Toxin accumulation and feeding behaviour of the planktonic copepod Calanus finmarchicus exposed to the red-tide dinoflagellate Alexandrium excavatum

The planktonic copepod Calanus finmarchicus is a dominant member of the zooplankton community in the lower St. Lawrence Estuary in eastern Canada. Blooms of the toxic marine dinoflagellate Alexandrium excavatum which produces high cellular levels of paralytic shellfish poisoning (PSP) toxins, occur during the period of high C. finmarchicus production in summer in this region. To study the feeding behaviour of C. finmarchicus in the presence of Alexandrium spp., experiments were conducted in which female adult copepods collected from the St. Lawrence Estuary between May and September 1991 were exposed under controlled conditions to two toxic isolates of A. excavatum (Pr18b and Pr11f) from the estuary and to a non-toxic control (PLY 173) of a closely related species, A. tamarense isolated from the Tamar Estuary, Plymouth, U.K. Clearance rates on non-toxic A. tamarense cells averaged 5.5 ml ind^-1 h^-1 but were nearzero with either toxic isolate. When presented with a mixture of A. excavatum and the non-toxic diatom Thalassiosira weissflogii in varying proportions, C. finmarchicus fed upon the diatom but avoided the toxic dinoflagellate. Although feeding rates on A. excavatum were very low, toxin analysis by high-performance liquid chromatography with fluorescence detection (HPLC-FD) revealed that the PSP toxins were accumulated in copepods exposed to toxigenic dinoflagellates.The toxin composition in copepods was similar to that of the toxic dinoflagellate, but not necessarily identical, particularly after short-term (2-h) exposure, when relatively elevated levels of N-sulfocarbamoyl toxins were detected. The evidence suggests that C. finmarchicus ingests toxic dinoflagellate cells, either mistakenly or during exploratory bouts of feeding, and accumulates PSP toxins in its gut system and perhaps in other tissues.     

Direct estimation of natural mortality rates for littoral marine fishes using populational data from a marine reserve

 Visual censuses conducted in a marine reserve (Medas Islands) were used to estimate the natural mortality rates (M) for five common fish species in the NW Mediterranean Sea (Coris julis, Diplodus annularis, D. sargus, Serranus cabrilla and Symphodus roissali). Visual censuses of these same five species were also performed at three sites in unprotected areas of the coast where both commercial and sport fishing activity was normal. Censuses were conducted over a 3 year period. Estimates of M in the 3 years displayed scant seasonal or interannual variation, which may mean that the populations were in equilibrium during that period. The results of this study showed that the relationships between M and the growth parameters and maximum life span were unclear, and considerable caution is therefore recommended when using indirect methods of estimating M based on those parameters. For certain species the values of M were equal to or greater than the estimated total mortality in the exploited areas. The virtual absence of piscivorous predators in the unprotected area as a consequence of the high level of fishing in that area contrasts with the high abundance of such predators in the marine reserve. Since predation is the main contributor to M, estimated mortality in the unprotected areas is attributable nearly entirely to fishing. It is suggested that M may vary according to alterations taking place in conditions in the ecosystem inhabited by a species and thus that use of a value of M for a pristine population cannot be extrapolated to exploited areas. Received: 18 January 2000 / Accepted: 14 July 2000     

Exposure assessment for mercury from consumption of marine fish in Iran

Seven species of marine fish in the Persian Gulf and three species of marine fish in the Caspian Sea were collected from the local wholesale market in Mashhad, Iran. The mercury (Hg) concentration in muscle samples was determined by atomic absorption spectrophotometry. High total Hg concentration was found in Anchovy sprat (2.04 ± 1.23 µg g^?1) and Whitecheek shark (1.26 ± 1.85 µg g^?1) and the lowest content was detected in common carp (0.24 ± 0.24 µg g^?1) and Caspian salmon (0.25 ± 0.08 µg g^?1). The mean Hg content in all samples was 0.91 ± 1.07 µg g^?1. All samples of Persian Gulf and one sample of Caspian Sea had mean Hg concentration above 0.5 µg g^?1, the level established by joint FAO/WHO on Food Additives. Results showed that the estimated weekly intake of total Hg by a 60 kg adult is below the provisional tolerable weekly intakes recommended by joint FAO/WHO on Food Additives. For prevention of health risks, populations in Iran need to consume fish in moderate amounts.     

