Small Size Of Fish Research Articles

Abiotic and biotic factors influencing heavy metals pollution in fisheries of the Western Amazon

The escalating industrial and artisanal extraction of natural resources in the Amazon Basin has centered it into the spotlight of global environmental concern. This study deals with the environmental problems of heavy metals pollution and biomagnification, which stem from mining, agricultural, petrochemical, and industrial discharges. We conducted an extensive investigation, analyzing 360 fish specimens representing 58 species, to assess the concentrations of 11 metals (Al, As, Cd, Cr, Cu, He, Mn, Ni, Pb, Zn, and Hg) along the Ecuadorian sections of the Napo and Pastaza watersheds. Stable isotope analyses (δ15N and δ13C) were employed to determine their trophic positions and potential biomagnification risks. Sampling was carried out during two distinct hydrological seasons to capture seasonal variations in metal concentrations. Furthermore, we estimated species-specific daily heavy metal intake levels. The results of our study revealed that 15 fish species and 53 individual specimens exhibited heavy metal concentrations surpassing recommended standards, with elevated levels of Al, As, and Hg posing significant risks to human consumers with daily intakes of 0.46 kg/day. Notably, our investigation unveiled concerning trends, including increased metal concentrations, Hg biomagnification within fish populations from the Pastaza watershed, and an association between smaller fish size and higher metal content. This study provides a crucial baseline for monitoring future environmental changes and understanding the persistent impacts of heavy metal pollution in the Ecuadorian Amazon region and the broader Western Amazon. It underscores the urgent need for sustainable environmental management practices to mitigate the escalating threat to these vital ecosystems.

A Comparison of the Physiological Responses to Heat Stress of Two Sizes of Juvenile Spotted Seabass (Lateolabrax maculatus)

Temperature affects the metabolism of fish, and fish of different sizes have different tolerances to temperature. The aim of this experiment was to compare two sizes of juvenile spotted seabass, Lateolabrax maculatus (with average weights of 57.91 ± 11.57 g and 13.92 ± 2.77 g, respectively) for changes in physiological, biochemical, and molecular mechanisms under acute heat stress. Experimental fish were exposed to acute temperature increasing from 23 °C to 32 °C, and the mortality rate was noted at various heat stress exposures (0, 3, 6, 12, 24, 48, and 72 h). Moreover, serum and liver were obtained before and after heat stress. The activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), superoxide dismutase (SOD), malondialdehyde (MDA), lactic acid (LD), lactate dehydrogenase (LDH), glucose, and hepatic glycogen, and the expression of heat shock proteins (HSP70, HSP90) and apoptosis-related genes (BAX, caspase-3) in two sizes of spotted seabass were measured. Results showed that the contents of AST, ALT, SOD, MDA, LD, and glucose as well as the expression level of BAX and mortality were higher in large spotted seabass than in small spotted seabass within 12 h. These results indicate that the large spotted seabass had higher levels of oxidative stress and more severe liver damage, resulting in a higher mortality. Furthermore, the HSPs expression level of small spotted seabass was higher and the mortality was lower than that of large spotted seabass. Therefore, we considered that the large spotted seabass has lower levels of HSPs expression, causing their physiological response to be elevated to resist heat stress. In conclusion, spotted seabass with larger size has a poorer tolerance to heat stress compared with spotted seabass with smaller size. The smaller fish size was possibly resistant to heat stress by regulating the HSPs expression level in a more active extent.

Comparative Biotic Monitoring of a Modified Denil Fishway and a Pool and Weir Fishway on a Small Tributary in the Upper Trout Region

Modified Denil fishways have a centred gabion containing gravel and are intended to enable the free passage of riverbed-oriented species and invertebrates. An experimental plant was built at a small hydropower station which provided a newly arranged Denil fishway and a pool and weir fishway parallel to one another. It was possible to alternately operate the systems for monitoring purposes owing to the parallel design, allowing an appropriate comparison and analysis of the results to be carried out. The primary objective of this study is to qualitatively and quantitatively compare the size selectivity and ascent numbers between the new development and the conventional construction type. An important component of this study is the test to prove the passage of bullheads in the modified Denil fishway using an experimental set-up. The results of this study depict a similar size distribution of ascended fish in both construction types and thus provide no evidence of selectivity for small fish sizes. Likewise, no deficit of the modified Denil fishway compared with the pool and weir fishway could be proven within the scope of a monitoring. The successful passage of bullheads could be demonstrated in the experiment as well as during monitoring.

