Fish Carcasses Research Articles

Complexo zinco aminoácido em dietas práticas para a tilápia do Nilo (Oreochromis niloticus)

Commercial diets for fish culture are supplemented with an inorganic zinc sources. Zinc oxide (ZnO) is the most utilized Zn supplementation in Brazil. However, organic metal complexes may increase mineral absorption in the digestive tract. Based on this knowledge, the effects of a amino acid zinc complex (Zn-AA) upon growth performance and carcass composition of Nile tilapia, Oreochromis niloticus L., fingerlings, were compared to the ones observed for ZnO. Isoproteic and isoenergetic soybean meal/corn-based diets were offered to fish for 75 days, supplemented with 30, 90, 150 or 210mg Zn/kg, from ZnO or Zn-AA. Fish (1.79 ± 0.10g) were allocated in thirty six 250-L tanks, and fed ad libitum four times a day. Fish fed with ZnO-supplemented diets, regardless of the supplementation level, showed a significantly higher weight gain than the animals fed with Zn-AA-supplemented diets (P<0.05). Besides, food conversion and protein efficiency ratio of fish fed with ZnO were significantly better than the verified for fish fed with Zn-AA-supplemented diets. The proximal composition of fish carcasses was statistically similar (P>0.05) for different experimental treatments. The experiment showed that Zn-AA supplementation produced worse fish growth performance than ZnO.

Effects of dietary fish oil replacement on growth and carcass proximate composition of juvenile barramundi (Lates calcarifer )

An experiment was carried out to determine the effects of dietary fish oil replacement at an optimal level on the growth and carcass proximate composition of juvenile barramundi or sea bass (Lates calcarifer). Ten fish feeds were formulated to contain iso-ingredients with theoretically identical dietary lipid levels but with different sources of lipids (fish oil, soybean oil, canola oil and linseed oil) replacing dietary fish oil. Three hundred fish were equally divided into 30 70-L plastic tanks (three replicate tanks for each treatment). Fish were fed with experimental diets for 40 days within closed recirculating freshwater systems (70 L h−1, 28°C and 12L:12D). Growth, specific growth rate, food conversion ratio (FCR) and carcass proximate composition were determined. Dietary lipids significantly affected (P<0.05) the growth of the fish. Good growth and low FCR were observed in all treatments. Therefore, fish oils can be partially replaced by vegetable oils to reduce the feed cost. There were no significant differences (P>0.05) in lipid, moisture and protein content in fish carcasses among the group. However, juvenile barramundi showed increasing lipid and moisture content in muscle, whereas decreasing protein content when compared to the initial fish.

Mercury accumulation and loss by necrophageous calliphoridae larvae (diptera)

Fish represent the dominant methylmercury (CH 3 Hg) pool in aquatic systems and CH 3 Hg released from carcasses after fish death could constitute a significant flux to the environment. Necrophageous invertebrates play an important role in this Hg recycling. Necrophageous calliphorid fly larvae (Diptera) are known to consume beached carcasses. In this study, we report that the Hg these flies accumulate from fish carcasses is retained in their pupal stage but is eliminated by the adult following emergence. Thus calliphorids possess an efficient mechanism for excreting the Hg that they accumulate from carcasses.

Spring growth of caddisflies (Limnephilidae : Trichoptera) in response to marine-derived nutrients and food type in a Southeast Alaskan stream

