Pathogenesis and epidemiology of spontaneous exophthalmos in the West Australian dhufish, Glaucosoma hebraicum Richardson

The West Australian dhufish, Glaucosoma hebraicum Richardson (family Glaucosomatidae) is a potentially valuable aquaculture species, but spontaneous exophthalmos is common in freshly caught and cultured dhufish. To investigate the epidemiology and pathogenesis of exophthalmos in tanks of wild-caught and captive-bred dhufish, records of culture conditions, the prevalence of lesions and pathological examinations were used to study the disease and associated environmental and management factors. Naturally occurring cases of exophthalmos that were examined were mostly unilateral and occurred more frequently in summer months during periods of increasing water temperature. In 15 affected eyes that were examined histologically gas bubbles and haemorrhages were consistently present in the choroid. In some, gas bubbles and haemorrhage were also present in retrobulbar tissues associated with perforation of the sclera. Oxygen concentrations were measured in 12 exophthalmic eyes and concentrations of 50–73% were recorded in gas bubbles in the anterior chamber of three of these that were acute cases. Very low oxygen tensions were recorded at the retinal–vitreal junction of four eyes with retrobulbar haemorrhages indicating that there may have been disruption of arterial blood supply to the choroid in chronic lesions or with perforation of the sclera. The results of experiments to determine the significance of exercise, high water temperature, sudden increases in light intensity, fish handling or tank cleaning indicate that exercise and/or high water temperature (25.5 °C) may be important risk factors for the development of exophthalmos in dhufish. Possible mechanisms for the formation of gas bubbles and haemorrhage in the choroid are discussed.     

The histopathology of acute and chronic infections of rainbow trout Salmo gairdneri Richardson with eye flukes, Diplostomum spp.

Abstract. A histopathological study was carried out on rainbow trout suffering from acute and chronic diplostomiasis. Clinical signs were few in acutely infected fish but in chronic cases fish were blind, exophthalmic and emaciated. Acute infections resulted in subcapsular cataract formation with varying capsular change. Chronically infected fish frequently showed lens dislocation, capsular rupture or duplication and the formation of Elschnig's pearls and Wedl cells. Phacogenic uveitis was seen in many fish with capsular rupture and retinal detachment frequently occurred as a sequal to vitreous detachment.     

High abundance of larval rockfish over Cobb Seamount, an isolated seamount in the Northeast Pacific

The larval fish community in the region of Cobb Seamount (500 km west of Oregon) is dominated by myctophid species commonly encountered in the subarctic North Pacific. However, during a survey in June 1992, the ichthyoplankton community within 30 km of the seamount summit was almost completely dominated by larvae of various rockfish ( Sebastes ) species. Given their very small size (and hence very young age) and the fact that they occurred only rarely in samples collected > 30 km from the seamount summit, we conclude that these Sebastes larvae were produced locally over Cobb Seamount. Previous studies have shown that the Cobb fish fauna is dominated by various Sebastes spp. and that, unlike other fish present on the seamount, the rockfish populations may be self-recruiting. We suggest that a persistent clockwise (i.e. downwelling) eddy, consistent with a stratified Taylor cone, plays a critical role in retaining larval rockfish over Cobb Seamount and may contribute to the process of self-recruitment. The key to the success of rockfish on Cobb and other shallow Northeast Pacific seamounts seems to be linked to their viviparous life history.     