A re-evaluation of the diel feeding hypothesis for marine herbivorous fishes

We re-evaluated the "diel feeding hypothesis" by measuring diel variation in starch, protein, and floridoside in three algal "types" collected from a fringing coral reef at Lizard Island, Great Barrier Reef, Australia. Samples of two species of rhodophyte algae, Gracilaria arcuata and Acanthophora spicifera, and the turf assemblage from the territories of the herbivorous pomacentrid Stegastes nigricans were collected at four time periods through the day: 0630-0730, 1000-1100, 1330-1430, and 1630-1730 hours. We also measured the ability of several species of marine fish (the herbivores Acanthurus nigricans, A. lineatus, A. olivaceus, and Parma alboscapularis and the detritivore Ctenochaetus striatus) to hydrolyse floridoside by estimating !-galactosidase activity in tissue from the anterior intestine. We detected no diel pattern in protein content of the algae but found a significant steady increase in starch content throughout the day. Floridoside content increased in the morning and decreased in the afternoon, a pattern that may be driven by midday photoinhibition of the algae. All the fishes tested could utilise floridoside. Our results support the diel feeding hypothesis. Although floridoside content decreased in the afternoon, our results suggest floridoside was used during the day by the algae to synthesise starch. Thus the algae increased in nutritional value until photoinhibition occurred at midday then subsequently maintained their nutritional value during the afternoon. This pattern of algal nutrients increasing to a midday peak and remaining relatively constant throughout the afternoon correlates well with the diel feeding pattern in many species of marine herbivorous fish.     

Effects of fish feeding by snorkellers on the density and size distribution of fishes in a Mediterranean marine protected area

Although there is a great deal of evidence to show that supplementary feeding by humans in terrestrial environments causes pronounced changes in the distribution and behaviour of wild animals, at present very little is known about the potential for such effects on marine fish. This study evaluated the consequences of feeding by snorkellers on fish assemblages in the no-take area of the Ustica Island marine protected area (MPA; western Mediterranean) by (1) determining if reef fish assemblage structure is affected in space and time by tourists feeding the fish; (2) assessing the effects of feeding on the abundance of the most common fish species; and (3) assessing the effects of feeding on the size structure of the two most numerically dominant ones. In particular, we hypothesised that both the abundance and the size structure of some fish species would increase at the study site following supplementary feeding, since the additional food provided by humans would make the site more appealing to them. Fish feeding influenced the fish assemblages within the Ustica MPA, and significant spatio-temporal changes occurred. While fish feeding appeared to have no effect on the ornate wrasse Thalassoma pavo, there was a noticeable increase in the number of Oblada melanura and Epinephelus marginatus in the impacted location after feeding. It is very likely that aggregations of fishes that evolve as a result of fish feeding by the public may have negative effects on local populations of fishes and invertebrates that make up their prey. Recreational use of coastal areas and MPAs is increasing elsewhere, making fish feeding a generalised human activity. Accurate information about its effect on the fish assemblage is essential to make responsible management decisions.Communicated by R. Cattaneo-Vietti, Genova     

Feeding and absorption of the toxic dinoflagellate Alexandrium tamarense by two marine bivalves from the South China Sea

Paralytic shellfish poisoning (PSP) toxins can be accumulated by bivalves through the feeding process; therefore, knowledge on feeding and the assimilation of PSP-toxin-containing algae is critical to understand the kinetics of PSP toxins in these bivalves. In the South China Sea, it has been documented that the scallop Chlamys nobilis has a much higher PSP toxin burden than the clam Ruditapes philippinarum. Experiments were therefore carried out to assess whether the difference in toxin burden between these two species of bivalves was due to differences in feeding and absorption. In a mixed diet of Alexandrium tamarense (a PSP-toxin-producing dinoflagellate) and Thalassiosira pseudonana (a non-toxic diatom), the maximum clearance and filtration rates were about two times higher in the scallop C. nobilis than in the clam R. philippinarum. Furthermore, the clams produced pseudofeces at a lower cell density than the scallops. However, we found that the clams were unable to selectively exclude the toxic dinoflagellates by pseudofeces production. The scallop C. nobilis also possessed a greater ability to assimilate A. tamarense with a comparable carbon absorption efficiency to the diatom T. pseudonana. In contrast, the carbon absorption in the clam R. philippinarum was lower when feeding on A. tamarense than on the diatom. In general, the absorption efficiency decreased with increasing concentration of A. tamarense. Thus, it is likely that the higher PSP toxin levels in the scallops compared with clams can be partly explained by differences in their feeding and absorption behavior. Other processes, especially the biotransformation and biokinetics of PSP toxins, may also play a significant role in defining the inter-species differences in PSP body burden in marine bivalves.     

