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Large Fish (large + fish)
Selected AbstractsFishing out marine parasites?ECOLOGY LETTERS, Issue 6 2010Impacts of fishing on rates of parasitism in the ocean Ecology Letters (2010) 13: 761,775 Abstract Among anthropogenic effects on the ocean, fishing is one of the most pervasive and extends deepest into the past. Because fishing reduces the density of fish (reducing transmission efficiency of directly transmitted parasites), selectively removes large fish (which tend to carry more parasites than small fish), and reduces food web complexity (reducing transmission efficiency of trophically transmitted parasites), the removal of fish from the world's oceans over the course of hundreds of years may be driving a long-term, global decline in fish parasites. There has been growing recognition in recent years that parasites are a critical part of biodiversity and that their loss could substantially alter ecosystem function. Such a loss may be among the last major ecological effects of industrial fishing to be recognized by scientists. [source] Effects of marine reserve age on fish populations: a global meta-analysisJOURNAL OF APPLIED ECOLOGY, Issue 4 2009Philip P. Molloy Summary 1. ,Marine reserves are widely used for conservation and fisheries management. However, there is debate surrounding the speed of population recovery inside reserves and how recovery differs among species. Here, we determine how reserve effectiveness in enhancing fish density changes with reserve age. We also examine how the effects of protection vary between fished and non-fished species and among species of different body sizes, which we use as a proxy for life history and ecology. 2. ,We meta-analysed over 1000 ratios of fish densities (inside : outside reserves) taken from reserves of 1,26 years old from around the world. 3. ,Overall, older reserves were more effective than younger reserves, with fish densities increasing within reserves by ,5% per annum relative to unprotected areas. Reserves older than 15 years consistently harboured more fish compared with unprotected areas; younger reserves were less reliably effective. 4. ,Large, fished species responded strongly and positively to protection in old (>15 years) and, unexpectedly, in new and young (,10 years) reserves. Small, fished species and non-fished species of all sizes showed weaker responses to protection that did not vary predictably with reserve age. 5. ,We expected large fish to respond more slowly to protection than smaller species. We also expected small species to decline after large fish had recovered (i.e. trophic cascades). Neither prediction was supported. 6. , Synthesis and applications. Our meta-analyses demonstrate that, globally, old reserves are more effective than young reserves at increasing fish densities. Our results imply that reserves should be maintained for up to 15 years following establishment, even if they initially appear ineffective. If protection is maintained for long enough, fish densities within reserves will recover and such benefits will be particularly pronounced for large, locally fished species. [source] Ovary development in Greenland halibut Reinhardtius hippoglossoides in west Greenland watersJOURNAL OF FISH BIOLOGY, Issue 5 2005C. S. Simonsen Maturity in adult female Greenland halibut Reinhardtius hippoglossoides was studied in three areas in west Greenland waters: the inshore area in Disko Bay and two offshore areas, Baffin Bay and Davis Strait. The aim was to monitor maturity changes in the inshore fjords of Disko Bay over an extended period from winter to autumn and compare these findings with specimens from Baffin Bay and the presumed spawning area in Davis Strait. A significant difference in maturity level was observed in and between the three areas. In Disko Bay maturity indices increased significantly in August and September both with respect to the gonado-somatic index (IG) and the size in the leading oocyte cohort. In the period February to May no significant changes were observed. Mature ovaries were only observed among fish >80 cm total length and only among a fraction of these large fish. Offshore areas of Baffin Bay, even though poorly sampled, showed similar signs in the maturity indices as in Disko Bay. Relative to Disko Bay and Baffin Bay, female fish in Davis Strait had more progressed maturity indices. Furthermore, almost all fish in Davis Strait showed signs of progressed maturity contrary to Disko and Baffin Bay. A large proportion of the Greenland halibut in Disko and Baffin Bay apparently did not begin the maturation cycle until very late in their life history or were repeat spawners with a multi-year maturation cycle. These observations could thus support the hypothesis that Greenland halibut have a prolonged adolescent phase. Atresia was highest in the early phases of maturation in Greenland halibut but relatively high levels of atresia were also observed in fish in more advanced maturity phase. The first was ascribed to fecundity regulation while the latter could be linked to the fish's fitness condition but it was not possible to show this with the available condition index. [source] Thermal tolerance and metabolic physiology among redband trout populations in south-eastern OregonJOURNAL OF FISH BIOLOGY, Issue 2 2004K. J. Rodnick Streamside measurements of critical thermal maxima (Tcrit), swimming performance (Ucrit), and routine (Rr) and maximum (Rmax) metabolic rates were performed on three populations of genetically distinct redband trout Oncorhynchus mykiss in the high-desert region of south-eastern Oregon. The Tcrit values (29·4 ± 0·1° C) for small (40,140 g) redband trout from the three streams, and large (400,1400 g) redband trout at Bridge Creek were not different, and were