Pansteatitis in polluted Olifants River impoundments: nutritional perspectives on fish in a eutrophic lake,Lake Loskop,South Africa

This study compares the aetiology of pansteatitis in Lake Loskop, relative to two other impoundments along the Olifants River. Macroscopic and microscopic pathology, age determination and analysis of stomach content, fatty acids and stable isotopes explain the high prevalence of pansteatitis in Oreochromis mossambicus (Peters) and several other species in Lake Loskop. All the dietary indicator comparisons between pansteatitis‐affected and healthy fish fail to support a systemic cause. Pansteatitis in Lake Loskop was linked to size and weight of O. mossambicus, but not to ontogenic age. Fish in Lake Loskop showed abnormally high omega‐3 to omega‐6 fatty acid ratios normally only found in marine fish with no significant difference in degree of assimilation of these fatty acids between pansteatitis‐affected and healthy fish. This explains the vulnerability to, but not the occurrence of, pansteatitis. As a cause for the pansteatitis, these results point towards sporadic vitamin E‐depleting trigger events, known sporadic fish die‐off occurrences that provide surviving fish with a rich source of rancid fats on which to scavenge. The mechanism ties pansteatitis to eutrophication and trophic cascade effects, the intrinsic drivers of the disease and suggests an adaptive management strategy that might be applied by relevant conservation authorities.     

Steatitis in wild sharptooth catfish, Clarias gariepinus (Burchell), in the Olifants and lower Letaba Rivers in the Kruger National Park, South Africa

Large numbers of adult Nile crocodiles, Crocodylus niloticus (Laurenti), died from pansteatitis during autumn and winter 2008 in the lower Letaba and Olifants River gorge in the Kruger National Park, South Africa. Consequently, the health status of fish from these waters was investigated. The study presents the pathological findings in fish inhabiting these rivers within the boundaries of the Park. Changes typical of steatitis were diagnosed in many of the larger specimens of sharptooth catfish, Clarias gariepinus (Burchell), caught within the Olifants River gorge. These fish carried large amounts of mesenteric fat with characteristic small brown granulomata within the adipose tissue. Necrosis and inflammation of the adipose tissues, with characteristic ceroid accumulation within the resultant granulomata and the associated aggregation of ceroid‐containing macrophages, were demonstrated histologically and were typical of steatitis. Other changes included mild thickening and pallor of the gill tissues and swollen, orange, fatty livers. Focal hepatic lipidosis was demonstrated histologically, and special stains revealed storage of large amounts of iron in the livers. Blood smears revealed chromatin clumping in erythrocyte nuclei and nuclear and cell membrane irregularities. This is the first record of steatitis in wild‐caught C. gariepinus.     

Comparison of the lipid properties of healthy and pansteatitis‐affected African sharptooth catfish,Clarias gariepinus (Burchell), and the role of diet in pansteatitis outbreaks in the Olifants River in the Kruger National Park,South Africa

Pansteatitis has been identified in wild populations of sharptooth catfish, Clarias gariepinus (Burchell), and Nile crocodiles, Crocodylus niloticus Laurenti, inhabiting the same waters in the Olifants River Gorge in the Kruger National Park, South Africa. Mesenteric and pectoral fat tissue was investigated microscopically and by fatty acid analysis in healthy and pansteatitis‐affected catfish from both captive and wild populations. Variation in fatty acid composition between pectoral and mesenteric fat was noted. Composition of mesenteric fat differed between fish from various localities as a result of differences in diet. Pansteatitis in the captive population, resulting from ingestion of high amounts of dietary oxidized fat, reflected higher levels of unsaturated fatty acids within the mesenteric fat. Mesenteric fat of pansteatitis‐affected wild catfish was characterized by an increase in moisture content, a decrease in fat content and a decrease in stearic and linoleic acids. The n‐3 to n‐6 fatty acid ratio of mesenteric fat was higher in pansteatitis‐affected wild catfish than in healthy catfish from the same locality, reflecting higher polyunsaturated fat intake by pansteatitis‐affected fish. The possible role of alien, invasive, phytoplankton‐feeding silver carp, Hypophthalmichthys molitrix (Valenciennes), in the aetiology of pansteatitis in both catfish and crocodiles in the Olifants Gorge is discussed.     