Kebiasaan Makanan Ikan Tembang (Sardinella fimbriata) di Perairan Selat Sunda

Fringescale sardinella is a small pelagic fish in the Sunda Strait which has important ecological value. Studying fish food habits is basically to determine the quality and quantity of fish food and the ecological relationship in the tropic level. The aims of this research were to examine the food habits of fringescale sardinella in the Sunda Strait which includes the composition of the type of food, the area of ​​the niche and the overlap of the food niches. Sampling Sampling was conducted from the catch of fishermen who landed at Labuan Coastal Fishing Port, Banten. Fish samples taken during the study consisted of 620 males and 321 females. The results showed that the highest IP value was in the Thalassiothrix frauenfeldii organism, both in male (55%) and female (54%), so that Halassiothrix frauenfeldii which is a class of Bacillariophyceae was the main food for fringescale sardinella, the largest area of ​​food niches is in male was in the medium size class of 9,0028, while the largest area of ​​food niches in female was in the small size class of 8,9609, the largest overlap value of male and female food niches is in the small fish size group (101-129 mm ) with the medium fish size group (130-158 mm) were 0,9062 and 0,8105 respectively.

The Effect of Water Quality on Aquaculture Productivity in Ibanda District, Uganda

Water quality plays a substantial role in maximizing fish productivity. Despite the efforts made by government to improve fish production, there are general complaints about the small size of fish produced in aquaculture systems. This study was conducted in order to assess the effect of water quality on aquaculture productivity in Ibanda District, Uganda. The specific objectives were to examine the status of water quality parameters (temperature, turbidity, pH, alkalinity, Ammonia content, hardness, Carbon dioxide content, and Iron content) and assess their effect on fish pond productivity. Using data from fish farmers and water samples taken from 25 restocked fish ponds in ten sub-counties, the study revealed that of the eight water quality parameters examined only four (average turbidity, alkalinity, hardness, and Carbon dioxide content) were within the acceptable ranges, while Ammonia content, temperature, pH, and Iron content were slightly outside the recommended ranges. In addition, the study revealed that water quality parameters such as temperature, pH, and Ammonia Carbon dioxide, and Iron content had a significant effect on the weight and size of both tilapia and catfish. The study concluded that certain water quality parameters have a detrimental effect on fish farming. There is a need to educate fish farmers on how to maintain water quality at suitable levels in order to improve fish farm productivity in Ibanda district.

Methylmercury bioaccumulation among different food chain levels in the EEZ of Qatar (Arabian Gulf)

Methylmercury (MeHg) concentrations in three different species from different trophic levels with different amounts of Hg exposures were determined for the first time in the EEZ of Qatar. Sampling was conducted during autumn 2017 in two nearshore (Palm Tree and Al-Besheriya Islands) and two offshore locations (Sherawoo and Ishat Islands). Fish muscle and liver tissues were analyzed according to the US Environmental Protection Agency Method 1630. The lowest mean MeHg concentration was found to be 42.3 ppb wet weight in the lower trophic level fish Gerres oyena due to small fish size and trophic level; whereas, the highest MeHg concentration was found in higher trophic level sharks Rhizoprionodon oligolinx and Chiloscyllium arabicum with mean wet weight concentrations of 712 ppb and 166 ppb, respectively. Linear relationships were found between fish body size (weight, length, age) and MeHg concentrations. MeHg bioaccumulation was found to be higher in liver than in muscle tissue; however, there was no significant difference in tissue MeHg accumulation as well as, the concentrations between the four locations. The present study concludes that MeHg in most of the fish tissues is within the allowable limits and pose no threat to public health. Only the higher trophic level shark Rhizoprionodon oligolinx was found to have a MeHg concentration higher than the US EPA advisory level of 0.3 ppm. However, consumers should still be encouraged to eat smaller sized younger fish from lower trophic levels, which would be safer than larger older species from higher trophic levels.

Reproductive biology of the Atlantic mackerel Scomber scombrus Linnaeus, 1758 in Mediterranean coast of Sinai, Egypt.

