Dionchus postoncomiracidia (Monogenea: Dionchidae) from the skin of blacktip sharks, Carcharhinus limbatus (Carcharhinidae)

Postoncomiracidia of Dionchus sp. are described from specimens collected from the skin of 2 blacktip sharks Carcharhinus limbatus, captured in the northern Gulf of Mexico. The parasites resemble nonciliated oncomiracidia hatched from eggs laid by Dionchus sp. on gills of a cobia Rachycentron canadum and adults of Dionchus remorae that were collected from gills of a common sharksucker Echeneis naucrates, captured in association with a third blacktip shark. The hamuli of the postoncomiracidia were morphologically similar to those of adult D. remorae. This is the first report of dionchids from an elasmobranch and from a location other than the gills. These findings support the idea that some dionchid oncomiracidia colonize the skin of sharks or other aquatic vertebrates that sponsor remoras, prior to transferring to other remoras and maturing.     

Species and size compositions and reproductive biology of rays (Chondrichthyes, Batoidea) caught in target and non-target fisheries in eastern Indonesia

Extensive surveys of various fish landing sites in eastern Indonesia, conducted between April 2001 and March 2006, recorded a total of 54 species of batoid rays belonging to 12 families. The Dasyatidae was by far the most speciose family, comprising half of the recorded species, and was also the most abundant, contributing 89 and 44% to the total numbers and total estimated biomass of batoids, respectively. The size and sex compositions of 23 species of rays are described and an accurate size at maturity of males, i.e. with 95% CI, was determined for 13 of these species. The sex ratios were found to be close to parity in the majority of species, however, the landings of the whitespotted guitarfish Rhynchobatus australiae consisted of significantly more females than males, a situation also recorded for this species in the by-catch of the northern Australian prawn fishery. Data on aspects of the reproductive biology of three dasyatid species ( Dasyatis cf. kuhlii , Dasyatis zugei and Himantura walga ), which form a substantial component of the by-catch of the bottom trawl fisheries in the region, were collected on most sampling occasions. These small rays, i.e. maximum sizes 243–379 mm disc width, were found to have no distinct seasonal reproductive cycle and small litter sizes, i.e. less than four embryos. Opportunistic reproductive data, e.g. litter size and embryo sizes, were also collected from various other species. The litter sizes of the rhynchobatid and rhinobatid species examined were found to be larger than those of the gymnurid and dasyatid species examined, i.e. seven to 19 and two to 13 v. one to four, respectively. The data presented in this paper for the numerous species of rays which are landed by target and non-target fisheries in Indonesia represent the first such data for the vast majority of these species.     

Ecological niche models reveal the potential zones of invasion of the cobia (Rachycentron canadum) in the Eastern Pacific Ocean

Hydrobiologia - Cobias (Rachycentron canadum) are large fish that live in all the tropical oceans of the world, except for the Eastern Pacific Ocean (EPO). During 2015, a cobia cage culture was...     

饲料中不同水平鱼蛋白水解物对军曹鱼稚鱼生长及体组成的影响

设计4种等能等氮试验饲料,对照组以鱼粉为单一蛋白源,处理组分别以鱼蛋白水解物替代鱼粉蛋白的17%、34%和51%,军曹鱼(Rachycentron canadum)稚鱼的初始重为(3.79±0.22)g,实验在室内流水养殖系统中进行6周的饲养试验,每种饲料随机3个重复。试验结果显示不同水平鱼蛋白水解物对试验鱼的存活率没有显著影响(P>0.05),除了以鱼蛋白水解物替代鱼粉蛋白51%组外,其他各组的增重率(WG)和饲料摄入量(FI)都是随着饲料中鱼蛋白水解物替代鱼粉蛋白量的增加而增加。试验结果表明,在军曹鱼稚鱼饲料中用鱼蛋白水解物替代34%的鱼粉蛋白对于军曹鱼稚鱼的生长和饲料摄入量具有一定的促进作用。军曹鱼稚鱼血浆中胆固醇含量随着饲料中鱼蛋白水解物添加水平的升高而升高,而血浆中的总蛋白含量则无此规律,各处理组血浆中的甘油三酯无显著差异(P0.05)。       

Seasonal variation in abundance of the Indian mackerel,Rastrelliger kanagurta Cuvier (Pisces: Scombridae) along the Zanzibar coast of East Africa

Purse-seine catches of the mackerel, Rastrelliger kanagurta Cuvier along the west coast of Zanzibar revealed seasonal patterns of abundance associated with monsoon winds. Low catches were obtained during the south-east monsoons while the north east monsoons were characterised by high catches. The largest sizes of mackerel were caught between June and August with a mixture of large and smaller ones between September and March. Mackerel in spawning condition were common between June and September with immature ones between September and January. The variations in mackerel abundance, size composition, and maturity of the fish are discussed in relation to seasonal changes, fish migrations, recruitment and food supply.     

