Spawning grounds and reproductive traits of anadromous and resident pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan

SUMMARY: The objective of this study was to reveal the spawning grounds and reproductive characteristics of anadromous and resident pond smelt, Hypomesus nipponensis , coexisting in Lake Ogawara. Life history styles of females shedding in spawning grounds in the lake and its inflowing rivers were differentiated by otolith increment analysis. Size, dry weight, and water content of mature oocytes and fecundity of fish were compared between resident and anadromous fish. Both anadromous and resident fish spawned in the lake. In contrast, no resident fish were found in any of the inflowing rivers, where only anadromous fish spawned. Regression of fecundity against standard length was discontinuous with an inflection point at 63.8 mm, which is the body size that differentiates large anadromous spawning groups from small resident spawning groups. Mean oocyte diameters were not significantly different between resident and anadromous fish. The eggs of resident fish had significantly more water content and a significantly lower dry weight than those of anadromous fish. These differences might influence the growth and developmental processes of progeny.     

洞庭湖花■的年龄、生长和资源评估

根据2017-2019年在洞庭湖采集的228尾花[鱼骨](Hemibarbus maculatus)样本,使用耳石和鳞片研究其年龄、生长和资源现状。结果显示:耳石和鳞片是良好的年龄鉴定材料,鳞片上年轮特征以普通切割型为主,耳石重量可用于粗略、快速年龄鉴定。样本体长90~262 mm,优势体长组120~180 mm;体重11.0~399.0 g,优势体重组为20.0~80.0 g;年龄组成1~4龄,1龄为优势年龄组。体长体重关系:W=7.434×10^-6 L s 3.165,b值显著大于3,为异速生长鱼类。Von Bertalanffy生长方程:L t=301.4[1-e-0.471(t+0.341)],W t=522.0[1-e-0.471(t+0.341)]3.165,拐点年龄2.11龄(体长206.2 mm,体重156.9 g)。花[鱼骨]为典型的r-选择鱼类,总死亡系数3.321,自然死亡系数0.823,开发率为0.752,种群处于过度开发状态。建议起捕体长为172.2 mm,开发率降至0.601,同时在繁殖季节设置人工鱼巢,以恢复洞庭湖花[鱼骨]种群资源。     

Effect of marine Eubothrium sp. (Cestoda: Pseudophyllidea) on the growth of Atlantic salmon, Salmo salar L.

Atlantic Salmon, Salmo salar L., experimentally infected with marine Eubothrium sp. were kept together with uninfected salmon in the laboratory for 11 months in two tanks, 80 infected and 80 uninfected in each tank. The infected fish had a reduced growth rate compared with the uninfected fish. Significant differences in growth between infected and uninfected fish were not observed until several months post-infection. There was no correlation between the number of Eubothrium sp. and fish weight, indicating that even low intensity alters the growth rate of the salmon. The cestode had the same effect on both sexes of salmon. Haematocrit level was found to be significantly lower in infected compared with uninfected salmon in one of the samples during the experiment.     

The differential effects of Ligula intestinalis (L.) plerocercoids on host growth in three natural populations of roach, Rutilus rutilus (L.)

Abstract – This study reports the differential effect of the pseudophyllidean cestode, Ligula intestinalis , on the growth rates of three fish populations of the roach, Rutilus rutilus , under field conditions. Here, we show that only one host-population is affected by parasite-induced gigantism in the first 2 years of host life. Paradoxically, this increase in fish growth is strongly correlated with the parasitic load in plerocercoid stages, in that only the roach population subjected to the heaviest parasitic pressure shows an enhanced growth of cestode-parasitized individuals. This host gigantism observed in only one locality is associated with parasite-induced fish mortality occurring, on average, one year earlier in this fish population when compared to other populations. We discuss the different reasons for this differential parasite effect on growth enhancement across host-population in natural settings. Whether the growth effects represent an adaptive response by the host or a manipulation by L. intestinalis of the host, remains to be elucidated.     