The expression of selected genes linked to metabolic homeostasis in obese pansteatitis‐suffering Mozambique tilapia,Oreochromis mossambicus (Peters)

The Oreochromis mossambicus (Peters) population inhabiting Lake Loskop, South Africa, is characterized by a high incidence of obesity and pansteatitis. We investigated potential links between the impaired health of Lake Loskop O. mossambicus and the endocrine system by assessing the expression of selected genes associated with the thyroid and adrenal endocrine axes as well as peroxisome proliferator‐activated receptor gamma (pparg). Moreover, contaminant‐induced thyroid and/or metabolic modulation in Lake Loskop water was evaluated using juvenile O. mossambicus in laboratory exposures. The expression of thyroid hormone receptor alpha (thra) and type 2 deiodinase (dio2) was higher in Lake Loskop O. mossambicus than fish from another population, suggesting a degree of thyroid disruption. The altered gene expression may be a consequence, rather than cause of obesity. Expression of dio2 and pparg was higher in juvenile O. mossambicus exposed to unfiltered compared to filtered lake water, and our data suggest fasting as causative factor. Micro‐organism abundance can therefore be a confounding factor in studies applying molecular markers to test for thyroid modulation by environmental waters. Pansteatitis was not a significant source of variance in the expression of any of the genes investigated, suggesting that the disease is not associated with disrupted endocrine signalling.     

长江下游浅水湖泊石臼湖鱼类资源现状及变化趋势

根据2012-2013年对石臼湖水质和鱼类资源开展的2次调查数据,研究石臼湖水质、鱼类资源现状及演变趋势。采用水质单因子评价方法、营养状态质量指数,结合经济合作与发展OECO富营养湖泊判断标准,研究石臼湖、姑溪河、塘沟河、清水河的水质和富营养化状况;通过商业捕捞的渔获物调查,收集石臼湖和姑溪河鱼类资源数据,分析河网区鱼类种类组成、渔获物结构等渔业资源现状。结果表明,石臼湖及毗邻水域存在一定程度的水污染,且湖区受水量变化影响低于河流区,总体水质状况符合地表水环境质量Ⅲ~Ⅳ类,为富营养状态。石臼湖分布鱼类110种,2012-2013年共调查到54种;其中,石臼湖38种,固城湖33种,姑溪河51种。石臼湖、固城湖和姑溪河主要经济鱼类(数量和重量均超过1%的种类)分别有13、11和9种。石臼湖鱼类主要以鲤[Cyprinus(Cyprinus)carpio]、鲫(Carassius auratus)、鲇(Silurus asotus)等适应静、缓流生境的鱼类为主,并以歺又鱼(Hemiculter leucisculus)、鲫、棒花鱼(Abbotina rivularis)等小型鱼类或小规格个体鱼类(1 000 g)为主;湖区天然渔业资源呈衰退趋势,由于和长江下游干流相通,姑溪河鱼类种类数高于湖区,但其生物量远低于湖区;渔业资源的分布状况与水质状况无明显相关性,与河湖的连通性有关;受枯水期水量偏少、上游和周边来水污染以及高密度水产养殖的影响,石臼湖水质出现氮、磷和有机污染物超标等问题。宜采取源头控污、限制养殖、渔民转产以及人工增殖等措施,保护石臼湖水质,恢复天然渔业资源。     

Characterization of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare (Schultz), and the effect of exposure to methylene blue