The reproduction ofBlennius pavo (Teleostei,Blenniidae). I. Ovarial cycle,environmental factors and feeding

Blennius (Salaria) pavo is a very common coastal fish in the Mediterranean Sea. The development of the ovary was studied over a period of one year; seven stages of oogenesis are described. Ripe eggs are carried during the spawning season from Juni to August. The ovary shows a resting period of more than half a year (September to March). Environmental factors of the study area such as surface water temperature and daylength are described as well as the condition factors of male and female fish. Observations on food and behaviour during the winter months are also included.     

Reproductive cycles in a reared strain of the mummichog, a daily spawner

Annual, lunar, and diel samplings were taken from a strain of mummichog (Arasaki strain) reared in outdoor tanks under natural conditions, to examine gonadal maturity. Gonads of yearling fish were quite immature in September. During late autumn and winter, a gradual increase in the GSI of both sexes was observed, and the growth of cortical alveolus phase oocytes in females and basal spermatogenesis in males progressed. In late February, a rapid increase in the GSI of both sexes, vitellogenesis in females, and active spermatogenesis in males, occurred. The spawning period of the yearling fish was from late March to August judging from the presence of milt-producing males and ovulated females. The spawning period of the underyearling fish started in the same month as the yearlings, but terminated 1 month earlier. Plasma levels of oestradiol-17 β (E₂) in females and testosterone in males were high during the spawning period in the yearlings. In the underyearlings, however, E₂ levels peaked in early spring, and declined in the latter part of the spawning period. Neither a lunar nor semilunar cycle was evident in the reproductive activity of this fish, which proved to be a typical daily spawner. Females showed an apparent daily reproductive cycle; oocyte maturation commenced at about 1200 hours, germinal vesicle breakdown (GVBD) occurred at about 2400 hours, and ovulation was completed by 2400 hours, 24 h after GVBD. Such clear annual and daily reproductive cycles make this strain of mummichog a suitable model for the study of environmental and endocrine regulation of reproductive cycles in marine and estuarine teleosts.     

闽南-台湾浅滩渔场二长棘鲷群体集群行为宏观量化与分析

根据1998年7月到2000年6月闽南-台湾浅滩渔场开展二长棘鲷资源的专项调查资料, 计算出闽南-台湾浅滩渔场二长棘鲷的各月E值, 定量分析其集群行为变化规律。结果表明: 闽南-台湾浅滩二长棘鲷全年月平均E为7.4409108J, 生殖期间12月到翌年3月, 其月平均E 2.4949108J, 是全年月平均E的0.34倍, 鱼群集中; 4-5月, 幼鱼大量出现, 月平均E为4.556108J, 是全年月平均 的0.61倍, 鱼群相对集中; 主要索饵季节6-8月, 月平均E为1.3448109J, 是全年月平均 的1.81倍, 鱼群分散; 9-11月, E分别为1.435109、9.7409108、5.769108J, 分别是全年月平均 的1.93、1.31、0.78倍, 鱼群为适应水温和寻找产卵场, 在外移过程中逐渐集中。可见, 闽南-台湾浅滩二长棘鲷的生殖群体集群性最强, 其次是幼鱼群体、以适应水温和寻找产卵场为目的的群体, 而索饵群体分散。       

Annual movement and migration of adult pikeperch in a lowland river

The downstream migration of 46–66 cm radio-tagged adult pikeperch Stizostedion lucioperca , in the River Gudenaa, Denmark, from late September to late December, coincided with a reduction in the frequent occurrence of prey fish in the tagging area, and hence was interpreted as a feeding migration. The upstream migration from March to mid-April in spring took place prior to spawning which occurred from late April to June.     