Effect of neem extract against the bacteria isolated from marine fish

Marine ornamental fishes are exceedingly valuable due to their high demand in domestic and international markets. There is a growing global interest to rear the fishes in captivity. But problem due to bacteria and fungi are the major hitch in captive condition. Since, the use of antibiotics is banned, an attempt was made to ascertain in vitro assay of the neem leaves extract against the bacterial pathogens isolated from infected fishes. Bacterial strains isolated from infected regions of the clown fishes Amphiprion sebae and A. ocellaris were identified as Aeromonas hydrophila, Enterobacter sp., E. coli, Pseudomonas aeruginosa, Proteus sp., Streptococcus sp., Vibrio cholerae, V. alginolyticus, V. parahaemolyticus and Yersinia enterocolitica. Ethanol and methanol extracts were highly inhibitory to the bacterial isolates when compared to other solvents. Ethanol extracts exhibited low minimum inhibitory concentration (75-250 microg ml(-1)) as compared to other extracts. The present finding revealed that the neem leaf extract significantly reduces the bacterial pathogens and their infection in marine ornamental fishes.     

A new growth model for fishes and the estimation of optimum age of fish populations

Evidence is presented that a simple power equation of the formX _t –X _m =±b(|tࢤt _m|)^B can describe growth in length and weight of fishes, whereX _t denotes fish length or weight at aget, X _m is length or weight (L _m orW _m ) at a reference aget _m , andb andB are parameters to be estimated by the least squares. The optimum age of fish populations (t _y ) may be estimated by the equationMW _m /b=±y ^B (B/y-M) whereM denotes natural mortality and wherey=t _y -t _m .     

Influence of bacteria on growth and hemolysin production by the marine dinoflagellate Amphidinium carterae

The effect of various bacteria on the growth of and hemolysin production by Amphidinium carterae was studied. The algal culture had an indigenous bacterial flora of Moraxella and Pseudomonas and these could not be eliminated by treatment with bactericidal antibiotics like gentamicin. Various bacteria like Micrococcus, Aeromonas, Vibrio, and Moraxella-like bacteria were added to A. carterae cultures to study their effect on growth and hemolysin production. Micrococcus and Aeromonas were found to improve the growth marginally. Hemolysin titres were considerably higher in A. carterae cultures supplemented with bacteria. Received: 27 May 1997 / Accepted: 22 July 1997     

Bacterial chitinase in the stomachs of marine fishes from Yaquina Bay,Oregon, USA

The occurrence of chitinase in the stomach contents of Enophrys bison and Platichthys stellatus was investigated. The highest chitinase activity and the greatest percentage of chitinoclastic bacteria in relation to the total bacterial flora were associated with fish whose stomach content was composed primarily of chitinous animals. Stomach contents lacking visible chitin possessed low or no detectable levels of chitinase activity and few chitinoclastic bacteria. Juvenile E. bison treated with chloramphenicol to remove their indigenous bacterial flora had no detectable level of chitinase in their stomach contents while non-treated juveniles showed inducible chitinase activity, indicating the bacterial origin for the chitinase.Published as Technical Paper No. 4435, Oregon Agricultural Experiment Station. This research was supported by NIH training grant 5TO1 GM-00704 and NSF grant DES73-06611 AO2.     