This work aims to investigate reproductive biology of the Atlantic mackerel (Scomber scombrus L. 1758) to provide biological base for management of its fisheries in the Mediterranean coast of Sinai, Egypt. Monthly samples of S. scombrus were collected from the commercial catch in different landing sites of the Mediterranean coast of Sinai during 2019. The length-weight relation was found as W= 0.0116 L2.9556, W= 0.0077 L3.091 and W= 0.0094 L3.022715 for males, females and combined sexes respectively. Overall sex ratio (males: females) was 1: 1.4 during the period of study. Gonado- Somatic Index (GSI) of females showed that S. scombrus spawn during March, April and May, since GSI peaked in these months (6.5, 7.2 and 5.2 % respectively). The lowest value of GSI of females was recorded in October (0.05%). Lengths at first sexual maturity (Lm) were determined as 23.2 and 23.4 cm for males and females respectively. The absolute fecundity (F) was increasing with the fish length and described by a power equation: F = 0.0014 L5.6414. The relative fecundity gradually increased from 2481.8 to 7599.3 eggs per cm (average 4748.9 eggs / cm). To protect and maintain the stock of Atlantic mackerel in the Mediterranean coast of Sinai, it is recommended to ban using fishing nets of illegal mesh sizes and other destructive fishing methods which catch small fish sizes. Length at first capture should be larger than length at first sexual maturity (> 23.4 cm) and ban fishing nets targeting S. scombrus during its spawning season (from March to May).

Impacts of fish farm structures with biomass on water currents: A case study from Frøya

Impacts of aquaculture fish cages and their biomass on the local water current field is investigated with extensive, full scale field measurements. This is important for the fish welfare as well as for waste transport from open fish cages. The relationships between the current flow rate at various locations close to fish cages are examined at an aquaculture marine site close to Frøya, Norway. This is an area with a complex current pattern due to the bathymetry, rocks and islands, coast current and strong wind conditions. An array of ADCPs (Acoustic Doppler Current Profilers) measured currents. Moreover, CTD and separate temperature profiler instruments were made in order to analyze flow stratification. Two different measurement periods are analysed with 1) small fish size (0,2–0,4 kg) and 2) large fish size (1 kg–5 kg). The field measurements indicate some impact from the biomass on the measured current flow at distances from 90 to 320 m around it. The results are supported by results from the numerical ocean model SINMOD (SINtef MODel).

Species-specific preference heterogeneity in German freshwater anglers, with implications for management

Abstract We used a stated choice experiment answered by 1335 German anglers and fit latent class models to understand preference heterogeneity where context was accounted for by species choice. Information theoretic approaches were used for model ranking, indicating that a three-class latent class model provided the best fit to the data. The three angler classes differed in centrality to life-style and harvest orientation as well as in the general utility experienced by fishing as opposed to not fishing. Moreover, the three angler types varied in their aversion towards cost, collectively suggesting that the three anglers classes differed by psychological commitment to fishing. The three angler types differed in the importance they attached to a range of attributes across several target species, most notably in relation to cost of fishing, catch-related angling qualities and crowding. Both catch rate and average size of the fish in the catch showed evidence of diminishing marginal utility returns, while the probability of catching trophy fish did not. Although not consistently significant across all target species, the most committed angler class benefited most consistently from size of fish, and the intermediately committed angler group from both catch numbers and size. By contrast, the least committed angler group was largely indifferent to many attributes of the fishing experience. Preferences for catch-related attributes and crowding were most pronounced in experiences targeting pike, carp, eel, zander and “other species”. There were no significant preferences for harvest regulations, stocking frequency and the composition of the catch in terms of wild vs. hatchery fish in any of the three angler types, independent of which species was targeted. Collectively, our study reveals the presence of substantial preference heterogeneity, most notably related to catch-related aspects of the fishing experience, crowding and cost of fishing. These preferences, however, are species- and angler-type dependent. Management implications Angler populations are heterogeneous with respect to preferences. Thus, one-size-fits-all policies are unlikely to be optimal for all. Managing freshwater fisheries for high catch rates, large sizes in the catch and limited crowding aligns well with the preferences of more committed anglers across most species and can thus be considered generic management objectives that safeguard high angler well-being of more specialized anglers. Alternatively viewed, alteration of catch prospects and to a lesser degree increased crowding is bound to produce disutility to more specialized anglers, particularly when fisheries move to low catch rates and small fish sizes as fishing pressure rises. Such changes are unlikely to cause large aversion to casual anglers, but this angler group is in the minority compared to more committed fishers, at least in our sample.