Morphology of ovarian changes during the reproductive cycle of the fish, Mystus tengara (Ham.).

A study has been made of the morphological and histological changes of the cat fish (Mystus tengara) ovary during its reproductive cycle in natural and confined waters. This fish is oviparous and breeds once a year during the rainy season (July throught September). Factors responsible for bringing about spawning in fishes are discussed and the onset of spawning in Mystus is attributed to monsoon rains. In the ovarian cycle 7 phases have been recognised, whic are based on the gross morphological changes in the ovary, the percentage and duration of different developmental stages of oocytes, the average diameter and the gonosmatic index. They are: 1) immature virgin (November-February); 2) preparatory virgin (March-April); 3) maturing virgin (April-May); 4) pre-spawning virgin (June); 5) spawning (July-August); 6) depletion (September), and 7) recoupment (October-November). Oocyte growth has been divided into 9 stages. The ova diameter and gonosomatic index are maximum in July and minimum in November and December.     

Foraging behaviour and prey discrimination in the bluespotted maskray Dasyatis kuhlii

A study observing the foraging behaviours and prey discrimination of a common demersal stingray, the bluespotted maskray Dasyatis kuhlii was performed under controlled laboratory conditions. A selection of prey species and masses were offered at depths of 10 and 50 mm in sand. Foraging efficiency and prey selection at both burial depths were compared. Dasyatis kuhlii selected the ghost shrimps, Trypaea australiensis and T. australiensis >2·5 g, range ± 0·2 g though foraging errors represented by prey being excavated and not consumed suggested a limited discriminatory ability at the point of detection. Burial depth did not influence prey species, mass selection or discriminatory ability.     

The link between migration, the reproductive cycle and condition of Sardinella aurita off Mauritania, north-west Africa

The annual migration pattern of round sardinella Sardinella aurita up and down the north-western African coast between 12° N (Senegal) and 22° N (western Sahara) was shown to be associated with spawning activity and a distinct seasonality in fish condition, based on monthly sampling from commercial catches (2000–2003). Some S. aurita were found to spawn throughout the entire year, but a peak in spawning existed during the summer (June to September). The spawning cycle is apparent from seasonality in maturity stages, but is also demonstrated by the increase in gonad mass and fat content of the fish in springtime, the period preceding spawning. During the months after spawning, although feeding is maintained, the physical condition of the fish collapses, and fat content rapidly declines.     

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario

This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development. This revised version was published online in August 2006 with corrections to the Cover Date.     

The seasonal changes in somatic energy content of Gulf of Alaska yellowfin sole, Pleuronectes asper

Seasonal measurement of body energy content was made for Pleuronectes asper (Pallas, 1814) from the Gulf of Alaska. Whole body energy content of complete fish (～ 3472 J g^?1 wet wt) was minimal in May for females as their overwintering phase ended, then increased to ～ 4456 J g^?1 prior to spawning. The ovarian index [(g.w./t.w.) × 100] and energy content of ovaries (J g^?1) was highest in June and May respectively, and then declined markedly by August as spawning occurred. Throughout the year male whole body energy content of complete fish ranged from 3351 to 4590 J g^?1 with the lowest values in May and highest values occurring during June to September, the feeding season. The testes index [(g.w./t.w.) × 100] and total energy content of testes (J g^?1) were high in March and lowest during June and July. On a weight-specific basis, males and females had similar whole body energy values throughout the year. Juveniles followed the same seasonal trends in energy storage as adults and had similar whole body energy values. Whole body energy content was linearly related to wet and dry weight condition factor with r² values of 0.70 and 0.87, respectively. Dry body weight as percent of wet body weight was the best predictor of body energy (r²=0.91). Yellowfin sole had an annual energy cycle with energy accumulation and growth from May to September. Thereafter they utilized stored energy for metabolic and reproductive needs. Spawning began in late May or early June and fish were spent by August. Whole body energy content increased by 28, 33 and 35% between May and June, for females, juveniles, and males, respectively, the most dramatic change during the year long survey. This suggests that intense feeding in May must be an important aspect of their energy storage cycle.     