Use of a vertical-slot fishway by galaxiids in Western Australia

Abstract –  The Goodga River Fishway is the first vertical-slot fishway in Western Australia and was opened in April 2003 with the aim of increasing the habitat available to two galaxiids; the trout minnow ( Galaxias truttaceus ), a highly restricted freshwater fish species in Western Australia, and the widespread common jollytail ( Galaxias maculatus ). The fishway was designed to function during low flows to coincide with the upstream spawning migration of G. truttaceus . Prior to the opening of the fishway, no fish were found above the Goodga River gauging station (weir), which is approximately 2 km upstream of the river's entrance to Moates Lake. Fish migrations were monitored in each season between April 2003 and February 2005. Galaxias truttaceus utilised the fishway in all sampling periods. Adult fish migrated up the fishway prior to spawning, while large numbers of new recruits (small juveniles) negotiated the fishway during November 2003 and 2004. More G. truttaceus and G. maculatus were captured on the fishway during daylight hours compared with the night; however, larger G. truttaceus were more commonly captured at night whereas G. maculatus on the fishway were larger during the day. The fact that fishway utilisation by G. maculatus was consistent during all samples and new recruits migrated during periods of low flow demonstrates the importance of understanding the migration patterns of the target species when designing fishways.     

人工养殖湖泊花(鱼骨)卵巢周年变化与性成熟年龄的研究

对花(鱼骨)作组织学研究表明,人工养殖湖泊中花(鱼骨)的卵巢发育可划分为六期,花(鱼骨)的性成熟年龄为一冬龄。     

Content of synthetic astaxanthin in escaped farmed Atlantic salmon, Salmo salar L., ascending Norwegian rivers

Abstract  Isomeric ratios of astaxanthin in eggs and alevins of Atlantic salmon, Salmo salar L., have proven useful in identifying female spawners of farmed origin, but the method underestimates the proportion of fish of farmed origin. The rate of underestimation was studied by analysing astaxanthin content in tissue of 55 farmed Atlantic salmon ascending two Norwegian rivers in the autumn of 1991. The astaxanthin content fell into two distinct classes. Fifty-one per cent of the adult escaped salmon had isomeric ratios similar to salmon fed synthetic astaxanthin, whereas all the remaining fish had ratios similar to wild fish. Discriminant analysis classified 96.4% of the fish with known astaxanthin content into the correct astaxanthin class on basis of tail-fin erosion, length, weight and gill-cover damage. This discriminant function was used to estimate the astaxanthin classification of 1017 farmed salmon caught in nine rivers during 1989–1991. The classification success varied among years from 52 to 64%. Corresponding numbers for females and males were 45–48% and 54–70%, respectively. Thus, estimates of spawning rates of farmed female salmon via astaxanthin content in eggs or alevins from redds should be adjusted accordingly. The observed isomeric ratios of astaxanthin in the escaped farmed salmon and the relationship with morphology indicates that a significant proportion of the escapees ascending rivers have spent more than 1 year in the wild after escape.     

Analysis of growth, weight and relevant indices of diploid and triploid population of tench Tinca tinca (Linnaeus 1758)

This study determined biometric and weight parameters and relevant indices of diploid and triploid tench. Altogether, 137 siblings of tench were studied. The effect of ploidy level appeared in significantly better growth of triploids (P<0.001) as to biometric [total length (TL), standard length (SL), body height (BH), body width (BW)] and weight [fish weight (FW), carcass weight (CW)] parameters of T₃ of both sexes and of T₃₊ females. The effect of ploidy level also appeared as significantly higher dressing percentage (DP; P<0.001) of triploid T₃ females compared with other groups, significantly higher gonad weight (GW) and gonadosomatic index (GSI; P<0.001) of diploid T₃ females, as well as GSI and hepatosomatic index of diploid T₃₊ females. The effect of sex appeared in significantly higher (P<0.001) biometric (TL, SL, BH, BW) and weight (FW, CW) parameters of T₃ females of both ploidy levels, as well as of triploid T₃₊ females. The effect of sex also appeared as significantly higher DP (P<0.001) of males in diploid T₃ fish, as well as of males of both ploidy levels in T₃₊ fish and significantly higher GW and GSI (P<0.001) of females in diploid T₃ fish, as well as of females of both ploidy levels in T₃₊ fish. This study shows evidence for faster somatic growth and bigger final weight of triploid populations of tench compared with diploids in both age categories T₃ and T₃₊.     

