Environmental factors that define the spawning and nursery areas for Percophis brasiliensis (Teleostei: Percophididae) in a multispecific reproductive coastal zone, El Rincón (39°–41°S), Argentina

The spatial distribution of Percophis brasiliensis at different maturity stages and its relationship to environmental factors was evaluated in the El Rincon area (39°–41°S) between 1994 and 2008 during eight cruises carried out in spring. For this, a canonical correspondence analysis was used. Results indicate that bottom temperature and bottom salinity horizontal gradient (BSHG) were the most important variables affecting the spatial distribution of P. brasiliensis maturity stages. Juveniles were mainly located in shallow waters with low salinity, high temperatures and vertical stratification. Conversely, gravid and running individuals were found in high BSHG and low temperatures. This link suggests that adults spawn in a well-defined area of hydrographic conditions that would tend to retain pelagic eggs and larvae, thus minimizing dispersal, and ensuring their transport from the spawning to nursery areas. On the coastal shelf of El Rincon, the water mass circulation shows an anti-cyclonic gyre whose recirculation cell during spring and summer is more constrained to inshore areas than during winter. Maximum reproductive activity of P. brasiliensis coincides with the highest retention period; therefore, dispersal of early-life stages (eggs) depends on the circulation pattern and transport pathway which would contribute importantly to its recruitment variability.     

Using drift nets to capture early life stages and monitor spawning of the Yangtze River Chinese sturgeon (Acipenser sinensis)

A sampling system for capturing sturgeon eggs using a D-shaped bottom anchored drift net was used to capture early life stages (ELS) of Chinese sturgeon, Acipenser sinensis , and monitor annual spawning success at Yichang on the Yangtze River, 1996–2004, before and just after the Three Gorges Dam began operation. Captured were 96 875 ELS (early life stages: eggs, yolk-sac larvae = eleuthero embryos, and larvae); most were eggs and only 2477 were yolk-sac larvae. Most ELS were captured in the main river channel and inside the bend at the Yichang spawning reach. Yolk-sac larvae were captured for a maximum of 3 days after hatching began, indicating quick dispersal downstream. The back-calculated day of egg fertilization over the eight years indicated a maximum spawning window of 23 days (20 October–10 November). Spawning in all years was restricted temporally, occurred mostly at night and during one or two spawning periods, each lasting several days. The brief temporal spawning window may reduce egg predation by opportunistic predators by flooding the river bottom with millions of eggs. During 1996–2002, the percentage of fertilized eggs in an annual 20-egg sample was between 63.5 to 94.1%; however, in 2003 the percentage fertilized was only 23.8%. This sudden decline may be related to the altered environmental conditions at Yichang caused by operation of the Three Gorges Dam. Further studies are needed to monitor spawning and changes in egg fertilization in this threatened population.     

Distribution and abundance of fish eggs and larvae in three tributaries of the Upper Uruguay River (Brazil)

The present study aimed to investigate the distribution and abundance of fish eggs and larvae in three important tributaries (Chapecó, Peixe, and Ligeiro rivers) of the Upper Uruguay River. The spatial and temporal distribution of fish eggs and larvae were studied as well as the correlation between environmental parameters and the abundance of ichthyoplankton species. The study was conducted between October 2005 and September 2006. Ichthyoplankton samples were collected at night with cylindroconical 0.5-mm mesh plankton nets every 5 days. Of the 591 samples collected, 170 contained ichthyoplankton organisms, resulting in the capture of 12,847 fish eggs and 962 fish larvae. Twenty-seven fish species were observed, of which 69% were Characiforms and 27% were Siluriforms. Among the fish species captured, the representatives were predominantly young forms of small and medium size fishes, with rheophilic species occurring infrequently. Eggs occurred exclusively between October and January, while the highest larvae occurrence was observed between November and December. Fish larvae assemblage structure was shown to be related to some environmental variables. There was a tendency of higher values of water temperature and velocity at the lower sampling sites than at the upper ones, as well an increase number of eggs and larvae. The study tributaries serve as reproduction sites and nursery areas for several fish species of the Upper Uruguay River; thus, the maintenance of their integrity is important for the preservation of diversity and enhancement of fisheries in the region.     