The short-term stimulation of production, due to marine-derived nutrients (MDN) from spawning salmon, is well documented for certain trophic levels in stream communities (e.g., algae and insect biomass). The effect of these nutrients on the stream ecosystem as a whole, however, remains unclear especially later in the year. Trichopterans have been shown to feed on salmon and other fish carcasses and there is evidence for greater growth rates in the presence of salmon tissue. To address the question of long-term MDN subsidy on trichopterans, we investigated the growth of three limnephilid caddisflies in the spring in the Harris River on Prince of Wales Island, Southeast Alaska. The Harris River has a natural waterfall barrier to salmon and receives large runs of pink (O. gorbuscha) and chum (O. keta) salmon each fall. We selected two shredding caddisflies (Onocosmoecus unicolor) and (Psychoglypha spp.) and one facultative scraper, (Dicosmoecus atripes) for our study. We had two objectives : 1) compare the spring growth of larval caddisflies in a stream section that receives a large autumn run of salmon with their growth in a stream section that is blocked from receiving salmon (due to an impassable waterfall), and 2) compare the growth of shredders with that of a facultative scraper when provided either leaves or biofilm on rocks as food. Insects were placed in growth boxes in May 2001 with either conditioned alder leaves or stream rocks as food sources. The boxes were placed along with temperature loggers in both the salmon (below the waterfall) and non-salmon (above the waterfall) reaches. The boxes were removed 40 days later. In-stream samples were taken of each caddisfly initially and at the end of the experiment to establish in-stream growth versus growth in the boxes. All larvae were coaxed from their cases, measured for total wet length, dried and weighed. Only D. atripes and Psychoglypha spp. were growing during our experiment and both showed very high relative growth rates in the Harris River. Psychoglypha spp. and O. unicolor were both significantly larger in the leaf boxes and D. atripes was significantly larger in the rock boxes. Both D. atripes and Psychoglypha spp. had significantly greater relative growth rates between food types (on biofilm on rocks and leaves respectively). These results support the notion that D. atripes are most likely facultative scrapers at least in their first year of growth. None of these caddisflies showed differences in their final mean weights or relative growth rates between stream sections, suggesting no effect of MDN on their spring growth in the Harris River. Further research on caddisfly communities in the fall and winter will help clarify if MDN has an influence on the abundance and life history of these species closer to the salmon run. This study questions the long-term influence of MDN on stream communities, particularly those populations that do most of their production in the spring, months after salmon carcasses are no longer visible.

Growth, Feed Utilization And Carcass Composition In Rainbow Trout Fed Diets With A Similar Digestible Energy Content And Different Carbohydrate Levels

Three diets including 13.2%, 22% or 30.5% carbohydrates as extruded wheat meal were fed to rainbow trout, Oncorhynchus mykiss (initial weight 34.8 g), for twelve weeks to investigate their influence on growth, protein and energy utilization and carcass composition. Daily feeding rates were 1.76, 2.05 or 2.17 g feed per 100 g body weight for the three diets, respectively, so as to reach a daily allowance of about 35.5 kJ digestible energy per 100 g body weight. No significant differences (p&gt;0.05) in final mean weight or specific growth rate were observed between the treatments. Feed efficiency was negatively correlated to the dietary carbohydrate level. Utilized digestible protein and energy per kg growth were 365, 348, 358 g and 15.4, 15.9, 17.0 MJ, respectively, for the three diets. Apparent net protein and energy utilization of the groups fed a medium or high carbohydrate level were higher than those of the low carbohydrate group. Analysis of fish carcasses at the end of the trial revealed no significant (p&gt;0.05) variations attrib- utable to the carbohydrate level.

Evaluation of Experimental and Practical Diets for Walleye Stizostedion vitreum

AbstractCulture of walleye Sfizostedion vitreum is one of the largest components of public sector aquaculture in the eastern U.S. and there is increasing interest in private sector culture. However, the nutritional requirements of walleye are unknown and experimental diets for use in quantifying nutritional requirements have not been identified. We formulated four experimental and four practical diets and fed those to triplicate groups of walleye with an initial weight of 13 g per fish. The experimental diets contained either casein (CAS), casein + gelatin (CG), casein + arginine (CA), or casein + gelatin + crystalline amino acids (CGAA) as sources of amino acids. The practical diets were formulated to mimic salmon grower (SG) and trout grower (TG) diets, a fish meal‐free diet for trout (TFMF), and a walleye grower (WG) diet. Fish were fed twice daily to satiation for 9 wk. Feed consumption, percent weight gain, specific growth rates, feed efficiency, protein efficiency ratio, and protein retention efficiency were not significantly different among fish fed CGAA, SG, and TG, but those values were significantly higher than in fish fed other diets. Weight gain of fish fed CGAA was approximately 80% of that in fish fed SG and 91% of that in fish fed TG. Protein retention efficiency of fish fed CGAA was approximately 69% and 81% of that observed for fish fed SG, and TG, respectively. In general, the carcasses of fish fed diets CGAA, SG and TG had significantly lower moisture and ash concentrations, and higher lipid levels than fish fed other diets. There were no significant differences in carcass protein concentration, muscle proximate composition, or liver lipid concentration among treatments. Livers from fish fed all diets were characterized by microvesicular degeneration and glycogen accumulation in hepatocytes. Results from the study indicate that CGAA can be used as a basal experimental diet in future nutritional research with juvenile walleye and confirms the benefits of trout and salmon grower diets. Fish meal‐free diets formulated around the requirements for rainbow trout were consumed at approximately 80% of the values in fish fed TG and SG, but weight gain was approximately 20% of that in fish fed TG and SG. It appears the nutritional requirements for walleye are different than those of rainbow trout.