Coastal movement and growth of domesticated rainbow trout (Oncorhynchus mykiss (Walbaum)) in Norway

Between 1979 and 1991, hatchery-reared 1+ and 2+ rainbow trout were released in May and June in the Boknafjord at the mouth of the River Imsa, and from April to June in the Oslofjord, southern Norway. The fish were recaptured in the fjords of release, in rivers emptying there and from rivers and sea further along the Norwegian coast. Of the total recaptures, 35.6% ascended rivers in the year of release. Some fish released at the River Imsa returned to the area of release after spending 1 to 3 years at sea. Among those that were recaptured in rivers, 11.9% were recaptured in other rivers than the Imsa. The growth rate of the fish varied inversely with size at release. The growth rate was higher in the Oslofjord than in the Boknafjord, and in both areas the growth rate decreased with time after release. Rainbow trout that had escaped from local fish farms entered the River Imsa between March and December. Adults ascending in spring remained a shorter time in the river (37 days) than those ascending in autumn (200 days). Fish entering in autumn decreased more in weight during their river stay than those ascending in spring, and females more than males. Spawning took place in April-May. The monthly mean river stay of juvenile entrants ranged from 2 weeks to 6 months. In total, 27.8% of the rainbow trout escaped from fish farms and captured in the Imsa strayed to other rivers for repeat spawning. There is no evidence for continuing survival of escaped Norwegian rainbow trout in the wild.     

Sphaerospora testicularis sp. nov. (Myxosporea: Sphaerosporidae) in wild and cultured sea bass, Dicentrarchus labrax (L.), from the Spanish Mediterranean area

Abstract. A new myxosporean, Sphaerospora testicularis sp. nov., was found in fresh smears from the organs of wild and cultured sea bass, Dicentrarchus labrax (L.), and seminal fluid from spermiating cultured males. It is distinguished from all previously reported Sphaerospora spp, by the shape and dimensions of the mature spore, its location and the host and its geographical distribution. Only males were parasitized; 2.5% of the wild fish and 6-25% of the cultured fish were infected. In spermiating cultured males, the prevalence of infection increased progressively from 6-9 to 75% during the study period. The parasite causes destruction of the tubular tissue of testes and a reduction or loss of spermatozoa.     

黄河三角洲水质污染对淡水鱼类多样性的影响

1993-1997年对黄河三角洲8条河流、3个水库和1个湖泊水质连续5年进行了监测，1996-1997年对淡水鱼类多样性开展了同步系统调查，水质评价结果：6条河流为重污染，2条河流为严重污染，2个水库轻污染，麻大湖严重污染，淡水鱼类共鉴定出102种和亚种，隶属于9目17科65属，占山东省炎水鱼类总种数的89%。水质污染已志致鱼类多样性减低，少数河流鱼类绝迹。     

Reproduction of the North American blackbass, Micropterus salmoides (Lacepède), in an equatorial lake, Lake Naivasha, Kenya

Abstract. In contrast to its North American relatives, the Lake Naivasha blackbass, Micropterus saimoides (Lacepdde) has a prolonged spawning season of 8 months between June and January, peaking in August to November. This season is characterized by the presence of high numbers of mature fish with the highest gonadosomatic index (GSI). Analysis of GSI variations in different length-classes reveals that maximum reproduction occurs in the 30-34.9-cm length-class in males and 40-44.9-cm in females. Analysis of the GSI values in the different sampling stations identifies two stations as the breeding areas of M. salmoides in the lake.
The positive correlation between the GSI and the stomach fullness index suggests that the species probably feeds all year round, including the spawning season. Fifty per cent of males and females are mature at 25-29.9-cm and 30-34.9-cm length-classes respectively. The fecundity of fish of 28.4 cm (371 g) to 33 cm (550g) ranged from 1300 to 3524 with a mean of 2203 eggs. Fecundity had no relationship with body length but increased linearly with body weight.     