Failure to inflate the swim bladder is regarded a major obstacle in the rearing of many fish species. We present a study of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare. A normal developing primordial swim bladder was first discernable at the end of the first day post-hatch (p.h.) as a cluster of epithelial cells with a central lumen, surrounded by presumably mesenchymal cells. Initial inflation occurred on the fourth day p.h. Prior to inflation the swim bladder epithelium consisted of an outer squamous and inner columnar layer. Cells of the inner layer were filled at their basal region with an amorphous material, which disappeared upon inflation. A pneumatic duct was absent, and larvae presented no need to reach the water surface for inflation, suggesting that angelfish are pure physoclists. A model for the role of the amorphous material in normal initial inflation is proposed. Abnormal swim bladders were apparent from the fourth day p.h., and methylene blue (MB) at a concentration of 5 ppm significantly increased the prevalence of SBN. Histologically, abnormal swim bladders in larvae hatched in 5 ppm MB could not be distinguished from those in fish raised under routine conditions (0.5 ppm MB). We suggest that MB may have a teratogenic effect in angelfish.     

Fish navigation in the vertical dimension: can fish use hydrostatic pressure to determine depth?

Fish live in complex volumetric habitats, and as such, face a challenging environment through which to navigate. This problem might be simplified if fish could monitor their depth and determine their position within the water column. One possible cue that they could use to ascertain their vertical position is hydrostatic pressure, which varies linearly with depth. Until recently it was assumed that fish were incapable of using hydrostatic pressure to measure depth as they do not possess a mechanism to sense absolute pressure. However, in a recent article by G. Taylor et al., we describe a novel mechanism whereby fish could determine their depth by using the rate in change of pressure mediated by changes in swim‐bladder volume, together with their vertical speed. This mechanism requires fish to be able to sense changes in pressure using their swim‐bladder. Here, we examine fish sensitivity towards hydrostatic pressure by reviewing the literature from behavioural and physiological experiments. This research suggests that fish are acutely sensitive to the magnitude and sign of hydrostatic pressure changes, via changes in the volume of the swim‐bladder. We argue that fish have the necessary physiological measurements to sense the rate in change of pressure, meaning they are able to use the mechanism proposed by Taylor et al. to determine their vertical location. This has profound implications for the study of navigation through volumes, by providing a reliable global cue that fish can use to determine their depth.     

Effects of dietary proline on swim bladder collagen synthesis and its possible regulation by the TGF‐β/Smad pathway in spotted drum,Nibea diacanthus

Swim bladder is an ideal source of collagen production in fish for improved human health. Proline (Pro) is the main proteinogenic amino acid needed for collagen production. However, the effects of Pro supplementation on the swim bladder collagen synthesis have rarely been evaluated in fish. We determined the effects of dietary Pro supplementation on swim bladder collagen synthesis and its possible signalling pathway in spotted drum, Nibea diacanthus. A total of 450 N. diacanthus (100 ± 3.05 g) were randomly assigned into six treatments and fed with diets supplemented with different levels of Pro (0, 2.5, 5, 7.5, 10 and 12.5 g/kg of dry diet, hereafter P0, P1, P2, P3, P4 and P5, respectively) for 8 weeks. At the end, we evaluated collagen synthesis in swim bladder and the expression of genes related to TGF‐β/Smad pathway in the fish. Dietary Pro levels increased significantly the contents of crude protein, total collagen (TC) and the levels of some amino acids in swim bladder than the control diet (p < .05). The optimum amount of dietary Pro inclusion in diets for swim bladder collagen synthesis in N. diacanthus was 7.6 and 7.5 g/kg based on crude protein and TC in swim bladder, respectively. Dietary Pro levels increased significantly the proline 4‐hydroxylase (P4H) content in fish serum, swim bladder, muscle and liver tissues than control (p < .05). The relative expression of collagen type I alpha 1 (COL1A1), alpha 2 (COL1A2) and mothers against decapentaplegic homolog 2 (Smad2) genes in liver and swim bladder initially increased significantly as the concentration of Pro and later decreased (p < .05). Similarly, the relative expression of transforming growth factor beta (TGF‐β), P4Ha2 and P4Ha3 genes in the swim bladder increased significantly as dietary Pro levels increased (p < .05). Using K‐means clustering analysis, dietary proline partly promoted collagen accumulation in swim bladder through upregulation of Smad2 and TGF‐βRT genes. Taken together, Pro affected the collagen metabolism in swim bladder, probably by regulating the TGF‐β/Smad pathway, most likely via transient overexpression of Smad2 gene.     