Effects of dietary protein level on growth performance, carcass composition and ammonia excretion in juvenile silver perch ( Bidyanus bidyanus)

Juvenile silver perch were fed various dietary protein levels to investigate their growth performance, carcass proximate composition and 24 h postprandial accumulated ammonia excretion. White fish meal was the primary protein source in the study. Eight experimental diets containing 13–55% protein with 15.06 MJ/kg diet were fed to three-replicate eight groups of eight fish (mean weight: 2.72 g) for 8 weeks. Both percent weight gain and feed efficiency significantly increased with increasing dietary protein levels up to 37%, while there were no significant differences for protein levels from 37 to 55%. Application of broken line regression analysis to percent weight gain provided an estimate of 42.15±1.87% dietary protein for maximum growth. The protein efficiency ratio and productive protein value were inversely correlated with dietary protein level. The hepatosomatic index and intraperitoneal fat ratios were also inversely related to dietary protein level. Fish fed diets containing 43% dietary protein had significantly higher condition factor than fish fed lower dietary protein levels, but fish fed only 13% dietary protein had the longest relative gut length. The protein content of the fish carcasses increased with dietary protein levels up to 31%, but no significant difference was found with protein levels higher than 37%. Lipid content decreased with increasing dietary protein levels and dry matter content also slightly decreased. The amount of postprandial ammonia excreted by silver perch within 24 h was linearly related to dietary protein level.

Effects of dietary methylmercury on reproduction of fathead minnows.

We examined effects of dietary methylmercury (MeHg) on reproduction of fathead minnows (Pimephales promelas). Juvenile fish were fed one of four diets until sexual maturity (phase 1): a control diet (0.06 microg Hg g(-1) dry weight) and three diets contaminated with MeHg at 0.88 (low), 4.11 (medium), and 8.46 microg Hg g(-1) dry weight (high). At sexual maturity, male and female fish were paired, again fed one of the four diets, and allowed to reproduce (phase 2). To assess effects of MeHg during gametogenesis, some fish were fed diets during phase 2 that differed from those during phase 1. Spawning success of pairs fed the same diet during phases 1 and 2 was 75% for controls and 46%, 50%, and 36% for the low-, medium-, and high-MeHg treatments, respectively. Spawning success of pairs fed a contaminated diet during phase 1 and a control diet during phase 2 was 63%, 40%, and 14% for the low-, medium-, and high-MeHg treatments, respectively, whereas exposure to dietary MeHg only during phase 2 did not reduce spawning success. Dietary MeHg delayed spawning, and days to spawning was positively correlated with concentration of total mercury in the carcasses of test fish. MeHg reduced the instantaneous rate of reproduction of fish fed the same diets during phases 1 and 2. Both the gonadosomatic index and reproductive effort of female fish were inversely correlated with mercury in carcasses, whereas developmental and hatching success of embryos, 7-d survival, and 7-d growth of larvae were unrelated to mercury concentrations in parental fish or their diets. MeHg decreased reproduction of adult fathead minnows at dietary concentrations encountered by predatory fishes in aquatic systems with MeHg-contaminated food webs, implying that exposed fish populations could be adversely affected by this widespread contaminant.