Living in an amphidromous world: Perspectives on the management of fish passage from an island nation

Abstract Amphidromy is a form of migratory life history typified by the reproduction of fish in freshwater environments, the early downstream dispersal of post‐hatch larvae to marine environments, and the return of small‐bodied young juveniles to freshwater environments for growth to adulthood. Island freshwater fish communities are frequently dominated by fish species with amphidromous life histories. Amphidromous life cycles leave fish communities highly susceptible to habitat modification and disruptions to connectivity across marine and freshwater environments. This means that managing waterway connectivity is fundamental to their conservation; however, the unique and often geographically restricted amphidromous communities that characterize many small island nations have received little consideration in the development of strategies for the management of fish passage. The ecology and locomotory capabilities of amphidromous species are often poorly studied, partly because their small size at migratory life stages renders current state‐of‐the‐art in situ biotelemetry methods unsuitable. The small size of fish also means that seemingly small obstructions can severely impede migrations. The steps necessary to advance the management of fish passage for island fish communities are: curating and maintaining barrier inventories; evaluating barrier permeability; developing effective barrier mitigation options; and prioritizing restoration and conservation efforts. New methods for understanding the ecology and locomotory capabilities and behaviour of amphidromous fishes are required to advance the management of fish passage for island fish communities. Fish passage solutions that imitate natural streams, such as those promoted in new guidelines in New Zealand, may be the most effective way of improving waterway connectivity; however, integrated approaches to freshwater fish conservation that account for meta‐population dynamics, in combination with the management of fish passage, are necessary to optimize conservation outcomes for amphidromous species.

Feeding habits of small yellow croaker Larimichthys polyactis in the Bohai Sea

PDF HTML阅读 XML下载 导出引用 引用提醒 渤海小黄鱼摄食习性 DOI: 作者: 作者单位: 1. 中国海洋大学水产学院, 山东 青岛 266003;2. 农业部海洋渔业可持续发展重点实验室, 山东省渔业资源与生态环境重点实验室, 中国水产科学研究院黄海水产研究所, 山东 青岛 266071;3. 青岛海洋科学与技术国家实验室海洋渔业科学与食物产出过程功能实验室, 山东 青岛 266237 作者简介: 魏秀锦(1993-),女,硕士研究生,主要从事鱼类摄食生态学研究.E-mail:w_xj4185@126.com 通讯作者: 中图分类号: S932 基金项目: 国家重点基础研究发展计划项目（2015CB453303）；中央级公益性科研院所基本科研业务费资助项目（20603022016003）；山东省泰山学者专项. Feeding habits of small yellow croaker Larimichthys polyactis in the Bohai Sea Author: Affiliation: 1. College of Fisheries, Ocean University of China, Qingdao 266003, China;2. Key Laboratory of Sustainable Development of Marine Fisheries, Ministry of Agriculture;Shandong Provincial Key Laboratory of Fishery Resources and Eco-Environment, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China;3. Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:根据2009年8月至2011年5月4个航次渤海底拖网调查所获得的样品，采用胃含物分析法、K-W检验和聚类分析等方法，对38~218 mm体长范围小黄鱼（）的摄食习性及其随体长、季节的变化进行了研究，并探讨了小黄鱼摄食随海域和年际的时空变化。结果表明：渤海小黄鱼摄食的饵料有40余种，主要以鱼类、虾类和浮游动物为食，优势饵料种类为六丝钝尾虾虎鱼（Euphausia pacifica）、长额刺糠虾（）。渤海小黄鱼在春夏秋这三个季节中，春季的摄食强度最低，夏季和秋季的摄食强度都较高，不同的是夏季摄食率更高，而秋季的摄食量更高。随着体长的增大，渤海小黄鱼的摄食策略发生了相应的变化。从摄食强度分析，在体长较小时，胃饱满指数低，小黄鱼通过高摄食率来提高摄食强度；随着体长的增加，通过高胃饱满指数来提高摄食强度。从摄食的饵料个体分析，小黄鱼采取了随着体长增加摄食饵料个数减少，饵料个体增大的摄食策略。从摄食的饵料组成分析，小黄鱼随着体长增加发生了显著的食性转换现象：体长小于60 mm属浮游动物食性；体长60~99 mm时，属混合动物食性；体长100~119 mm时，属虾食性；体长超过120 mm，包括了虾/鱼食性和鱼食性。小黄鱼摄食的时空变化与环境中优势饵料生物的数量波动密切相关。 Abstract:Based on four bottom trawl surveys conducted in the Bohai Sea from August 2009 to May 2011, 2979 stomach samples of small yellow croaker with body lengths of 38-218 mm were collected. Stomach contents analysis, the Kruskal-Wallis test and the cluster analysis were used to study their feeding habits and ontogenetic, temporal and spatial variations. The results indicated that small yellow croaker fed on more than 40 prey species. Euphausia pacifica, were the dominant prey item. With the increase of fish size, there is a corresponding change in the feeding strategy of the Bohai Sea small yellow croaker. According to the feeding intensity, as indicated by the percentage of empty stomachs (PES) and mean stomach fullness index (MSFI), MSFI was low at the smaller fish size, resulting in the small yellow croaker increasing the feeding intensity as observed by the low PES. With the increase of fish size, the feeding intensity was enhanced by increasing MSFI. According to the prey items, the mean number of prey per fish decreased significantly with the increased fish size, while the mean weight of prey items per fish increased. According to diet compositions, the feeding habits of small yellow croaker had significant ontogenetic variations. Small yellow croaker less than 60 mm in body length mainly fed on the zooplanktivores copepoda, euphausiacea and mysidacea. At 60-99 mm long, it mainly fed on demersal shrimps and copepoda. The frequency of demersal shrimps in the food increased gradually with the increasing fish size, whereas the frequency of copepod decreased. Thus, fish with a 60-99 mm body length belonged to the generalist predators group. At 100-119 mm long, it belonged to shrimp predators group, mainly feeding on demersal shrimps at a frequency of more than 60%, and fish. It still mainly fed on demersal shrimps and fish at greater than 120 mm in body length with the frequency of fish in the food increasing gradually, and ultimately more than the frequency of demersal shrimps (beyond 60%). Thus, fish greater than 120 mm long included shrimp/fish predators and piscivores. The feeding intensity varied significantly across seasons. The feeding intensity of spring was lowest and the feeding intensity of summer and autumn were higher. The difference in the feeding rate was higher (PES was lower) in summer and the feeding amount (MSFI) was higher in autumn. Seasonal variations were also discovered in diet composition. were the dominant preys in spring, were the dominant preys in summer, whereas was the dominant prey in autumn. By analyzing historical data, we found that the feeding habits of small yellow croaker in the Bohai Sea were closely related to the composition and abundance of dominant prey organisms. The temporal and spatial variations in the feeding habits of small yellow croaker is closely related to the fluctuation of dominant prey species in the environment. 参考文献 相似文献 引证文献