Fatty Acid Composition of Muscle,Liver, and Adipose Tissue of Freshwater Fish from Lake Victoria,Uganda

Fish oils may differ in fatty acid (FA) composition depending on diet. Oils extracted from muscle, liver, and adipose tissue of Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus), silver fish (Rastrineobola argentea), lungfish (Protopterus aethiopicus), Victoria squeaker (Synodontis victoriae), and two catfishes (Clarias gariepinus and Bagrus docmac) from Lake Victoria, a tropical freshwater lake, were evaluated for FA composition. Oil contents of muscles, livers, and adipose tissues were in the range of 3.16 to 13.8%, 3.62 to 53.4%, and 28.8 to 42.4%, respectively. Omega-3 polyunsaturated FA, particularly alpha-linolenic (ALA), eicosapentaenoic (EPA), docosapentaenoic (DPA), and docosahexaenoic (DHA) acids, were found to be in substantial amounts in oils from all seven fish species. Ratios of polyunsaturated FA to saturated FA (0.79 to 1.18) were in the range considered adequate for normal health. Overall, the results show that the fish species studied are a rich source of omega-3 polyunsaturated FA.     

4种常见淡水养殖鱼类目标强度测定与差异分析

鱼类目标强度(target strength)的测量是渔业声学技术研究和应用的核心内容之一。2015年6―10月,在小型水槽内使用Bio Sonics DT-X(199kHz)科学探鱼仪发射水平声波,测量了4种共29尾不同鳔室结构的淡水养殖鱼类体侧向及背腹向(180°范围)的目标强度,并拍摄X光影像以了解鱼体鳔室结构及特征。其中瓦氏黄颡鱼(Pelteobagrus vachelli)7尾、鳜鱼(Siniperca chuatsi)9尾、鲫鱼(Carassius auratus)6尾、草鱼(Ctenopharyngodon idellus)7尾。结果显示,单体鱼目标强度与声波入射角度具有cos三次方函数关系,体侧向与背腹向上最大目标强度均出现于鱼体主轴垂直于入射声波时,最小目标强度出现于头尾方向朝向声波时,与最大目标强度相差10dB。不同种鱼类体侧向平均目标强度略大于背腹向0.5~5dB。单室鳔鱼类目标强度比相近体长的两室鳔鱼类小。对4种鱼类的目标强度与鱼体相关生物学指标进行主成分分析,体侧向与背腹向目标强度主要受体长、鳔长和鳔长/鳔高值的影响较大。通过目标强度与实验鱼全长、体长、体重的线性回归,获得体侧和背腹入射方向目标强度与3个生物学参数的关系式。本研究通过分析不同鳔室形态鱼种的回波特征差异,辅助判别长江内常见鱼类(如瓦氏黄颡鱼、鱖鱼、鲫鱼等)的声学信号,结果对于淡水水域水平原位监测时分析评估资源量相关参数具有参考意义。     