Fish mortality and physicochemistry in a managed floodplain wetland

Patterns of fish mortality and associated physicochemical factors werestudied during late spring in a managed wetland canal along the lowerMissouri River, Missouri. Mean dawn dissolved oxygen was lower and meanun-ionized ammonia and turbidity were higher during the fish kill thanbefore or after the kill, or than was observed in a nearby wetland canalwhere no fish kill occurred. Dissolved oxygen at dawn and un-ionizedammonia concentrations were at critically low and high levels respectively,so that both likely contributed to the fish mortality. Timing and magnitudeof observed carcasses suggested that Ameiurus melas Rafinesques wasthe most tolerant species for the sizes observed compared to Ictiobuscyprinellus Valenciennes, Lepomis macrochirus Rafinesque, Cyprinus carpio Linneaus, and Lepomis cyanellus Rafinesque.Decreasing mean lengths of fish carcasses during the fish kill for C.carpio, L. cyanellus, and A. melas, indicate that smaller fishes mayhave been more tolerant of harsh environmental conditions than largerindividuals of the same species. Differential mortalities among species andsizes during drawdowns in actively managed wetland pools may haveintentional and unintentional ramifications on wetland and riverine fishcommunity structure, fish-avian interactions, and implementing anecosystem management perspective to restoring more naturalized riverfloodplain wetland functions. Late summer and early autumn draining ofmanaged wetlands might be used to benefit a wider diversity of wildlife andfishes.

Stable Isotopes in Animal Ecology: The Effect of Ration Size on the Trophic Shift of C and N Isotopes Between Feed and Carcass

The feeding ecology of living or extinct animal species is now frequently studied by analysis of stable isotope ratios in small quantities of carcass or remains such as bones or teeth. Although there are numerous papers on these applications in natural systems, the theoretical and experimental basis of this method is weak. In order to evaluate the effect of different feeding levels on the carbon and nitrogen trophic shift, an experiment was carried out in which fish (Nile tilapia, Oreochromis niloticus, initial weight 40.8g) were fed for 4 weeks at three levels from slightly above maintenance to almost satiation. For each treatment, three fish were reared individually. The isotopic ratios of carbon and nitrogen in feeds and fish carcasses were determined and in the case of carbon this was done separately for lipids and lipid-free matter. The trophic shift was calculated at each feeding level from the δ13C and δ15N ratios of feed and fish. There was a significant trend towards higher values for the trophic shift at higher feeding rates in all fractions analysed. Although further research is required, it can be concluded that the effect of feeding level cannot be ignored when the diet of an animal has to be calculated from the ratios of isotopes in its body.

Nicotinic acid supplementation of diets for the African catfish, Clarias gariepinus (Burchell)

Semi-purified diets containing 39% crude protein and 5% lipid were used to identify the qualitative requirement of African cattish, Clarias gariepinus (Burchell), for niacin and to characterize the pathologies associated with a deficiency of this vitamin. After 48 days of feeding, C. gariepinus supplied with the unsupplemented diet had developed severe deficiency symptoms and were subsequently withdrawn from the growth study. Niacin deficiency was characterized by feed refusal, listlessness, weight loss, poor feed utilization and high mortality. The skin overlaying the lateral line of the deficient fish became haemorrhagic and this clinical sign was accompanied by severe anaemia. After 126 days of feeding, fish fed diets containing 17.0 mg niacin kg−1 had also developed a dermopathy. but without anaemia or high mortality. The feeding of diets containing less than 33.1 mg niacin kg−1 resulted in suboptimal feed efficiency and poor protein utilisation. Allometric analysis of proximate composition indicated that carcass moisture, protein and ash were influenced by fish size, and not by dietary niacin content. However, significantly more lipid per unit of weight gain was deposited in the carcasses of fish fed the unsupplemented diet than in fish fed diets containing 17.0mgkg−1. The indicators used in the present study could not be applied to accurately determine a value for niacin requirement. However, until a more accurate assessment is performed, it is recommended that diets for C. gariepinus contain not less than 33.1 mg nicotinic acid kg−1 feed.

Trophic controls on stage transformations of a toxic ambush-predator dinoflagellate.