Influence of fish swimming on the flow pattern of circular tanks

The effect of swimming fish on the average velocity and velocity profile of a circular tank was studied. Working with different inlet diameters and flow rates, nine different impulse forces (configurations) were evaluated. Each configuration was tested with and without fish, and the effects of two different fish sizes were compared.The velocity profiles in experiments with fish presented a considerable reduction in velocity in the centre of the tank near the outlet, which was a consequence of the increase in the kinematic eddy viscosity due to the turbulence introduced by fish swimming. A flattening of the angular velocity profile was observed in the central area of the tank, which had a radius of about 0.3m (18% of the total volume of the tank).A previous model proposed by Oca and Masaló (2013) was modified in order to better describe the distribution of velocities in the central volume of a tank with swimming fish. The proposed modification was based on Burgers⿿ proposal for a bathtub vortex, which implies the determination of the parameter (1⿿e⿿αr2), where r is the radius and the α values were experimentally obtained for each tank configuration, in which they increased with the impulse force.The average velocities in the tank were proportional to the square root of the impulse force in experiments with and without fish. Experiments with fish presented lower average velocities, which imply higher tank resistance coefficients. At similar stocking densities (14.6kg/m3), the increase in the tank resistance coefficients obtained with small fish sizes (154g) were slightly higher than those obtained with bigger fish sizes (330g).

정치망의 치어혼획저감을 위한 그리드형 탈출장치의 선택성에 관한 연구

This thesis is the fundamental study on the adaptation of escape device for reducing small size of fish in set-net. The escape devices for experiments were made the grid-type devices with three different slit sizes (15, 20 and 25mm). The experiments of size selectivity on escape devices were conducted by using two kinds of species as black rockfish (Sebastes schlegeli) and sea perch (Lateolabrax maculatusi) in the experimental tank. The size selectivity curve was fitted by using a logistic function and the parameters of selectivity curve were estimated by a maximum likelihood method. In the results; 50% selection ranges for the grid-type escape devices with three different slit sizes were; a black rockfish was 13.30, 19.22 and 22.06cm and a sea perch was 17.64, 20.91 and 22.78cm, respectively. The 50% selection range of a black rockfish was wilder than a sea perch about 1.1~1.3 time. Therefore, the small size of fish are able to reduce by using the grid type escape device. However, the optimum slit size of grid should be decided to consider the size of target species and economics of catches.