Spawning behaviour of barred spiny eel,Macrognathus pancalus,in the River Gomti,India

The present study investigated the spawning behaviour of the spiny eel, Macrognathus pancalus, and its relationship with the environment (photoperiod and temperature). The results show that M. pancalus breeds during February to September with peak spawning during February/March and July/August, indicating two main breeding periods. Initiation of breeding occurs during increasing day lengths in early spring (February/March), and regression during decreasing day lengths in autumn (September/October). The breeding status confirmed by gonadosomatic index (GSI) and ovarian histology showed six stages of ovarian maturation (viz. stage I: chromatin nucleaolar; II: perinucleolar; III: cortical alveolar; IV: vitellogenesis; V: ripe; and VI: partially spent), with predominance of one or more stages at a particular time of the year. Males also followed a similar seasonal pattern in gonadal maturation as reflected by their GSI. Results show that M. pancalus is a seasonal breeder with bimodal spawning activity. The breeding pattern suggests an influence of prevailing day length conditions at this latitude.     

Melatonin in the Regulation of Annual Testicular Events in Carp Catla catla: Evidence from the Studies on the Effects of Exogenous Melatonin,Continuous Light,and Continuous Darkness

The physiological significance of melatonin in the regulation of annual testicular events in a major carp Catla catla was evaluated through studies on the effects of graded dose (25, 50, or 100 µg/100 g body wt.) of melatonin exogenously administered for different durations (1, 15, or 30 days) and manipulation of the endogenous melatonin system by exposing the fish to constant darkness (DD) or constant light (LL) for 30 days. An identical experimental schedule was followed during the preparatory (February–March), pre‐spawning (April–May), spawning (July–August), and post‐spawning (September–October) phases of the annual cycle. Irrespective of the reproductive status of the carp, LL suppressed while DD increased the mid‐day and mid‐night values of melatonin compared to respective controls. Influences of exogenous melatonin varied in relation to the dose and duration of treatment and the reproductive status of the carp. However, testicular response to exogenous melatonin (at 100 µg, for 30 days) and DD in each reproductive phase was almost identical. Notably, precocious testicular maturation occurred in both DD and melatonin‐injected fish during the preparatory phase and in LL carps during the pre‐spawning phase. In contrast, testicular functions in both the melatonin‐treated and DD fish were inhibited during the pre–spawning and spawning phases, while the testes did not respond to any treatment during the post‐spawning phase. In conclusion, this study provided the first experimental evidence that melatonin plays a significant role in the regulation of annual testicular events in a sub‐tropical surface‐dwelling carp Catla catla, but the influence of this pineal hormone on the seasonal activity of testis varies in relation to the reproductive status of the concerned fish.     

Studies on the biology of some freshwater fishes Part VI. Mystus cavasius (Ham.)

Summary The biology of a freshwater fish, M. cavasius with particular reference to its length frequency, breeding and food has been described. length frequency distribution gave an indication of 4 modes during the quarter, July–September.Both the sexes attain maturity when they are approximately 10 cm long. Females grow larger than the males and are more abundant in the population. The spawning of this fish seems to take place during August and September. Maturing ovaries of females show only one batch of eggs which is probably shed in a single spawning act. The condition factor of the fish has no correlation either with the seasonal changes in maturity or with the feeding rhythm. The fish has an omnivorous habit and consumes all types of food available in the habitat. The feeding is high during the monsoon and winter months and low during the summer months.This work was carried out in the Department of Zoology, Aligarh Muslim University, Aligarh, U.P. India in continuation of the series I–III by Qasim & Qasim (1964) and IV–V published elsewhere by the present author (1970–71).     

青菱湖中长春鳊生物学的研究

1983-1985年对通长江的青菱湖中长春鳊的年龄与生长、食性、繁殖及其鱼群江湖交流等生态习性进行了调查。发现相当部分标本的鳞片上有明显的幼轮标志;性成熟后,雌鱼的生长较雄鱼迅速;摄取的食物种类与湖中各种水生植物的季节性盛衰相适应,但有一定的选择性;亲鱼能在湖中成熟产卵,但鱼卵因受自然条件限制,不能发育成活。湖中鱼群的补充仍依靠数量不定的1龄幼鱼由长江干流逆水或顺水伺机窜入湖内。江湖之间闸门的启闭主要根据农田水利的需要,因此,长春鳊鱼群规律性的江湖交流仍然受到阻碍。