Development of Thyroid Follicles and Changes in Thyroid Hormones During the Early Development of Korean Rockfish Sebastes schlegeli

The development of thyroid follicles and the change of thyroid hormone concentrations in whole body were examined, and the relationship between thyroid follicle differentiation and growth were also studied during early development of Korean rockfish Sebastes schlegeli . Total length (TL) and body weight (BW) of larva at parturition were 6.3 ± 0.1 mm and 3.6 ± 0.1 mg respectively. The larvae transformed to juveniles from 20 to 30 d after parturition with continuous growth. The thyroid primordium of the rockfish was observed histologically in newly born larvae, suggesting that the thyroid primordium may have been formed during yolk-sac larval stage after hatching as with other marine telosts. In addition, although the Korean rockfish is a viviparous fish, the developmental features of the thyroid gland in number, size and shape are very similar to the general development features of marine oviparous fish. As the larvae grew, the thyroid follicles of Korean rockfish increased in number, became variable in size, and changed from the normal spheroid/ovoid shape to more irregular forms in shape after parturition, and then concentrated mostly along the areas immediately adjacent to the ventral aorta. In addition, thyroid cell height and thyroid hormone concentrations were related with physiological activity at a specific developmental stage.     

Deformity of agglutinated pelvic fin membrane in hatchery-reared black rockfish Sebastes inermis and its application for stock separation study

ABSTRACT:   This study is the first to report on the high occurrence of agglutinated pelvic fin membrane deformities in hatchery-reared black rockfish Sebastes inermis . For 5 years, this symptom was marked in hatchery-reared fish, with 58.7% of fish deformed on average (varying between 46.7 and 72.0%). The deformity was a peculiarity in hatchery-reared fish, but is negated in wild fish, and was not related to whether the fish broodstock originated from the wild or from a hatchery. Mark–release experiments showed that deformed fish were almost the same as normal hatchery-reared fish in growth and survival rates, and, theoretically, the recapture numbers of hatchery-stocked fish, estimated by deformity, almost coincided with actual recapture numbers, confirmed by otolith tagging. The results of the present study indicate that deformity in hatchery-reared black rockfish is useful as a stock separation tool.     

Recovery potential of black rockfish,Sebastes melanops Girard,recompressed following barotrauma

Overfished species of rockfish, Sebastes spp., from the Northeast Pacific experience high bycatch mortality because of ‘barotrauma’, a condition induced from the rapid change in pressure during capture. Field experiments show that it may be possible for rockfish to recover from barotrauma if quickly recompressed; however, no work has followed the physiological recovery of rockfish after recompression or determined whether it is possible for rockfish to survive barotrauma in the long term. Barotrauma was induced in adult black rockfish, Sebastes melanops Girard, from a simulated depth of 35 m, followed by recompression. Blood and selected tissues (eye, heart ventricle, head kidney, liver, rete mirabile and gonad) were sampled at days 3, 15 and 31 post‐recompression to evaluate the tissue‐ and physiologic‐level response during recovery. No mortality from barotrauma occurred during the experiments, and feeding resumed in 80% of both treatment and control fish. The primary injury in treatment fish was the presence of a ruptured swimbladder and/or a ruptured tunica externa (outer layer of swimbladder), which was slow to heal. Blood plasma was analysed for glucose, sodium, chloride, potassium, calcium, phosphorus, insulin‐like growth factor‐1 and cortisol. Plasma analyses indicated no strong effects because of barotrauma, suggesting overall handling stress outweighed any effect from barotrauma. Rockfish with ruptured swimbladders may face compromised competency in the wild; however, it appears the majority of black rockfish decompressed from 35 m have a high potential for recovery if recompressed immediately after capture. This research suggests recompression could be a valuable bycatch mortality reduction tool for rockfish in recreational fisheries.     