Long-term changes in fecundity of the Kutum, Rutilus frisii kutum Kamensky, 1901, in the Caspian Sea (Osteichthyes: Cyprinidae)

Changes in length, weight and fecundity of mature females of the Kutum (Rutilus frisii kutum) were compared for the periods 1948–1950, 1974 and 2007 in Iranian waters of the Caspian Sea. The average fork length decreased from 54.1 over 44.7 to 43.9 cm and the average weight from 2181 over 1295 to 1210 g. However, the average condition factor has remained fairly constant and varied between 1.35 and 1.38. The potential fecundity of the Kutum for the three periods also decreased from 106,800 over 74,600 to 64,400 eggs. Size and fecundity of the Caspian Kutum has therefore sharply declined during the last six decades. The reduction of fecundity is apparently the consequence of the shift towards smaller fish size.

The effects of protection measures on fish assemblage in the Plemmirio marine reserve (Central Mediterranean Sea, Italy): A first assessment 5 years after its establishment

This 2-year study was aimed to investigate the early effects of protection measures on fish assemblage in the Plemmirio marine reserve and to evaluate its level of enforcement. Sampling was carried out by means of underwater visual census techniques in four sampling sites within the reserve boundaries and eight outside the reserve. Results showed significant inside/outside differences in the multivariate abundance of fish assemblage. These results were confirmed and exemplified by significant univariate differences between locations for total abundance, Species Richness and diversity of the fish assemblage; values of these metrics were higher inside the reserve than outside. Small fish size and species of low and medium fishing value did not display significant inside/outside differences in abundances whereas medium, large size fish and high value species showed abundances significantly higher inside the marine reserve. Protection effects were particularly evident for large specimens of high fishing value, most of which were exclusively found inside the reserve (Diplodus puntazzo, Epinephelus costae, Mycteroperca rubra, Scorpaena scrofa, Spondyliosoma cantharus, Sciaena umbra and Epinephelus marginatus). The present study provides evidence of a reserve effect on fish populations after only five years since its establishment. This is an extraordinary result likely due to the high level of enforcement observed inside the Plemmirio MPA.

Vaccinated farmed Atlantic salmon are susceptible to spinal and skull deformities