Clostridia dominate 16S rRNA gene libraries prepared from the hindgut of temperate marine herbivorous fishes

Bacterial diversity in the microbial communities of posterior gut sections of three temperate marine herbivorous fish species from New Zealand was characterised using Amplified Ribosomal DNA Restriction Analysis, and 16S rRNA gene amplification and sequencing methods. The fish were collected in 1999–2000 in the Hauraki Gulf, New Zealand (35°54’–36°24’S, 174°48’–175°25’E). The gastrointestinal bacterial communities of Kyphosus sydneyanus (Günther, 1886) (F. Kyphosidae), Odax pullus (Forster in Bloch and Schneider, 1801) (F. Labridae) and Aplodactylus arctidens Richardson, 1839 (F. Aplodactylidae) were dominated by five clades of bacteria, four of which belong to recognized clostridial clusters. The clone libraries of K. sydneyanus and O. pullus contained sequences from most of these clades, but were dominated by members of clostridial clusters XI and XIVa, respectively. The clone library of A. arctidens was dominated by members of clostridial cluster XIVb and an unassigned cluster containing Eubacterium desmolans and Papillibacter cinnaminovorans. The finding that strains of Firmicutes dominated the gastrointestinal microbial communities of all three fish species is consistent with the results of similar studies on terrestrial vertebrate herbivores. This work thus contributes to the view that gastrointestinal symbionts in some marine herbivorous fishes may play a similar role to those in terrestrial vertebrate herbivores studied to date.     

Effects of nutrient limitation on toxin production and composition in the marine dinoflagellate Protogonyaulax tamarensis

Toxin production was measured by high pressure liquid chromatography (HPLC) when the marine dinoflagellate Protogonyaulax tamarensis (NEPCC 255) was grown under nitrogen or phosphorus limitation. The major toxins found in P. tamarensis (255) consisted of (N21-SO ₃ ^- )STX (11%), (N21-SO ₃ ^- )NeoSTX (44%), and [(N21-SO ₃ ^- )GTX₂ plus (N21-SO ₃ ^- )GTX₃] (20%). Total toxin content on a per cell basis was high for cultures in log phase (30 to 40 fmol cell^-1) and then decreased to ca 20 fmol cell^-1 as the cultures entered stationary phase. There was a gradual decrease in the toxin content per cell during nitrogen-limited stationary phase to ca 3 fmol cell^-1 or less. Phosphorus-limited cultures showed a markedly different response than nitrogen-limited cultures. Toxin content in P-limited cells dramatically increased at the start of stationary phase, reaching levels 3 to 4 times that observed in control and nitrogen-limited cultures. These results cannot be explained by changes in the average cell volume. Eventhough dramatic effects on the total toxin concentration were observed in response to nutrient limitation (N or P), the toxin composition (on a percent basis) remained constant. This suggests that the individual toxin composition of a given isolate is a fixed genetic trait and not a transient response to changing environmental factors.     

Comparative studies on the metabolism of shallow-water and deep-sea marine fishes. I. White-muscle metabolism in shallow-water fishes

Maximal rates of oxygen consumption in vitro have been measured under standardized conditions at three test temperatures (5°, 15°, and 25°C) on minced preparations of white muscle from 39 species of shallow-water marine teleost fishes. These fishes came from four different geographic areas, two with cool average water-temperatures (near 15°C: coastal southern California, Galápagos Islands) and two with warm average water-temperatures (near 25°C: Hawaiian Islands; Bermuda). The group includes species covering much of the range of variation to be found among the teleosts with respect to five additional variables: phylogenetic position, type of environment, body weight, activity level, and growth stage. The purpose of the work is to provide part of a base line of tissue-metabolism data on shallow-water fishes for comparison with similar results from deep-sea species. Major conclusions from statistical analyses of the results are: four groups of shapes of oxygen-uptake rate versus temperature curves exist: normal, flat, dipped and peaked. Over 50% of curves are normal. Intra-group differences, contributing significantly to the total variance of the results at given test temperatures, are: cool versus warm average environmental temperatures primarily for epipelagic species; epipelagic versus non-epipelagic environments; very active species versus all others; juvenile stages versus adults. In each case, the subgroup first mentioned shows higher muscle oxygen-uptake rates than the other subgroup. Variables not contributing significantly to the total variance are phylogenetic position and body weight. Physiological and ecological implications of these results are discussed.     

