dismutase (SOD), Mn-SOD, and glutathione peroxidase (GPX) in the bivalve mollusks Mytilus galloprovincialis and Crassostrea sp., the crab Carcinus maenas, and the teleostean fish Mugil cephalus. By immunoblotting, crossreactivity between antibodies and the corresponding proteins in the digestive gland/hepatopancreas of invertebrates and the fish liver was demonstrated. Immunohistochemical studies showed that the stomach epithelium was strongly immunostained for catalase in mollusks. In crabs, ducts showed stronger immunostaining than tubules and in mullet hepatocytes the reaction appeared in discrete granules corresponding to peroxisomes. With regard to Cu,Zn-SOD, the apex of the tubule cells in mussels and crabs was distinctly immunostained, whereas in oysters the reaction was more marked in ducts and in mullet liver a uniform diffuse cytoplasmic staining was found. Mn-SOD was strongly positive in mollusk and crab ducts and in mullet periportal hepatocytes. Finally, GPX was not detected in mussels while in oysters a slight reaction was noted in all cell types. In crabs, connective tissue cells and the apex of duct cells were immunostained, but in mullet liver only erythrocytes appeared reactive. Immunoelectron microscopy revealed that catalase was localized in peroxisomes with a dense labeling in fish and less intense labeling in invertebrates. Cu,Zn-SOD was mainly a cytosolic protein although additional positive subcellular sites (peroxisomes, nuclei) were also observed, while Mn-SOD was restricted to mitochondria. GPX was localized in the cytosol, nucleus, and lysosomes, occurring also in peroxisomes of the fish liver. The results presented here provide a basis for future application of the immunodetection techniques to study the possible differential induction of antioxidant enzymes in aquatic organisms subjected to oxidative stress as a result of exposure to environmental pollutants.     

Assortative interactions and social networks in fish

The mechanisms underpinning the structure of social networks in multiple fish populations were investigated. To our knowledge this is the first study to provide replication of social networks and therefore probably the first that allows general conclusions to be drawn. The social networks were all found to have a non-random structure and exhibited social cliquishness. A number of factors were observed to contribute to this structuring. Firstly, social network structure was influenced by body length and shoaling tendency, with individuals interacting more frequently with conspecifics of similar body length and shoaling tendency. Secondly, individuals with many social contacts were found to interact with each other more often than with other conspecifics, a phenomenon known as a positive degree correlation. Finally, repeated interactions between pairs of individuals occurred within the networks more often than expected by random interactions. The observed network structures will have ecological and evolutionary implications. For example, the occurrence of positive degree correlations suggests the possibility that pathogens and information (that are socially transmitted) could spread very fast within the populations. Furthermore, the occurrence of repeated interactions between pairs of individuals fulfils an important pre-requisite for the evolution of reciprocal altruism.