三峡水库高、低水位下开县汉丰湖鱼类资源变化特征

2012年10-11月三峡水库高水位期以及2013年5-6月三峡水库低水位期调查了汉丰湖的鱼类资源,研究三峡水库高、低水位下汉丰湖鱼类种类组成、优势种类、生物多样性以及群落相似性,并对不同水位下汉丰湖鱼类群落结构的扰动特征和增殖放流情况进行了辨识和探讨。共采集到鱼类17 553尾,42种,隶属于4目7科31属。其中三峡水库低水位时采集到鱼类33种,高水位时采集到鱼类34种。汉丰湖优势种类在三峡水库低水位时为银鮈Squalidus argentatus、似鳊Pseudobrama simoni、歺又鱼Hemiculter leucisculus、蒙古鲌Culter mongolicus mongolicus和鲤Cyprinus(Cyprinus)carpio;在三峡水库高水位时为似鳊、鲤、鲫Carassius auratus、张氏歺又鱼Hemiculter tchangi和鲇Silurus asotus。汉丰湖鱼类Shannon-wiener多样性指数(H’)、Simpson优势度指数(D)、Pielous均匀度指数(E)和Margalef种类丰富度指数(R)在三峡水库低水位时分别为1.63、0.67、0.46和3.52;在三峡水库高水位时分别为2.15、0.80、0.61和4.34。三峡水库低、高水位时汉丰湖鱼类群落结构的Bray-Curtis相似性仅为26.52%,喜缓、静水生境的银鮈、张氏歺又鱼、鲤、歺又鱼、鲫、鲇、似鳊和蒙古鲌是群落结构差异的主要种类,累积差异贡献率为90.67%。汉丰湖鱼类群落在高水位时受到中等程度的干扰,而在低水位时受到严重干扰。建议每年均放流鲢、鳙、草鱼并进一步加大放流规模。     

Degradation of the crocodile population in the Olifants River Gorge of Kruger National Park,South Africa

• 1. Top predators such as crocodiles often reflect ecosystem degradation. The recent spate of close to 200 Nile crocodile deaths may reflect the ecosystem state of the Olifants–Letaba River system in the Kruger National Park. This paper investigates whether the crocodile deaths were indeed the consequence of a rare and perhaps acute event given the variability in annual population growth rates of crocodilians.
• 2. Spotlight‐ and helicopter‐based surveys designed to correct for availability and detectability bias were used to estimate population sizes of crocodiles from 2008 to 2010 in and around the Olifants River Gorge, the focal area of crocodile deaths.
• 3. Correction factors derived from individually observed crocodiles for both spotlight‐ and helicopter‐based counts were lower than those typically used for Nile crocodiles as well as other crocodile species. Even so, corrected spotlight‐ and helicopter‐based estimates were comparable and the number of crocodiles in the focal study area declined significantly from 780 (95% CI: 637–1222) to between 460 (spotlight estimate, 95% CI 375–665) and 505 (aerial estimate, 95% CI: 559–1746) during the period of crocodile deaths. The average annual decline of 35% was at the lower end of the distribution of annual population growth rates across the rivers of Kruger National Park.
• 4. The crocodile deaths reflect a possible rare event that suggests a degraded crocodile population, possibly the consequences of broad‐scale cascades of environmental deterioration of the Olifants–Letaba River system.
• 5. Even so, the potential risk of local demise of the population in the focal study area in the short term may be diminished through evolutionary, demographic and spatial resilience inherent within crocodiles that can accommodate the as yet unknown disease dynamics of pansteatitis. Copyright © 2011 John Wiley & Sons, Ltd.

     

Sarcoma of the swim bladder of Atlantic salmon (Salmo salar L.)

A neoplastic disease of the swim bladder of farmed Atlantic salmon (Salmo salar L.) was investigated. The tumour was classified as a leiomyosarcoma and had a detected prevalence of 4.6% of a population of 500 second-year sea fish.     

Genetic differentiation of the bronze featherback Notopterus notopterus between Mekong River and Tonle Sap Lake populations by mitochondrial DNA analysis

ABSTRACT:   Although the bronze featherback Notopterus notopterus is an important fish in South-East Asia, the population structure has not been investigated. In this study, genetic diversity and population structure of the bronze featherback were examined using nucleotide sequence analysis of the mitochondrial DNA control region for 332 fish collected from Tonle Sap Lake and the Mekong River in Cambodia. The average nucleotide diversity (π) of all samples was 0.033, and the Mekong River samples had higher nucleotide diversity (0.034) than Tonle Sap Lake samples (0.028). The nucleotide diversity between the lake and river samples varied from 0.029 to 0.037. The genetic differentiation between the river and lake populations was also supported by the pairwise F -statistic values and hierarchical analysis of molecular variance, indicating that the Tonle Sap Lake population is genetically isolated from the population in main stream of the Mekong River.     