Post‐hatch dispersal of lake sturgeon (Acipenser fulvescens,Rafinesque, 1817) yolk‐sac larvae in relation to substrate in an artificial stream

Knowledge of the effects of environment and genotype on behavior during early ontogenetic stages of many fish species including lake sturgeon (Acipenser fulvescens) is generally lacking. Understanding these effects is particularly important at a time when human activities are fundamentally altering habitats and seasonal and diel physical and biotic stream features. Artificial stream channels were used in a controlled experiment to quantify lake sturgeon yolk‐sac larvae dispersal distance and stream substrate preference from different females (N = 2) whose eggs were incubated at different temperatures (10 and 18°C) that simulated stream conditions during early and late spawning and incubation periods in the Black River, Michigan. Data revealed that yolk‐sac larvae exhibited considerable variability in dispersal distance as a function of family (genotype), temperature experienced during previous (embryonic) ontogenetic stages, and environmental ‘grain’. Yolk‐sac larvae dispersal distance varied as a function of the juxtaposition of substrate to location of egg hatch. Lake sturgeon yolk‐sac larvae dispersed from mesh screens attached to bricks and settled exclusively in gravel substrate. Dispersal distance also varied as a function of family and egg incubation temperatures, reflecting differences in offspring body size and levels of endogenous yolk reserves (yolk sac area) at hatch. Expression of plasticity in dispersal behavior may be particularly important to individual survival and population levels of recruitment contingent upon the location, size, and degree of fragmentation of suitable (gravel) habitats between adult spawning and yolk‐sac larvae rearing areas.     

Distribution and abundance of European hake Merluccius merluccius (L.), eggs and larvae in the North East Atlantic waters in 1995 and 1998 in relation to hydrographic conditions

Plankton samples from surveys in 1995 and 1998 were analysedin order to study the spatial distribution of hake (Merlucciusmerluccius) eggs and larvae. The cruises covered an extensivearea from the south of the Bay of Biscay to the north-west ofIreland. This spatial distribution has been interpreted in relationto the direction and intensity of the dominant winds. An importantdecrease of eggs (69%) and larvae (27%) was observed from 1995to 1998. Hake showed continuous spawning from February to Julyin the area. The centroids of hake egg distribution indicateda northward displacement of the peak of spawning as the seasonprogresses. Spawning of hake was located close to the 200 mdepth isobath in the southern area (Bay of Biscay) and it spreadover the shelf in the area of the Celtic Sea. Eggs were mostabundant at 20 m depth temperatures between 12 and 12.5°C.The centroids of hake larvae distribution also showed a northwarddisplacement although not as strong as that of hake eggs. Thespatial distribution of hake larvae by size ranges showed importantdifferences between years: in 1995 it suggested inshore transportof larvae, from the spawning areas (close to the 200 m depthisobath) to nursery areas (closer to the coast) while in 1998it suggested offshore transport. This transport does not correspondwith the general wind regimes during those years. Thereforeit is concluded that the transport of the hake larvae to nurseryareas must be controlled by different hydrographic mechanismssuch as geostrophic currents in the Bay of Biscay and tidalcurrents in the northern areas.     

Species-specific genetic markers for identification of early life-history stages of Cape hakes, Merluccius capensis and Merluccius paradoxus in the southern Benguela Current

The correct identification of fish egg and larval stages is crucial for inferring spawning areas and subsequent dispersal routes for marine fishes. The authors use species-specific mtDNA polymerase chain reaction to estimate proportions of Merluccius capensis and Merluccius paradoxus eggs and larvae and to elucidate early life stage distribution patterns in the southern Benguela system.     

Changes in spatial distribution pattern during the larval stage of the fall webworm,Hyphantria cunea drury (Lepidoptera: Arctiidae)

Summary The changes in spatial distribution pattern during larval stage of the fall webworm,Hyphantria cunea were quantitatively investigated in the field experimental populations. The female adult deposits eggs as a cluster and the hatchlings make a compact colonial-web. In this period, the all-or-none type mortality which is characteristic in gregarious insect species was occasionary recognized before spinning a compact colonial-web. Once making a compact colonial-web, the larvae feed the leaves in the colonial-web up to about 5th instar. In this period, the movement of larvae occurred due to the local food shortage in a colonial-web and the expansion of colonial-web. As the larvae developed, the colonial-web was separated into several small groups. These larvae began to disperse about 5th instar. In this period, the local food shortage seems to be an important trigger for the larval dispersal. The mean concentration of larvae on leaves abruptly decreased, and finally the larvae became solitary at the 6th or 7th instars. The dispersal process in later larval stage is not necessarily due to the complete food shortage. The dispersal prior to the occurrence of food shortage may be a safety mechanism to protect the larvae from the food shortage.     

Diel patterns of larval drift of honmoroko Gnathopogon caerulescens in an inlet of Ibanaiko Lagoon,Lake Biwa,Japan

Diel drift patterns of larvae of the endangered cyprinid Gnathopogon caerelescens in an inlet of the Ibanaiko Lagoon, connected to Lake Biwa in Japan, were assessed in April 2012. Peak occurrence of yolk‐sac larvae was within a few hours after dark. Drift of newly hatched larvae is considered to be an important biological mechanism that ensures larval dispersal and recruitment from the inlets (spawning grounds) to the lagoon which functions as a nursery ground.     