The toxic dinoflagellate, Pfiesteria piscicida, was recently implicated as the causative agent for about 50% of the major fish kills occurring over a three-year period in the Albemarle-Pamlico Estuarine System of the southeastern USA. Transformations between life-history stages of this dinoflagellate are controlled by the availability of fresh fish secretions or fish tissues, and secondarily influenced by the availability of alternate prey including bacteria, algae, microtauna, and mammalian tissues. Toxic zoospores of P. piscicida subdue fish by excreting lethal neurotoxins that narcotize the prey, disrupt its osmoregulatory system, and attack its nervous system. While prey are dying, the zoospores feed upon bits of fish tissue and complete the sexual phase of the dinoflagellate life cycle. Other stages in the complex life cycle of P. piscicida include cryptic forms of filose, rhizopodial, and lobose amoebae that can form within minutes from toxic zoospores, gametes, or planozygotes. These cryptic amoebae feed upon fish carcasses and other prey and, thus far, have proven less vulnerable to microbial predators than flagellated life-history stages. Lobose amoebae that develop from toxic zoospores and planozygotes during colder periods have also shown ambush behavior toward live fish. In the presence of abundant flagellated algal prey, amoeboid stages produce nontoxic zoospores that can become toxic and form gametes when they detect what is presumed to be a threshold level of a stimulatory substance(s) derived from live fish. The diverse amoeboid stages of this fish "ambush-predator" and at least one other Pfiesteria-like species are ubiquitous and abundant in brackish waters along the western Atlantic and Gulf Coasts, indicating a need to re-evaluate the role of dinoflagellates in the microbial food webs of turbid nutrient-enriched estuaries.

Use of canola oil in the feed of larval and juvenile goldfish, Carassius auratus (L.)

Goldfish were used as a model for the evaluation of canola oil as a lipid source in the feeds of larval and juvenile cyprinids. Goldfish larvae were raised from hatching until 24 weeks of age on diets containing cod liver oil. canola oil or a mixture of the two oils as the lipid source. Survival, weight gain and weight-length relationship did not differ among groups of fish fed the three diets. Carcass fatty acid profiles largely reflected those of the diets except that carcasses of fish fed canola oil contained long chain (n-3) and (n-6) polyunsaturated fatty acids (PUFA) that are not found in canola oil. This indicates that goldfish are capable of producing these fatty acids from 18-carbon precursors. The flesh of fish fed canola oil would be inferior for human nutrition to that offish fed marine oils, due to lower (n-3) PUFA levels. However, the results do indicate that canola oil has good potential as a lipid source in larval cyprinid diets.

Lipid and fatty acid compositions of stream periphyton and Stoneroller Minnows (Campostoma anomalum): trophic and environmental implications

Lipids and fatty acids were analyzed in the herbivorous minnow (Campostoma anomalum) and its predominant food (periphyton) in three streams in eastern Tennessee (East Fork Poplar Creek, Hinds Creek and White Oak Creek). Fatty acid markers were used to explore the trophic relationship between the fish and its algal food. C. anomalum are lipid-rich fish, with a high potential for uptake of hydrophobic pollutants. The mean lipid content of the minnows was 6.5 % of the wet weight in the carcasses, and 26.5 % of the digestive tract. The concentrations of polychlorinated biphenyls (PCBs) in the fish carcasses and guts were directly proportional to the lipid contents of these body portions. Microscopic examination of periphyton in the guts, and the analysis of fatty acid markers showed that green algae dominated periphyton ingested by the minnows in East Fork Poplar Creek (∼90 % of the ingested algal biomass was from chlorophytes). The fatty acid profiles of the minnow guts (including their gut contents), and their lipid stores in East Fork Poplar Creek also reflected extensive ingestion of green algae indicated by an abundance of a fatty acid marker α-linolenic acid (18:3ω3), at 13 % of the total fatty acids. A relatively low biomass of diatoms, and a correspondingly low concentration of a fatty acid characteristic of diatoms (eicosapentaenoic acid, 20: 5ω3) occurred in periphyton from both Hinds Creek and White Oak Creek. Nevertheless, taxonomic and lipid analyses of the minnow gut contents showed that in White Oak Creek diatoms constituted a disproportionately large share of the minnows' diet. The discrepancy in fatty acid profiles between the portion of periphyton in this stream and the gut contents of C. anomalum suggests that the minnows do not consume all portions of the periphyton equally. These results emphasize the applicability of fatty acid analysis to reveal trophic linkages in aquatic ecosystems.