鄱阳湖刀鲚的渔汛特征及渔获物分析

通过探究鄱阳湖刀鲚(Coilia ectenes)的渔汛特征和渔获物现状,为有效地保护其种群资源提供科学依据。2013-2014年在鄱阳湖设置3个调查点,对刀鲚进行逐月采样调查,共取样986尾、41.54 kg,随机抽样调查不同捕捞网具的整船次鄱阳湖刀鲚渔获物数据,测量体长、体重等生物学参数。采用Pearson相关分析刀鲚单船日渔获重量WB与水文因子关系。结果表明,鄱阳湖刀鲚体长范围为17.9~38.1 cm,其中21.2~23.6 cm是优势体长组,占总个体数的37.02%;体重范围为14.3~198.2 g,其中25~40 g是优势体重组,占总个体数的57.20%。鄱阳湖刀鲚体长L(cm)和体重W(g)幂函数方程为:W=0.0019L3.1378(R2=0.8997;n=986;P0.01)。湖口水域刀鲚出现时间主要集中在每年的5-6月,高峰期在6月,7月很少见;单船渔获数量NB为(3.2±4.1)尾/d,单船渔获重量WB为(0.12±0.11)kg/d。湖口水域刀鲚单船渔获重量WB与该水域水位、流量均呈显著正相关(P0.05),WB与水位的相关性更为显著。与历史资料相比,鄱阳湖刀鲚渔获规格以小个体居多;渔汛稍有推迟,持续时间大幅度缩短;种群规模急剧缩小,表明刀鲚资源正在严重衰退。     

洞庭湖水系资江干流鱼类资源现状调查

资江作为洞庭湖一级支流,对洞庭湖乃至长江水系鱼类资源的维持或补充有着重要作用。为了解资江的鱼类资源现状,于2010年11月～2012年12月对湖南境内资江干流鱼类资源进行调查。共采集鉴定鱼类82种（包括1种湖南鱼类新纪录,2种引进种）,隶属7目18科52属。种类组成以鲤科鱼类为主,占48．78％。鱼类物种数按上、中、下游依次增加,分别为52种、73种和77种,其中上游与中、下游之间鱼类群落为中等相似,中游与下游鱼类群落为极相似。资江鱼类在洄游、摄食、栖息习性等生态类型上呈现多样化特征。调查江段渔获物组成虽存在差异,但主要以鲫（ Carassius auratus ） 、鲤（Cyprinus carpio ）、蟹（ Hemiculter leucisculus） 、翘嘴鲐（Culteralburnus）、蒙古铂（emongolicus）、蛇绚（Saurogobiodabryi）、鲇 （ Silurus asotus ） 和黄颡鱼（ Pelteobagrus fulvidraco ） 等湖泊定居性鱼类为主,“四大家鱼”等洄游性鱼类所占比例极低,鱼类小型化现象明显。     

Swim bladder function and buoyancy control in pink snapper (Pagrus auratus) and mulloway (Argyrosomus japonicus)