人工鱼礁区不同网目尺寸单片刺网对许氏平鲉和大泷六线鱼的选择性

为探究人工鱼礁区单片刺网对许氏平鲉(Sebastes schlegeli)和大泷六线鱼(Hexagrammos otakii)的选择性, 于 2021 年 10 月在荣成北部人工鱼礁区使用 4 种网目尺寸(40 mm、50 mm、60 mm、70 mm)的单片刺网进行选择性实验。在 SELECT 模型的架构下, 使用 Normal、Lognormal、Gamma、Bi-normal 模型进行选择性拟合, 根据赤池信息指数(AIC)和模型残差(MD)选择最佳拟合模型。结果表明: Lognormal 模型拟合效果最佳, 其 AIC 值和 MD 值均为最低值。根据 Lognormal 模型, 不同网目尺寸许氏平鲉的模型拟合长度分别为 114.23 mm、142.79 mm、 171.35 mm、199.90 mm; 大泷六线鱼的模型拟合长度分别为 129.67 mm、162.09 mm、194.51 mm、226.92 mm。许氏平鲉和大泷六线鱼的体长与最大剖面周长的线性关系分别为: G=0.2877L+0.7463(R² =0.6722), G=0.2468L– 3.8531(R² =0.6851)。选取 150 mm 作为许氏平鲉和大泷六线鱼的理论成熟体长(MBL)进行分析, 结合幼鱼留存比例, 发现网目尺寸为 60 mm 和 70 mm 的刺网能够保护人工鱼礁区许氏平鲉和大泷六线鱼的幼鱼资源。研究结果可为人工鱼礁区渔业资源的管理和养护提供参考。     

Evidence of homing of black rockfish Sebastes inermis using biotelemetry

ABSTRACT: The black rockfish Sebastes inermis is one of the most important fishery species along the coast from southern Hokkaido to Kyushu, Japan and is often found in rocks and Zostera areas. We conducted biotelemetry using coded ultrasonic transmitters to clarify the movement of the black rockfish that inhabited the seawall of the Kansai International Airport. We released 25 black rockfish at two points. One was the airport seawall and the other was side shallows off the Sensyu district. Seventeen black rockfish returned to their capture site after release. We used the V -test to determine whether the direction of movement was random or orientated. The black rockfish moved at random along the seawall within some hours after release ( P  > 0.05). Four hours after release, they moved to their home site intentionally ( P  < 0.0025).     

Diets of top predators indicate pelagic juvenile rockfish (Sebastes spp.) abundance in the California Current System

Diets of top predators may be useful indicators to the availability of forage fish in marine ecosystems. Juvenile rockfish (young‐of‐the‐year Sebastes spp.) compose a significant part of the diet for many predators in the central California Current, including chinook salmon (Oncorhynchus tshawytscha), and several species of marine birds and mammals. Herein, we develop annual indices of juvenile rockfish relative abundance by collating time series data sets on: (i) the proportion of rockfish in the diet of three species of seabirds breeding on Southeast Farallon Island (1975–2002); (ii) the number of rockfish in chinook salmon stomachs (1980–99); and (iii) the abundance of rockfish captured in scientific mid‐water trawl net surveys (1983–2002). We used Principal Component Analysis (PCA) to combine indices, and refer to these as ‘Multivariate Rockfish Indices’ (MRI). Combining time series verifies the patterns shown by each alone and provides a synoptic perspective on juvenile rockfish relative abundance. The diets of predators with the largest foraging ranges (Common Murre, Uria aalge) and chinook salmon co‐varied strongly with the net samples, and appear to be the best indicators. The salmon also sampled species of Sebastes not caught in the nets. The MRI reveals interannual variability in juvenile rockfish abundance, a substantial decline in abundance in the 1990s, and a partial recovery in the early 2000s. Predator‐based sampling is a cost‐effective enhancement of scientific net sampling.     

Atypical Aeromonas salmonicida infection in the black rockfish, Sebastes schlegeli Hilgendorf, in Korea

Cultured black rockfish, Sebastes schlegeli, suffered mass mortalities during winter 2008 and spring 2009 in Korea, showing clinical signs of ulcer lesions and haemorrhages over their body surface. The aetiological agent was identified as Aeromonas salmonicida (strains RFAS-1, -2 and -3), which is a non-pigmented, slow-growing bacterium. Phenotypes of RFAS strains showed variation, while 16S rRNA, gyrB, rpoD, dnaJ and recA gene sequences of all the strains were affiliated to A. salmonicida. In particular, vapA gene sequences of the strains were most closely related to one of the five subspecies of A. salmonicida subsp. masoucida (=KCCM 40239(T) ). LD(50) values of RFAS-1 for intraperitoneal and intramuscular injection were 1.5 × 10(5.25) and 1.5 × 10(6.4) cfu/rockfish, respectively. However, A. salmonicida strains KCCM 40239(T) and SAS-1, which originate from masou and chum salmon, respectively, were not pathogenic to black rockfish. RFAS strains, possessing A-layer protein on their surface, exhibited β-haemolytic activity against rockfish erythrocytes and capability to survive in rockfish serum, which seem to be associated with virulence.     