St Petersburg State University, St Petersburg,RussiaSummaryThe aim of this study was to investigate the effects ofvaccination, and starvation after vaccination, on the morphol-ogy of skull bones and vertebral bodies, bone mineralizationand the development of intra-muscular melanin deposits infarmed Atlantic salmon. For this purpose, triplicate groups ofvaccinated (V) or unvaccinated (UV) underyearling smolts(38 g) were fed normal rations (F), or starved for 3 weeks aftervaccination (S) (September 2004), leaving four experimentalgroups (V-F, V-S, UV-F, UV-S). After termination of thestarvation period, all groups were fed a normal ration until thefish reached a normal harvest size (January 2006). There wereno long term effects of starvation on body weight, bonemineralization or deformity incidence. However, at termina-tion, V fish (pooled mean V-F and V-S, 4.4 kg) were overallsignificantlysmallerthanUVfish(pooledmeanUV-FandUV-S, 5.1 kg), and they also developed overall significantly moredeformities in both the skull (pooled mean UV-F and UV-S27%,pooledmeanV-FandV-S81%)andthevertebralcolumn(pooledmeanUV-FandUV-S21%,pooledmeanV-FandV-S41%). These deformities were site-specific in both compart-ments; skull deformities were clearly observed in the ceratohy-ale anterior, while those in the vertebral column were mainlylocated in the tail region (V31–49). There were no significantcorrelations among individual relationships between the skulland vertebral column deformities. UV fish had overall signif-icantly higher vertebral bone total ash content than V fish attermination, butthere werenoeffectsonvaccinationontheashcontentor morphology ofthe vertebrae2 monthsafter transferto seawater. The incidences of intra-muscular melanin depositswere not significantly different between UV and V fish. Theseresults show that vaccination can induce deformities in thevertebral column and ⁄ or skull in farmed Atlantic salmon. Thesite-specificlocationofthedeformitiesinrelationtomechanicalloading is discussed. Furthermore, the results show thatvaccination is not likely the main cause of the current melaninspot problem in Atlantic salmon aquaculture.IntroductionAll farmed Norwegian Atlantic salmon are vaccinated with oil-based adjuvant vaccines before they complete smoltification.This cause a short-term decrease in appetite (Sorum andDamsga˚rd, 2004), induces abdominal lesions that adhere andembed the visceral organs (Poppe and Breck, 1997; Midtlyng,1998) and may induce vertebral deformities (Berg et al., 2006a;Aunsmo et al., 2008), but also gives the fish protectiveimmunity against several diseases (Midtlyng et al., 1996a;Midtlyng, 1998; Lillehaug et al., 2003). Vaccination has alsobeen associated with muscle inflammation and melanin accu-mulation (Koppang et al., 2005), granulomatous uveitis(Koppang et al., 2004), and systemic autoimmunity (Koppanget al., 2008; Haugarvoll et al., 2010). Intra-muscular melanindeposits are a major problem in Atlantic salmon farming, butthe link with vaccination has never been studied. Themechanism behind vaccine induced vertebral deformities hasnot yet been identified. It is not clear whether the vaccine-induced deformities start to develop immediately after vacci-nation or later in the production cycle during on-growth inseawater. Small fish size at vaccination is identified as a riskfactor for vertebral deformities (Va˚gsholm and Djupvik, 1998;Berg et al., 2006a). Haugarvoll et al. (2010) suggest thatvaccine induced deformities can be coupled with systemicautoimmunity. Furthermore, low appetite combined withrelatively good growth in body length has been suggested toimpair bone mineralization and increase the risk for vertebraldeformities in Atlantic salmon (Fjelldal et al., 2007a; Griniet al., 2011). Hence, the short-term decrease in appetite aftervaccination (Sorum and Damsga˚rd, 2004), may make vacci-nated salmon prone to developing vertebral deformities.However, effects of a restricted ration or starvation onpathogenesis in the vertebral column in Atlantic salmon hasnever been tested. In addition, the presence of vaccine-inducedmalformations in other skeletal structures than the vertebralcolumn would indicate a link to a systemic autoimmune origin.The question of whether vaccination affects skeletal structuresother than the vertebral column has never been studied.This study examined the effects of vaccination and post-vaccination starvation on the development of deformities inthe skull and vertebral column. Triplicate groups of vaccinatedand un-vaccinated Atlantic salmon underyearling smolts werefed normal rations or starved for 3 weeks post-vaccination. Allgroups were thereafter fed a normal ration until harvest sizeand their growth performance, severity of abdominal lesions(lesion score), intra-muscular melanin deposits, malformationsin the vertebral column and skull, and mineralization of thevertebral bodies were measured.Materials and methods

Interannual Variability in Growth Rates of Early Juvenile Sablefish and the Role of Environmental Factors

Otolith increments were examined to estimate growth rates of late larvae and early juvenile sablefish from an 8-yr time series (1993-2001), with fish collected from late March to mid-May at the same location off Oregon. The time series spanned a broad range of oceanographic conditions and included an extreme El Nino year (1997-1998) followed by an extreme La Nina (1999). Estimated growth rates overall were rapid for the small size of fish examined and the water temperatures they experienced, averaging 0.4 mm d-1 to 1.0 mm d-1 at fish sizes of 10-40 mm. Growth rates were strongly related to fish size and water temperature. After adjusting for these effects using regression residuals, interannual differences in growth corresponded to large-scale oceanographic indices of productivity and transport in the California Current ecosystem. Growth during the early neustonic stage was correlated with subsequent recruitment to the adult stock except in 1997, when conditions in late winter and early spring apparently were favorable for sablefish growth but survival of the year class was poor, potentially a consequence of reduced productivity as El Nino conditions developed in the summer. Within a year, there was minimal support for the occurrence of growth-dependent mortality, at least within the time frame of our collections. Overall, the results confirm the unusual capacity for rapid growth in small sablefish and are consistent with the general pattern of large-scale environmental controls on larval and early juvenile survival hypothesized for fishes resident in the California Current.