Physoclist fish are able to regulate their buoyancy by secreting gas into their hydrostatic organ, the swim bladder, as they descend through the water column and by resorbing gas from their swim bladder as they ascend. Physoclists are restricted in their vertical movements due to increases in swim bladder gas volume that occur as a result of a reduction in hydrostatic pressure, causing fish to become positively buoyant and risking swim bladder rupture. Buoyancy control, rates of swim bladder gas exchange and restrictions to vertical movements are little understood in marine teleosts. We used custom-built hyperbaric chambers and laboratory experiments to examine these aspects of physiology for two important fishing target species in southern Australia, pink snapper (Pagrus auratus) and mulloway (Argyrosomus japonicus). The swim bladders of pink snapper and mulloway averaged 4.2 and 4.9 % of their total body volumes, respectively. The density of pink snapper was not significantly different to the density of seawater (1.026 g/ml), whereas mulloway were significantly denser than seawater. Pink snapper secreted gas into their swim bladders at a rate of 0.027 ± 0.005 ml/kg/min (mean ± SE), almost 4 times faster than mulloway (0.007 ± 0.001 ml/kg/min). Rates of swim bladder gas resorption were 11 and 6 times faster than the rates of gas secretion for pink snapper and mulloway, respectively. Pink snapper resorbed swim bladder gas at a rate of 0.309 ± 0.069 ml/kg/min, 7 times faster than mulloway (0.044 ± 0.009 ml/kg/min). Rates of gas exchange were not affected by water pressure or water temperature over the ranges examined in either species. Pink snapper were able to acclimate to changes in hydrostatic pressure reasonably quickly when compared to other marine teleosts, taking approximately 27 h to refill their swim bladders from empty. Mulloway were able to acclimate at a much slower rate, taking approximately 99 h to refill their swim bladders. We estimated that the swim bladders of pink snapper and mulloway ruptured after decreases in ~2.5 and 2.75 times the hydrostatic pressure to which the fish were acclimated, respectively. Differences in buoyancy, gas exchange rates, limitations to vertical movements and acclimation times between the two species are discussed in terms of their differing behaviour and ecology.     

Differences in Ichthyophonus prevalence and infection severity between upper Yukon River and Tanana River chinook salmon, Oncorhynchus tshawytscha (Walbaum), stocks

Two genetically distinct populations of chinook salmon, Oncorhynchus tshawytscha (Walbaum), were simultaneously sampled at the confluence of the Yukon and Tanana rivers in 2003. Upper Yukon-Canadian fish had significantly higher infection prevalence as well as more severe infections (higher parasite density in heart tissue) than the lower Yukon-Tanana River fish. Both populations had migrated the same distance from the mouth of the Yukon River at the time of sampling but had significantly different distances remaining to swim before reaching their respective spawning grounds. Multiple working hypotheses are proposed to explain the differences between the two stocks: (1) the two genetically distinct populations have different inherent resistance to infection, (2) genetically influenced differences in feeding behaviour resulted in temporal and/or spatial differences in exposure, (3) physiological differences resulting from different degrees of sexual maturity influenced the course of disease, and (4) the most severely infected Tanana River fish either died en route or fatigued and were unable to complete their migration to the Tanana River, thus leaving a population of apparently healthier fish.     

兴凯湖鱼类群落结构变化与渔业资源利用

2012年5月-10月,对兴凯湖鱼类及渔业资源利用状况进行了调查,2012年渔产量约为295t,工作渔船209条,期间共统计渔获物1081kg,生物学测定803尾,经鉴定共有鱼类50种。近年来,兴凯湖生态环境的改变导致鱼类种群结构变化,渔获物个体趋向低龄化、小型化,产量持续下降。本研究整理了历史数据并将其与本次调查结果进行对比,分析渔获物组成特征以及渔产量动态变化特点,找出鱼类群落结构的变化趋势,提出了未来兴凯湖渔业资源可持续利用的建议。     

基于鱼类食性的白洋淀食物网研究

2009年6月至2010年5月,对白洋淀8个典型采样点进行了调查,分析了白洋淀鱼类的食性、营养级和食物网特征,绘制了鱼类食物网及能量流动途径。结果显示,白洋淀现有鱼类25种,其食性类型分为草食性、浮游生物食性、底栖生物食性、游泳动物食性、浮游生物＋底栖生物、底栖生物和游泳动物食性共6种;白洋淀的鱼类营养级可分为草食性、...