comparable to published values for other salmonids. At high water temperatures (24,28° C), large fish incurred higher metabolic costs and were more thermally sensitive than small fish. Ucrit(3·6 ± 0·1 LF s,1), Rr(200 ± 13 mg O2 kg,0·830 h,1) and metabolic power (533 ± 22 mg O2 kg,0·882 h,1) were not significantly different between populations of small redband trout at 24° C. Rmax and metabolic power, however, were higher than previous measurements for rainbow trout at these temperatures. Fish from Bridge Creek had a 30% lower minimum total cost of transport (Cmin), exhibited a lower refusal rate, and had smaller hearts than fish at 12-mile or Rock Creeks. In contrast, no differences in Ucrit or metabolism were observed between the two size classes of redband trout, although Cmin was significantly lower for large fish at all swimming speeds. Biochemical analyses revealed that fish from 12-mile Creek, which had the highest refusal rate (36%), were moderately hyperkalemic and had substantially lower circulating levels of free fatty acids, triglycerides and albumin. Aerobic and anaerobic enzyme activities in axial white muscle, however, were not different between populations, and morphological features were similar. Results of this study: 1) suggest that the physiological mechanisms that determine Tcrit in salmonids are highly conserved; 2) show that adult (large) redband trout are more susceptible to the negative affects of elevated temperatures than small redband trout; 3) demonstrate that swimming efficiency can vary considerably between redband trout populations; 4) suggest that metabolic energy stores correlate positively with swimming behaviour of redband trout at high water temperatures; 5) question the use of Tcrit for assessing physiological function and defining thermal habitat requirements of stream-dwelling salmonids like the redband trout. [source] Water temperature fluctuations and territoriality in the intertidal zone: two possible explanations for the elevational distribution of body size in Graus nigraJOURNAL OF FISH BIOLOGY, Issue 2 2002C. E. Hernández On the central coast of Chile, distribution of body size in Graus nigra varied with tidal pool height. With the objective of determining whether environmental temperature is one of the possible causes which explains the observed distribution pattern, two behavioural responses were analysed during an experimental period of increasing water temperature: number of opercular movements (an indirect measure of energy expenditure) and activity levels. The interactions of temperature × time and body size × time had a significant effect on the number of opercular movements. At low temperatures (13,15° C), large fish reached a maximum number of opercular movements, while small fish reached a maximum only at high temperatures (23,25° C). The interaction temperature × time had a significant effect on activity levels of different body sizes. In general, large fish appeared to be less active than small fish, however, at very high temperatures (24,26° C) all individuals increased their activity levels. These data indicate that small fish are acclimatized to live in a wider range of temperatures (13,23° C), and, for fish of all body sizes, the highest temperatures (23,26° C) probably constitute a suboptimal microhabitat. Strong territoriality was observed, with large individuals displacing smaller individuals. These data suggest that temperature is an important factor in explaining why large individuals are not present in high tidal pools (high temperatures), whereas territoriality explains why small individuals are not in low tidal pools (habitat of large individuals). [source] An immune-complex glomerulonephritis of Chinook salmon, Oncorhynchus tshawytscha (Walbaum)JOURNAL OF FISH DISEASES, Issue 12 2008J S Lumsden Abstract Chinook salmon from New Zealand were shown to have a generalized membranous glomerulonephritis that was most severe in large fish. Marked thickening of the glomerular basement membrane was the most consistent lesion, with the presence of an electron-dense deposit beneath the capillary endothelium. Severely affected glomeruli also had expansion of the mesangium and loss of capillaries, synechiae of the visceral and parietal epithelium and mild fibrosis of Bowman's capsule. Chinook salmon from British Columbia, Canada with bacterial kidney disease caused by Renibacterium salmoninarum had similar histological lesions. They also had thickened glomerular basement membranes that were recognized by rabbit antiserum to rainbow trout immunoglobulin. This was true only when frozen sections of kidney were used and not formalin-fixed tissue. An attempt to experimentally produce a glomerulopathy in rainbow trout by repeated immunization with killed R. salmoninarum was not successful. Case records from the Fish Pathology Laboratory at the University of Guelph over a 10-year period revealed that a range of species were diagnosed with glomerulopathies similar to those seen in Chinook salmon. The majority of these cases were determined to have chronic inflammatory disease. This report has identified the presence of immunoglobulin within thickened basement membranes of Chinook salmon with glomerulonephritis and supports the existence of type III hypersensitivity in fish. [source] Performance factors, body composition and digestion characteristics of gilthead sea bream (Sparus aurata) fed pelleted or extruded dietsAQUACULTURE NUTRITION, Issue 4 2009B. VENOU Abstract The effects of steam pelleting or extrusion of a commercial feed on performance of 2 g (small) and 40 g (large) gilthead sea bream was studied. In addition the apparent digestibility of diets, gastric evacuation time (GET) and trypsin and amylase activities were measured in large fish. Fish size significantly increased