Natural Food Selectivity Changes with Weights of Nile Tilapia, Oreochromis niloticus (Linnaeus), Reared in Fertilized Earthen Ponds

This work was carried out to study the relationship between fish weight and natural food selectivity of Nile tilapia, Oreochromis niloticus (Linnaeus) reared in earthen ponds without supplementary diet and to guide the adaptation of feeding and fertilization strategies. Fish were stocked (1.5 fish/m2) in four fertilized earthen ponds (0.1 ha) for 6 months. Fifty fish were sampled monthly to estimate individual total weight and length and evaluate stomach contents. Fish specimens were categorized into different weight classes: <25 g, 25–50 g, 50–75 g, 75–100 g, and 100–125 g. Overall, the 50–75 g weight class had the highest degree of stomach fullness. The intestinal length-fish length ratio was similar across all fish weights, ranging from 2.9–3.4. Likewise, the composition of food items found in fish stomach was ranked as phytoplankton > detritus > zooplankton. Phytoplankton contribution to gut content increased with increasing fish weight, while detritus and zooplankton contribution decreased. Zooplankton never exceeded 1% of total stomach contents. Cyanobacteria, Chlorophyceae, Bacillariophyceae and Euglenophyceae mostly represented the phytoplankton. Bacillariophyceae dominated the phytoplanktonic portion of stomach contents at small fish size (<75 g/fish), while Chlorophyceae is the dominant group at large fish size (> 75 g/fish). Fish could select Cyanobacteria and Euglenophyceae at all fish weights, meanwhile Chlorophyceae and Bacillariophyceae were eaten with slight selectivity at larger weights..

A Combined Food Web Toxicokinetic and Species Bioenergetic Model for Predicting Seasonal PCB Elimination by Yellow Perch (Perca flavescens)

A commonly used toxicokinetic model was coupled to a bioenergetic submodel optimized for yellow perch and an empirical growth submodel to predict daily PCB elimination flux in three size classes of fish under seasonally variable temperatures. Across seasons, the bioenergetic model predicted highly variable gill ventilation and fecal egestion rates which varied by 74.2-111.2 fold and 35-65 fold, respectively, over the annual cycle. The empirical growth model accounted for seasonal trends in overwintering lipid losses evident for all fish size classes and growth, evident only for the small fish size class, during warm water periods. The toxicokinetic model described seasonal trends in congener specific PCB mass balance of fish, but tended to overestimate PCB elimination for less hydrophobic congeners when the recommended gill transfer efficiency term (Ew) of 0.54 was used. Downward adjustment of Ew to an average value of 0.14 produced the strongest model fit for several low Kow PCBs but had less effect on model performance for mid- to high Kow congeners. The toxicokinetic model was less sensitive to parameters involved in fecal elimination of PCBs when applied to low and mid-Kow PCBs. This study demonstrates the importance of seasonal trends in metabolic rate, growth, and overwintering weight loss as factors that modify PCB toxicokinetics in temperate fish.

Biases associated with the use of underwater visual census techniques to quantify the density and size-structure of fish populations

Estimates of reef fish densities made by divers visually censusing 5 m wide strip transects were compared with capture–resight estimates calculated independently using data on the resighting frequencies of fish marked with colour-coded tags. The difference in density estimates between methods varied between species but with patterns consistent at the three eastern Tasmanian sites studied. Densities of the two most abundant species, the wrasses Notolabrus tetricus and Notolabrus fucicola, showed good agreement between methods. By contrast, populations of the two monacanthids Meuschenia australis and Meuschenia freycineti were underestimated by an order of magnitude in strip transects relative to capture–resight, while populations of the open-water latrid Latridopsis forsteri were overestimated. For all common fish species observed in strip transects, variation in density estimates between divers was extremely low compared to variation between sites and between months. Variation in density estimates between different days within a week and between 50 m blocks located 50 m apart was also negligible; however, residual error associated with variation by a single diver within a block and day was high. Biases associated with changing detectability of fishes in open versus densely vegetated habitats were assessed by algal removal experiments, and were found to be negligible or non-significantly low for five of the six species examined. The exceptional species— N. tetricus—exhibited a 70% rise in fish sighted by diver following algal clearance despite trapping data indicating no increase in fish numbers. Diver estimates of fish length were on average 7% greater than measured lengths. Divers possessed a clear tendency to make increasingly inaccurate size estimates as fish length deviated in either direction from 300 mm. Lengths of 175-mm animals were underestimated by ≈20% and 400-mm fishes were overestimated by ≈10%. These changes in diver bias with fish size were largely independent of fish species, site and diver. The precision of size estimates, as indicated by the standard deviation of bias, also varied with fish size, with values varying from ≈13% at 200 mm fish length to ≈8% at 400 mm length. The decline in precision at small body size largely reflected size intervals used by divers to bin data. Divers appear capable of making more precise size estimates than the 25-mm interval used at small fish sizes.