The burrows and physiological adaptations to a burrowing lifestyle of Natatolana borealis (Isopoda: Cirolanidae)

The isopod Natatolana borealis Lilljeborg constructs U-shaped burrows in soft mud, the bore of which closely approximates the width of the occupant. Within artificial burrows, the isopods are largely quiescent and often adopt a position close to one of the burrow openings. Conditions within burrows constructed in the laboratory are moderately hypoxic [11.7 to 14.9 kPa (88 to 112 torr)], with isopods showing discontinuous irrigation behaviour (pleopod beating). Rates of oxygen consumption \((\dot M_{O_2 } )\) (measured at 10°C) are maintained approximately constant over a wide range of oxygen partial pressure (PO2) due, in part, to a pronounced increase in pleopod beat rate. Values for the “critical” partial pressure of oxygen (Pc), the PO2 at which \(\dot M_{O_2 } \) can no longer be maintained independent of PO2, were 2.0 to 3.3 kPa (15 to 25 torr). N. borealis can survive lengthy periods (65 h at 5°C) of anoxia, during which there is a significant reduction in the carbohydrate concentration and an increase in the l-lactate concentration of the tissues. The oxygencarrying capacity of the haemolymph of N. borealis was low. The haemocyanin showed a relatively high oxygen affinity [P50=0.39 kPa (2.99 torr) at 10°C at the in vivo pH of 7.80] and a pronounced Bohr effect (-1.22). These characteristics may be advantageous to a burrowing mode of life and also for the conditions likely to be encountered in fish carcasses into which they burrow en masse to feed.

Taphonomy of crown-of-thorns starfish: implications for recognizing ancient population outbreaks

A field experiment was conducted to determine whether in situ mass mortality of Acanthaster pIanci sub- sequent to a simulated outbreak would leave a recogniz- able signature in surficial reef sediments. Constituent particle analyses comparing sediments that received star- fish carcasses to those that did not revealed that, after a four year interval, the mass mortality was reflected by elevated abundances of starfish ossicles in 1-2 mm and 2-4ram size classes, but not in >4ram and 0.5-1ram size classes. Additional field study of starfish taphonomy revealed that the abundance of starfish ossicles in surficial sediments decreases through two orders of magnitude between two weeks and four years post-mortem, while tumbling experiments suggest that the size distribution of starfish ossicles is modified by physical processes: the 4 mm class. Taphonomic biasing increased the abund- ance of crown-of-thorns starfish (COTS) skeletal elements in the 0.5-1 mm size fraction, while the 1-2ram size and 2-4 mm fractions produced the most reliable signature of starfish mass mortality based on element abundance. Our results demonstrate the importance of taphonomic pro- cesses in altering the original size frequency distribution of the COTS skeleton and their potential for biasing predic- tions of past population levels derived from constituent particle analyses of surficial reef sediments.

An Early Devonian lake and its associated biota in the Midland Valley of Scotland

ABSTRACTThe Tillywhandland fish bed of the Lower Old Red Sandstone in the Strathmore area of the Scottish Midland Valley accumulated in a lake, here called Lake Forfar, which was created suddenly following a period of fluvial deposition. Lake creation may have been due to basin faulting or the disruption of drainage patterns by contemporaneous volcanic activity. The fish bed laminites accumulated in a hydrologically open lake under a seasonal climatic regime. When fully developed, laminites comprise repeated quadruplets of clastic silt/carbonate/organic/green clay–shale laminae averaging 0·5 mm in thickness. Following 2000 years of laminite deposition an increasingly silty succession with thin current-rippled sandstones provided the lake-fill.The fish fauna is dominated by Mesacanthus and Ischnacanthus with rare Euthacanthus, Parexus, Climatius, Vernicomacanthus and Cephalaspis. Most fish carcasses were partially decayed before deposition in the laminites on the poorly oxygenated lake floor. Abundant coprolites are the result of predation on Mesacanthus and small Ischnacanthus, probably by larger Ischnacanthus. Arthropods present include eurypterids (Pterygotus), washed in as near complete exuviae and fragments, and millipeds which were washed in from surrounding terrestrial environments along with plants, of which Parka and Zosterophyllum are common. Bioturbation indicates that conditions were not permanently anoxic during deposition of the laminites.Comparison of our collections with the Mitchell Collection accumulated in the 19th century indicates that Tillywhandland Quarry was the main source of specimens in laminite lithologies labelled ‘Turin Hill’.