Gonadal lipidomics profile of an ovoviviparity teleost,black rockfish,during gonadal development

Fish Physiology and Biochemistry - In order to study the variation of gonad lipidomics during reproductive cycle, black rockfish was employed as the research model in the present study. Using...     

Measuring the height of the fishing line and its effect on shrimp catch and bycatch in an ocean shrimp (Pandalus jordani) trawl

The relationship between fishing line height (FLH), shrimp catch and bycatch in a semi-pelagic ocean shrimp (Pandalus jordani) trawl was investigated using a newly developed recording inclinometer. The inclinometer was effective at measuring FLH and indicating trawl performance deficits. FLH was determined to be stable during a haul and also between hauls within a given footrope and groundline configuration. FLH was readily adjusted with simple modifications to the footrope “dropper” chains. Inclinometer data showed that FLH can be unequal between double-rigged nets of identical configuration. Shrimp catch and the bycatch of flatfish and juvenile rockfish varied inversely with FLH, suggesting FLH can be adjusted to equalize the catch of shrimp, flatfish and juvenile rockfish between two double-rigged shrimp nets.     

褐菖鲉幼鱼对贻贝养殖生境的利用规律初探

嵊泗海域规模庞大的贻贝养殖生境发挥着养护幼鱼的海洋牧场功能,而探查当地趋礁鱼类在幼体阶段对该生境的利用规律可为当地海洋牧场的设计提供重要参考,为此2018年5—7月对舟山北部枸杞岛贻贝场的褐菖鲉幼鱼、附着生物进行了逐月调查,使用自制网具采集目标生物样品,应用相对密度指数和相关分析法分析了褐菖鲉幼鱼在该生境中的栖息密度、栖息方式和空间分布特征,采用胃含物分析法确定其食性特征,并结合耳石轮纹探究其利用该生境的生长周期。结果显示,褐菖鲉幼鱼的栖息密度时空特征上,5—7月在养殖区贻贝串上的栖息密度分别为(10±6)、(7±5)和(5±5)个/串,时间上呈现逐月递减趋势,随时间的推移养殖区外侧幼体逐渐迁移至内侧近岸区直至消失。栖息方式选择上,褐菖鲉幼鱼栖息数量与贻贝串孔隙大小和附着海藻生物量之间皆呈正相关,但并不显著。饵料利用上,养殖区褐菖鲉幼鱼总体维持较高的摄食强度,各月份平均摄食强度皆高于对照区,主要摄食对象为麦秆虫和钩虾,重量百分比为70.9%和28.3%。栖息周期上,养殖区内褐菖鲉幼鱼耳石平均轮纹数为(57±12)个,其利用养殖贻贝串的周期一般约为2～3月,且该生境中幼鱼耳石纹路间距均匀性和条纹清晰度均明显优于岩礁生境。研究表明,枸杞岛的贻贝养殖生境成为褐菖鲉幼鱼额外的栖息环境,在增殖养护褐菖鲉资源方面发挥了积极作用,因此嵊泗海域在建设海洋牧场时可依据贻贝养殖生境的资源养护原理,通过设置浮体结构强化海洋牧场的饵料场和庇护功能,以提高褐菖鲉种群的补充量,为当地休闲海钓的持续发展提供部分保障。     

High-frequency patterns in abundance of larval Pacific hake, Merluccius productus, and rockfish, Sebastes spp., at a single fixed station off central California