protein and energy productive value, body protein and lipid, liver glycogen and liver lipid, however decreased daily growth index, feed intake and feed utilization, body moisture and hepatosomatic index. Extrusion processing decreased feed intake, more strongly for small fish, and increased daily growth index, feed utilization, protein and energy productive value, body protein and lipid. Digestibility of starch and energy increased with extrusion and GET of extruded feed was double that of steam-pelleted conditioned feed (i.e. 544 min versus 284 min). Digestive enzyme activities approached maximum values after 240 min for the pelleted diet, while those of the extruded continued to increase, at higher rates for amylase than trypsin. Pelleted diet indicated higher moisture for stomach digesta, while the moisture of the intestinal precipitate indicated a higher water-binding capacity for the extruded diet. The overall results indicate a better assimilation of the extruded diet, which could result from its prolonged gastric evacuation. [source] Improving the mechanical characteristics of faecal waste in rainbow trout: the influence of fish size and treatment with a non-starch polysaccharide (guar gum)AQUACULTURE NUTRITION, Issue 3 2009A. BRINKER Abstract This study (3 × 2 randomized factorial design) describes differences in the mechanical properties of faeces from rainbow trout of three size classes (small ,40 g, mid-size ,150 g, large ,650 g) and assesses the effects of a non-starch polysaccharide binder (guar gum). Observations made at the macroscopic level were reinforced by rheological measurements of viscosity and elastic modulus. Mid-sized fish excreted mechanically the most stable faeces, roughly twice as stable as those of small fish and three times more stable than faeces from large fish. The addition of 3 g kg,1 of guar gum saw some mechanical characteristics improve by about 700%. Faeces from large- and mid-sized fish were more easily stabilized than those of small fish. Mechanical recovery potential for faecal samples disrupted by water turbulence was determined. Stability differences observed for different fish size had no significant effect but the improvements imparted by guar gum reduced postfiltration effluent load to about 35% for large fish, about 24% for mid-size and about 22% for small fish. Faecal leaching decreased significantly with increasing stability. Guar gum was shown to have significant potential for improving the treatability of fish faecal waste. [source] Contamination of fish in streams of the Mid-Atlantic Region: An approach to regional indicator selection and wildlife assessmentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2003James M. Lazorchak Abstract The extent of contamination of fish in the Mid-Atlantic Region was evaluated as part of the U.S. Environmental Protection Agency's Monitoring and Assessment Program's regional assessment in 1993 through 1994. Fish assemblages from wadeable streams were dominated by small, short-lived fishes (e.g., minnows, darters, and sculpins) that were more widely distributed and abundant than large fishes typically chosen for tissue contaminant studies (e.g., trout, black bass, sunfish, common carp). Chemical concentrations in whole-fish homogenates exceeded detection limits for mercury, DDT, and polychlorinated biphenyls (PCBs) in 75 to 100% of the stream length assessed using small fishes and 84 to 100% of the stream length assessed using large fishes. Wildlife values (WVs) representing a threshold for toxic effect were developed to allow examination of the spatial extent of potential risk to piscivorous wildlife. For mercury, DDT, dieldrin, and chlordane, estimates of the regional extent of streams where fish contaminant concentrations exceeded the WVs were greater when based on small fishes than on large fishes. However, within the distribution of stream lengths assessed using small and large fishes, the percentage of stream kilometers exceeding the WVs were quite similar. Our data demonstrate that the greater abundance and distribution of small, short-lived fishes provide greater estimates of regional extent of contamination for first- through third-order streams and can be used for regional assessments of potential exposure and effects in wildlife. [source] Effects of gizzard shad on benthic communities in reservoirsJOURNAL OF FISH BIOLOGY, Issue 6 2003K. B. Gido Effects of gizzard shad Dorosoma cepedianum on benthic communities in a large southern reservoir (Lake Texoma, U.S.A.) were examined during two field enclosure and exclosure experiments in which enclosures were stocked at high and low densities in 1998 and 1999, respectively. In both years, chironomid abundance significantly increased in treatments that excluded large fishes from foraging on sediments. Mean abundance of chironomids and ostracods were significantly higher (P < 0·05) in exclosures than enclosures stocked with gizzard shad at 1140,1210 kg ha,1. In 1999, benthic invertebrate abundances did not differ (P > 0·08) between exclosure and enclosures stocked at 175,213 kg ha,1. Per cent organic matter, algal abundance and abundance of other macroinvertebrates in sediments did not differ significantly among treatments in either year. Although chironomid abundance was reduced in gizzard shad enclosures in 1998, food habits from this and other studies showed that adult gizzard shad in Lake Texoma only consumed detritus and algae. It is likely that high sedimentation rates in Lake Texoma limit the ability of gizzard shad to regulate algae and detritus in benthic sediments. Thus, it is concluded that disturbance of benthic sediments by gizzard shad caused the observed reduction in chironomid abundance, rather than through consumption or competition for resources. [source] | |||||||||||||