Different growth and processing traits in males and females of European catfish,Silurus glanis

Two experiments were developed in France to assess whether growth and processing traits differ for males and females in the European catfish, Silurus glanis. In the first experiment, fish were raised from 5 to 200 g in a pond for 7 months. A significant sex effect is demonstrated in males for live weight at the end of the experiment (males 147.5±5.4 g vs females 132.9±4.9 g) and head index (males 20.6±0.1 % vs females 21.2±0.1 %, P < 0.05). In the second experiment, fish were raised from 885±196 g to 2 266±418 g in a recirculated system at 20.7±1.4 °C for 120 days. A differential growth between the sexes is also registered. Males are heavier and longer (+ 357 g or + 17.0 % and + 6.2 % in length at day 120) and present a higher gutted weight and yield (+ 367 g or + 18.7 %; 95.0±0.9 % vs 93.8±1.8 %) and fillet weight (+ 233 g or + 20.9 %) than females after slaughter.     

Effects of Dietary Protein Levels on Gonad Maturation, Size and Age at First Maturity, Fecundity and Growth of Nile Tilapia

Six-week-old Nile tilapia (Oreochromis niloticus) fry with an average weight (SD) of 0.51(0.2) g were reared for 140 days on five formulated, isocaloric diets of different protein levels (25, 30, 40 and 45% by dry weight). Fish fed diets of higher protein levels (40 and 45%) showed better growth and feed conversion ratio than those on lower protein levels. Fast-growing fish matured earlier. Maturation rate was affected by the dietary protein levels. Males matured earlier than females: the first mature males were recorded when they were 14 weeks old, whereas the females matured after 18 weeks. In both sexes, mean percentage of mature fish rose with increasing dietary protein level, the percentage of mature males being higher than that of the females. Similarly, the percentage of mature fish rose with the increasing age of fish, with more than 50% males and females mature at the age of 22 and 24 weeks, respectively, the exception being the 25% protein diet fed fish, where the percentage of mature fish was below 50%. In all treatments, spawning was initiated when the fish were 22 weeks old. Smallest size at spawning of males and females was 9.2 cm (13.1 g) and 8.1 cm (8.9 g), respectively, and dietary protein levels influenced the size of fish at first maturity. For both sexes, no difference was found in the gonado-somatic index (GSI) among different treatments. Fecundity increased with increasing dietary protein levels, but significant differences were found only between 40–45% and 25–35% dietary protein levels. The relative fecundity (eggs g^–1 female) was higher at the lower dietary protein levels (25–35%) than at the higher dietary protein levels (40–45%). The dietary protein levels did not have any significant influence on the size and weight of mature eggs. The chemical composition of fish and mature ovaries was significantly influenced by the dietary protein level.     

Density effects on length at maturity of walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> off the pacific coast of northern Japan in the 1990s

To determine how stock abundance fluctuations of walleye pollock Theragra chalcogramma are related to variations in reproductive characteristics, the length at 50% maturity of the fish sampled off the Pacific coast of northern Japan from 1990 to 1999 was examined. In both sexes, the fish density increased, and the body length of age-3-5 fish decreased, but the condition factor and the age at 50% maturity showed no clear trend during this period. Male length at 50% maturity decreased, while value for females showed no clear trend. In both sexes, significant negative correlations were found between density index (combined age-3-5) and each body length at age-3-5. Significant positive correlations were seen between each body length at age-3-5 and length at 50% maturity in males. Positive correlation between body length at age-5 and length at 50% maturity was significant in females from 1990 to 1999, except for the samples in 1998. We suggest that the fish density might affect the length at maturity in males and possibly also in females.     

青海省土著鱼类名录

本报道青海省境分布土鱼类49种,分3目5科18属。这些鱼类中以鲤形目为主,有44种和亚种,占全部鱼类总数的89．8％,鲑形目1种,鲇形目4种。     

Lutein enrichment of the rotifer Brachionus sp. using freeze‐dried Muriellopsis sp. cells