Development and characterization of complex particles for delivery of amino acids to early marine fish larvae

Complex particles (CP), zein microbound particles and lipid-spray beads (LSB) were prepared and their performances were compared for delivering glycine and a mixture of free amino acids (FAA; alanine, glycine, leucine, serine and tyrosine) to early fish larvae. Measures of performances of microparticles included inclusion, encapsulation, retention and delivery efficiencies in addition to T50 (time to 50% retention) values. CP were prepared containing LSB and a defined dietary mixture that were bound together with zein. CP had significantly higher retention and delivery efficiencies for FAA compared to those of zein microbound particles. Free LSB had higher retention efficiencies for particulate glycine compared with CP, possibly due to differences in suspension characteristics. Free LSB clumped and floated when suspended in water, negatively affecting their acceptability by fish larvae; therefore, LSB should be incorporated into CP for more effective delivery of amino acids. There was a significant inverse correlation between retention efficiencies and solubilities of FAA encapsulated in CP. After 1 h of aqueous suspension, highest retention (44%) and delivery efficiencies (20.3 mg tyrosine g^–1 particle) were achieved with tyrosine. T50 values indicated 50% of the initial tyrosine in CP was still available after 36.7 min of suspension in water. Furthermore, CP can deliver FAA to marine fish larvae based on the results of feeding studies in which CP were digested by 3-day-old clownfish larvae; therefore, this particle type could be a valuable tool in studies of larval fish nutrition.Communicated by R.J. Thompson, St. Johns     

Comparative studies on the metabolism of shallow-water and deep-sea marine fishes. II. Red-muscle metabolism in shallow-water fishes

Maximal rates of oxygen consumption in vitro have been measured under standardized conditions at three test temperatures (5°, 15°, 25°C) on minced preparations of red muscle from 10 species of shallow-water marine teleost fishes. These fishes came from three different geographic areas, two with cool average water temperatures (near 15°C: coastal southern California, Galápagos Islands) and one with warm average water temperatures (near 25°C: Hawaiian Islands). The group is made up of post-juvenile or adult epipelagic fishes, which are moderately or very active in terms of their locomotor activities. A large part of the range of phylogenetic diversity among the teleosts is represented, as is the body weight range from a few grams to several kilograms. The purpose of the work is to provide part of a set of tissue-metabolism data on shallow-water fishes for future comparison with similar results from deep-sea species. Of 8 complete curves for oxygen uptake rate versus temperature (R-T curves), 6 are normal in shape (Q₁₀1.5), 1 is normal but with a low Q₁₀, and 1 is partly flat, partly normal. The differences between the species in terms of both absolute positions and slopes of the R-T curves are not related in any consistent way to any of the three testable variables: phylogenetic position, long-term adaptation temperature, and body size. The red muscles of a variety of adult epipelagic fishes, at ecologically realistic temperatures, are shown to be exceptions to the general rule that tissues of ectothermous lower vertebrates have lower metabolic rates than comparable tissues of non-torpid endothermous higher vertebrates. This circumstance probably is a major factor in the great capacities for sustained high-speed swimming shown by most epipelagic fishes. Other physiological and ecological implications of the results are discussed.     

Distribution and abundance of marine fish larvae in relation to effluent plumes from sewage outfalls and depth of water

Fish larvae were sampled in and below three separate sewage plumes associated with the cliff-face (shoreline) outfalls at North Head, Bondi and Malabar, and at three control (non-plume) sites located>8 km away from the sewage outfalls, at Long Reef, Port Hacking and Marley Beach, in nearshore waters off Sydney, south-eastern Australia. Samples were collected at the surface and at 20 m depth during three periods: December 1989, April/May 1990 and August/September 1990. In December 1989, a greater number of taxa were caught at both depths at the plume sites compared to the control sites, but this did not occur during the other two sampling periods. Similarly, in April/May 1990, greater numbers of the clupeid Hyperlophus vittatus but fewer anthiines were caught at both depths near the outfalls (plume sites). Myctophids were more numerous in surface samples, but not at 20 m, at the plume sites in both April/May and August/September 1990, whereas in April/May 1990, labrids and anguilliformes were less abundant at 20 m at the plume sites compared to the control sites. These differences in the numbers of fish larvae caught may have been an effect of the effluent plumes, but these results were only correlative. The results most probably reflect spatial heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney. There were striking differences, however, in the number of fish larvae caught at the surface and at 20 m, and among sampling periods, but these differences were similar across all sites. Of the 46 taxa considered common, 33 occurred in greater numbers at 20 m than at the surface, whereas only 8 taxa were caught in greater numbers at the surface. The composition of the fish larvae also differed markedly among sampling periods; few taxa were common to all three sampling periods. Greater numbers of fish larvae were caught in April/May and August/September 1990 than in December 1989, particularly at 20 m depth. The data highlight the large spatial and temporal heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney and the difficulty of identifying effects that are solely due to sewage plumes.     