Standard CalCOFI (California Cooperative Oceanic Fisheries Investigations) ichthyoplankton bongo net sampling was conducted every 2 h over 11 days at a single fixed station off central California in February 1995. A conductivity, temperature, and depth cast was completed after each tow to record corresponding hydrographic information. Larval Pacific hake, shortbelly rockfish, and other rockfish were enumerated and length measurements were recorded. Time–depth contours of water density showed a clear boundary, defining the mixed layer along the σ = 25.0 isopycnal, that appeared to fluctuate vertically on a 12‐h cycle centered around 50 m depth. Temperature–salinity plots showed a distinctly different pattern in the mixed layer when compared with water below the pycnocline. Length–frequency distributions plotted by survey day indicated a relatively continuous input of small rockfish larvae into the survey area rather than a resident population growing progressively larger each day. Catches of rockfish larvae were much higher in nighttime tows and varied by survey day, but were unaffected by the depth of the 25.0 isopycnal. In contrast, catches of Pacific hake did not vary significantly on a diel basis, but were significantly variable by survey day and were influenced by the depth of the mixed layer. Catches of Pacific hake larvae were significantly higher during warm‐saline periods (spicy water), while shortbelly rockfish were significantly less abundant under these conditions. Spectral analysis showed a clear 12‐h cycle in the depth of the 25.0 isopycnal and a 24‐h cycle in the catches of rockfish larvae, while Pacific hake catches and spiciness of the mixed layer appeared to have lower frequency cycles in excess of 48 h.     

Effects of different feeding regimes on juvenile black rockfish (Sebastes schlegilii) survival,growth, digestive enzyme activity,body composition and feeding costs

The objective of this study was to establish a proper feeding regime for juvenile black rockfish (Sebastes schlegilii) intended for stock enhancement. We used a combined experimental design to assess the effects of different feeding rates (1%, 3% and 5% body weight per day (BW/day)) and feeding frequencies (apparent satiety or restricted feeding 1 to 3 times daily) on survival, growth, digestive enzyme activity, body composition and feeding costs over 50 days, from newly weaned (initial average weight 1.5 ± 0.2 g) to release size. The results showed that feeding rate significantly affected fish growth, feed utilization and body composition. The highest feed conversion ratio was at 3% BW/day. Increased feeding rates resulted in enhanced growth and higher body lipid content, but this was also accompanied by decreased contents of moisture, protein and ash. With feeding to apparent satiety, increased feeding frequency resulted in higher growth performance and enhanced intestinal lipase activity but decreased gastric protease activity. There were no growth improvements or effects on digestive enzyme activity and body composition with increasing feeding frequency (from one to three times daily) under a fixed‐quantify feeding (3% BW/day). Feed costs increased with increasing feeding rates or apparent satiety feeding frequencies and were associated with shorter growth times to reach a suitable size for release. Our study suggests that a feeding rate of 3% BW/day is the best feeding regime for proper growth and reduced feed costs in juvenile black rockfish before releasing for stock enhancement.     

Effect of dietary cadmium on growth and haematological parameters of juvenile rockfish, Sebastes schlegeli (Hilgendorf)

Experiments were carried out to investigate the growth and haematological parameters in juvenile rockfish, Sebastes schlegeli, exposed to sub‐chronic dietary cadmium (Cd) (0, 0.5, 5, 25, and 125 mg kg^?1) for 60 days. The daily growth rates of weight and length of the rockfish were significantly different from control, and a significant inverse relationship was observed between weight gain and the exposure concentration of dietary Cd at 25 and 125 mg kg^?1 (P<0.05). Glucose in serum was also increased significantly (P<0.05). The concentration of total protein in serum was significantly lower than control at 5, 25, and 125 mg kg^?1. No differences were observed in serum calcium concentration. The magnesium concentration in serum was increased significantly with dietary Cd concentration.     