Rotifers, used in aquaculture as feed for early larval stages, are poor in carotenoids compared with copepods, the natural most common prey item of marine fish larvae. A minimal sufficient level of carotenoids in fish larvae may be essential for a correct development. The freshwater microalga Muriellopsis sp. has been identified as a potential source of the carotenoid lutein with possible application in aquaculture. Lutein is a potent antioxidant, with potentially beneficial effects as a carotenoid for fish larvae. This study describes the lutein enrichment of the rotifer Brachionus sp. when incubated with homogeneously dispersed suspensions of freeze‐dried, lutein‐rich Muriellopsis sp. in seawater. A short enrichment time (2 or 2.5 h) resulted in a higher lutein content of the rotifers than a long enrichment time (13.5 or 24 h). Although the concentration of lutein in enriched rotifers, 0.06–0.16 mg (g dry weight)^?1 was low compared with its content in Muriellopsis sp. [about 3 mg (g dry weight)^?1], it was in the range reported for natural copepod populations. Therefore, we conclude that freeze‐dried biomass of Muriellopsis sp. can be used to enrich rotifers with lutein, providing an adequate level of this carotenoid for marine fish larvae.     

花幼鱼饲料中脂肪水平适宜量的研究

以等量混合的鱼油、豆油作为添加的脂肪源,设计成脂肪水平为1.62%、3.71%、5.77%、7.96%、9.95%和12.01%的6种饲料进行60 d养殖对比试验研究了饲料中花(Hem ibarbus maculatus)幼鱼脂肪水平适宜量。结果显示:花幼鱼饲料中不同脂肪水平对花的相对增重率、饲料系数和蛋白质效率存在显著差异(P<0.05),其中以投喂脂肪水平为7.96%的饲料花的生长最快,相对增重率为(1066.35±13.15)%;以投喂脂肪水平为5.77%的饲料花对蛋白质利用最高,蛋白质效率为(1.84±0.10);以投喂脂肪水平为5.77%的饲料花对饲料的利用最好,饲料系数仅1.39。研究结果表明:花幼鱼饲料中脂肪含量以5.77%~7.96%为最佳,考虑到饲料成本,把花幼鱼饲料脂肪的最适含量定为6%~7%。     

Annual sex hormonal profiles, gonad development and age determination of the Mekong giant catfish (Pangasianodon gigas, Chevey)

Annual sex hormonal profiles, gonad development and age determination of 18 (13–14 kg body weight) and three (145–226 kg body weight) Mekong giant catfish (MGC) (Pangasianodon gigas, Chevey) reared in earthen ponds in Chiang Mai and from the Mekong River in Chiang Rai, Thailand, respectively, were investigated. The hormonal profiles were determined from blood samples of the fish by electrochemiluminescence immunoassay during May to August in 2000. The highest testosterone levels of 0.06 ng mL^?1 in both sexes and the highest oestradiol of 47.8 and 14.23 pg mL^?1 in females and males, respectively, were observed in May. The gonadosomatic index was found to be 0.07 for males and 0.38 for females from ponds in comparison with 2.27 for males and 8.29 for females from the Mekong River. Higher development stages of spermatocytes and oocytes of the cultured fish in May than in February and November were demonstrated. No mature germ cells were obtained from either the males or females, indicating no sexual maturity. The average age of fish was determined from the annual rings of the cross‐section of the pectoral fins by a stereomicroscope. The average age of fish in earthen pond determined from the annual ring was 8 years, which agreed with the actual culture records, while those from the Mekong River were 21 years. This information will be beneficial for the breeding programmes and conservation of the MGC.     

The effect of Eimeria sp. infection on the condition of blue whiting, Micromesistius poutassou (Risso)

Abstract. Eimeria sp. infection of blue whiting, Micromesistius poutassou (Risso), taken to the north and west of Scotland, was investigated with particular reference to the effect on host condition. Eimeria sp. is a parasite of the liver parenchyma and causes extensive lesions. Juvenile blue whiting were not found to be infected before the late 1-group stage, but all 308 adult (3- to 17-group) fish examined were infected. Condition factor ( k = 100 w/l³ ) showed a statistically significant decrease with increasing intensity of infection. Average value of liver weight, expressed as a percentage of total body weight, also decreased with increasing intensity of infection. It is concluded that Eimeria sp. infection is a major factor contributing to loss of condition in blue whiting from the study area. The loss of weight in fish with moderate-to-heavy infections was estimated at from 6 to 10%; this figure does not take account of mortalities resulting from Eimeria infection nor does it take account of the most heavily infected fish which could not be included in the analysis because sufficiently accurate estimates of the large numbers of oocysts present were not made.