Organic and caloric levels of fish feces relative to its consumption by coprophagous reef fishes

Levels of protein, lipid, carbohydrate, ash, and calcium in the rectal contents of a species representative of each of four trophic groups of coral reef fishes were determined. These levels and the estimated caloric levels were related to the degree to which the feces of each species were eaten by species of coprophagous fishes and to the potential nutritional value of their non-fecal foods. The potential nutritional value of feces (based on estimated caloric content), protein and lipid levels were positively correlated with the percentage of feces eaten by coprophagous fishes. Levels of calcium and ash were negatively correlated with the percentage eaten. Fecal carbohydrate level was not correlated with the degree of ingestion. Food values of these feces were at least equal to those of non-fecal foods (i.e. zooplankton, coral tissue, algae, etc.) of the coprophages. Feces produced by the coprophagous species had even lower potential food value.     

Effects of sex change on the implications of marine reserves for fisheries

Marine reserves have become widely used in biodiversity conservation and are increasingly proposed as fisheries management tools. Previous modeling studies have found that reserves may increase or decrease yields, depending on local environmental conditions and on the specific life-history traits of the fishery species. Sex-changing (female-to-male) fish are targets of some of the most important commercial and recreational fisheries in the world. The potential for disproportionate removal of the larger, older sex of such species requires new theory to facilitate our understanding of how reserves will affect the yields of surrounding fisheries, relative to fishes with separate sexes. We investigated this question by modeling the effects of marine reserves on a non-sex-changing and a sex-changing population. We used demographic parameter estimates for the common coral trout as a baseline, and we conducted extensive sensitivity analyses to determine how sustainable yields of sex-changing species are likely to be affected by reserves across a broad range of life-history parameters. Our findings indicate that fisheries for sex-changing species are unlikely to receive the same yield-enhancing benefit that non-sex-changing fisheries enjoy from marine reserves, and that often reserves tend to reduce sustainable yields for a given overall population size. Specifically, the increased egg production and high fertilization success within reserves is more than offset by the reduced egg production and fertilization success in the fished areas, relative to a system in which fishing mortality is distributed more evenly over the entire system. A key reason for this appears to be that fertilization success is reduced, on average, when males are unevenly distributed among subpopulations, as is the case when reserves are present. These findings suggests that, for sex-changing populations, reserves are more suited to rebuilding overfished populations and sustaining fishery viability, rather than enhancing fishery yields. These results are robust over a range of sex-change regimes, stock-recruitment relationships, adult mortality rates, individual growth strategies, and fertilization-success functions. Our findings highlight the importance of considering the different contributions of males and females to population growth and fishery yields when evaluating the efficacy of marine reserves for enhancement of fished species.     

Comparison of herbivory in the closely-related marine fish genera Girella and Kyphosus

  Specimens of the nominally herbivorous, closely-related, fish genera Girella and Kyphosus were collected from Australian waters in 1994 and 1995. The diet of three Girella species (G. cyanea, G. elevata, and G. tricuspidata) consisted mainly of chlorophytes and rhodophytes, with an animal component of␣15.9 ± 4.2% in G. tricuspidata. The diet of four species of Kyphosus (K. bigibbus, K. cinerascens, K. sydneyanus, and K. vaigiensis) included phaeophytes, chlorophytes and rhodophytes, and almost no animal material. Concentration of total short-chain fatty acids in the posterior intestine was <11.4 mM in the Girella spp. and >39.2 mM in the Kyphosus spp. These results suggest that microbial fermentation plays a role in algal digestion in Kyphosus spp., but not in Girella spp. Girellids and kyphosids appear to function quite differently as herbivores. Girellids should be considered as omnivores that complement readily-available energy from algae with protein from invertebrates. Kyphosids appear to be strict herbivores that can derive adequate nutrition from algae poor in easily assimilable energy, through microbial fermentation in the hindgut. Received: 8 July 1996 / Accepted: 2 August 1996