Genetic Diversity and Population Structure in the Heavily Exploited Korean Rockfish,Sebastes schlegeli,in Korea

The Korean rockfish, Sebastes schlegeli, is a valuable and intensively exploited species in Korea. We discuss the genetic diversity and genetic structure of four Korean rockfish populations using eight microsatellite loci. In total, 161 different alleles from 138 individuals were observed. Average allele number per locus ranged from 2.5 to 23 and allelic richness varied from 13.38 to 14.63 within a population. Despite a long history of stocking practices, we found very high levels of polymorphism (mean heterozygosity = 0.810), which is comparable to other congeneric species. No significant difference in genetic diversity and molecular genetic variance (F_ST and R_ST) was observed among four local samples (P > 0.1). Little indication of contemporary inbreeding (F_IS= 0.051) or population structure (K = 1) was detected. This absence of differentiation may reflect high levels of gene flow along the coast of Korea. Our study demonstrates that rockfish in Korea should be managed as a single unit. Currently, the species does not appear to be genetically threatened, but the potential for a rapid loss of genetic diversity remains. This information on the genetic characteristics of Korean rockfish populations has important implications for fisheries management and conservation efforts, and will aid in the sustainable exploitation of the fishing resources and the preservation of biodiversity.     

气泡幕对许氏平鲉的阻拦效果研究

气泡幕可作为海洋牧场鱼群控制的技术手段之一。本研究通过改变气泡幕在水槽中的相对位置和试验许氏平鲉(Sebastes schlegeli)的密度来观察许氏平鲉的行为反应,运用了观察法、对照试验法和控制变量法探究了气泡幕对不同密度下的许氏平鲉的阻拦效果。结果显示:1)试验鱼20尾时,气泡幕的位置分别设置在矩形水槽长的1/4、1/2和3/4处(鱼的密度为12.52、6.26、4.17尾/m2),阻拦率分别达到了98.2%、88.4%和92.9%,阻拦效果明显。2)气泡幕设置在水槽长度方向的1/2处,试验鱼分别为5尾、10尾、15尾和20尾时,气泡幕阻拦率分别达到了100%、85.7%、100%和88.4%(鱼群密度分别为1.56、3.12、4.69、6.26尾/m2),阻拦效果良好。3)由于阻拦率较高,试验鱼群密度和阻拦效率没有明显的关系。本研究结果可为我国投放许氏平鲉的海洋牧场鱼群控制技术以及取水口拦鱼技术提供参考。     

Attractiveness of various protein sources to juvenile rockfish (Sebastes schlegeli,Hilgendorf 1880)

ABSTRACT

The attractiveness of various protein sources of 16 feed ingredients was determined in juvenile rockfish (Sebastes schlegeli) by using reinforced acrylic tank composed of three equally divided rectangular attracting chambers and an acclimatization chamber. Thirty fish were held in the acclimatization chamber at a time and tournament comparison of feed ingredients was applied to evaluate attractiveness. Jack mackerel (JM) (40.0%), sardine (SM) (33.3%), Pollack (PM) (40.0%), shrimp (SHM) (36.7%), mussel meal (40.0%) and oyster (43.3%) meals achieved the highest feeding attractiveness to rockfish in the 1^st through 6^th preliminary test, respectively. JM (40.0%), SHM (36.7%), squid meal (SQM) (33.3%), SM (40.3%), PM (40.0%) and PM (36.7%) achieved the highest feeding attractiveness to fish in the 7^th through 12^th preliminary test, respectively. Among the top five feed ingredients showing high attractiveness to rockfish, JM achieved higher attractiveness than PM and SHM in the 1^st trial. In the 2^nd trial, attractiveness of JM to rockfish was higher than SM and SQM. SM achieved higher attractiveness to rockfish than SQM, but not different from PM throughout the 30-min observation in the 3^rd trial. The strongest feeding attractant response of rockfish was observed in JM, followed by SM, SQM, PM, and SHM, in order among various feed ingredients.