Use of salmonid carcasses by vertebrate scavengers

The use of salmonSalmo salarcarrion by ottersLutra lutraand other scavengers along the River Dee in north‐east Scotland was studied by radio‐tagging and individual marking of fish carcasses. More carcasses were available on the Dee than on tributary streams used for spawning, indicating that salmon returned to the river after spawning and died there. The amount of salmon carrion available to terrestrial and avian scavengers along the Dee varied from 6.7 kg. km‐1on an upstream study area to 36 kg. km‐1downstream. Fish carcasses in the Dee were moved by spates up to 20 km but in streams used for spawning less than 1 km. Of 86 carcasses examined in 1990/91, 64 were available to terrestrial and avian scavengers on the bank or awash and of these 45 had been fed upon by otters and 16 by birds. In 1991/92, 23 of 30 carcasses were available to terrestrial and avian scavengers. All had been fed upon, 19 by otters, four by birds. Other carcasses, in shallow water, were not available to terrestrial and avian scavengers. Subsequent scavenging was mainly by otters and continued for up to three weeks after the carcasses were found. HeronArdea cinerea, great black‐backed gullLarus marinusand crowCorvus coronealso scavenged salmon carcasses along the Dee. Great black‐backed gulls were the most frequent scavengers, but heron (dominant to black‐backed gull) was a major scavenger in 1990/91. Crows, subordinate to other scavengers, waited, often in pairs, upon dominant scavengers. There were more scavenging birds downstream and numbers did not change between years. Of 20 salmon carcasses placed in spawning areas eight were probably, two possibly, removed by otters. Otters continued to scavenge carcasses for up to a month. Scavenging by foxesVulpes vulpesand birds followed the removal of fish carcasses from the water by otters. Radio transmitters were removed by otters and left lying alongside carcasses.

Nassariid gastropods as destructive agents in preservation and fossilization of marine fishes

Experimental investigations on the feeding activity of the gastropodNassarius moestus in intertidal environments in the Sea of Cortez (Gulf of California) show them to be effective agents influencing processes of marine fish taphonomy. Time-lapse documentation reveals that potential whole-body preservation of fish carcasses is largely prevented through the rapid destruction of soft tissues, muscles, and ligaments, followed by disarticulation and subsequent disassociation of skeletal elements. Dissociated bones are subject to differential dispersal through hydrodynamic transport and physical wear through abrasion. Transformation of whole-body carcasses into thoroughly defleshed and disarticulated skeletons by large groups of scavenging snails was commonly observed to take place within one tidal cycle. The loss of information during taphonomic processes via destructive biological agents may ultimately bias the fossil record in a significant way and thus have implications for the paleoecological interpretation of fossil teleost assemblages.

The production of Clostridium botulinum type A, B and D toxin in rotting carcasses

Carrion is a major source of botulinal toxin for animals. A type D strain of Clostridium botulinum differed from type A and B strains in producing (1) much higher concentrations of toxin in putrefying mouse carcasses at several different temperatures over a period of 35 days, (2) toxicity that sometimes persisted in mouse carcasses for at least a year, and (3) mouse carcasses with exceptionally high oral toxicity. Fish carcasses were much less favourable than mouse carcasses for type D toxigenesis. The study, together with earlier studies on types C and E, indicated that carrion contaminated with C. botulinum type C or D is likely to be particularly dangerous for animals that may ingest it. This accords with the observation that carrion-transmitted botulism in animals is usually caused by type C or D.