Anchovy egg and larval distribution in relation to biological and physical oceanography in the Strait of Sicily

The European Anchovy (Engraulis encrasicolus, Linnaeus, 1758) represents one of the most important fishery resources in some areas of the Mediterranean. This short-lived, small pelagic fish is characterized by large interannual fluctuations, probably as a result of environmental variability. As part of the European Project Med 98-070, the main aim of which was the study of the anchovy population in the Strait of Sicily, icthyoplankton surveys were carried out between 1999 and 2001, during the peak spawning season for anchovy. Present work reports the relationship between meso-zooplankton biomass and the abundance of anchovy eggs and larvae in the Strait of Sicily. Data on anchovy egg abundance showed that the main spawning area was located in the north-western region of the study area. The branch of the Atlantic Ionian Stream, running parallel to the southern Sicilian coast, acts as a transport mechanism for anchovy eggs and larvae towards the southernmost end of the island, off Cape Passero. Observed distributions were largely consistent with local hydrographic features, which allow larvae to be retained in areas providing the necessary feeding conditions for recruitment success.     

A bedform morphology hypothesis for spawning areas of Chinese sturgeon

Results from previous research suggested that geomorphic characteristics may be important controlling factors among other microhabitat variables for spawning fish. We investigated the bedform morphology of seven spawning areas (five historic and two present spawning areas) of Chinese sturgeon (Acipenser sinensis) by analysis of relief maps of the riverbed and by field surveys. We conclude that the topographic characteristics of the spawning areas include rocky or gravelly substrate river bend, large variations in water depth and river width and a slope with moderate length and slope. The turning structure and the adverse slope may be the most important topographic characteristics for the spawning areas. Combined with the reproductive occurrence of the fish in these spawning areas, we tentatively propose a bedform morphology hypothesis for the spawning areas. We consider that a spawning area of A. sinensis should consist of three functional areas: Mating area (M), Dispersal area (D) and Incubation area (I). M, D and I are distributed along the water current and their bedform characteristics are clearly different. M is the place for mature fish to mate and spawn. It is usually below a riffle with rolling terrain. D is the place for fertilizing and dispersing fertilized eggs. It is usually in a river bend with sharp variations in terrain, such as deep pools or steep slopes. I is the place for dispersal of fertilized eggs. It is usually in long point bars or broad shallow areas with rocky substrate. This hypothesis could serve as a guideline for improving the present spawning areas or constructing new spawning areas, so as to rehabilitate the wild stock of the sturgeon.     

Vertical distribution of eggs and larvae of the Baltic Sprat <Emphasis Type="Italic">Sprattus sprattus balticus</Emphasis> (Clupeidae) in relation to seasonal and diurnal variation

Vertical distribution of eggs and larvae of the Baltic sprat Sprattus sprattus balticus was studied. Diurnal variation was revealed in the distribution of eggs of the first stage of development and larvae with a length of more than 5 mm, which is related to dynamics of spawning and vertical migrations of sprat larvae. Seasonal variation in the distribution of eggs manifested itself in: (1) widening of the range of occurrence from the zone of halocline at the beginning of spawning (winter) to the entire water column in spring-summer and (2) emergence in the surface layer in July of all stages of egg development unlike the presence from May to June mainly of the first stage of development. It is suggested that the ability of early ontogenetic stages of sprat to maintain in the surface layer depended on the extent of development of vertical gradients of density in the thermocline.     

Reproductive biology of four large riverine fishes (Cyprinidae) in a man-made lake,Orange River,South Africa

The reproductive biology ofBarbus holubi, B. kimberleyensis, Labeo capensis andL. umbratus was examined in a large reservoir on the Orange River, South Africa. The findings are integrated into the existing knowledge on largeBarbus andLabeo species, which coexist in most river systems in Africa and Asia.LargeBarbus spawn on gravel beds within the river channel during floods in spring or summer. In continuously flowing regulated rivers, time of spawning is governed by water temperatures. They have moderate fecundity; large eggs, incubation time of several days and the larvae are initially immobile with large yolk sacs. In the impoundment, they spawn in the inflowing regulated river withB. kimberleyensis spawning four to six weeks later than the more cold-tolerantB. holubi, the dominant largeBarbus. Survival is generally good and the juveniles disperse throughout the lake, but unseasonal release of cold water from an upstream impoundment may cause poor reproductive success.In contrast,Labeo species generally spawn on newly flooded ground, usually leaving the main river channel. Spawning may or may not be preceded by a longitudinal migration. Labeos are relatively fecund with small (30%Barbus size) eggs which hatch quickly and the larvae swim in bursts up into the water column before sinking down again.L. capensis does not require a longitudinal spawning migration and breeds throughout the lake, depending on local conditions. Large temporal variation in gonadal development within the population can result in more than one spawning. Dispersal within the lake is poor.L. umbratus uses larger inflowing tributaries for spawning thanL. capensis and its juveniles have a much greater power of dispersal. Early dependence on external feeding and undependable occurrence of conditions for spawning and juvenile feeding makes for variable reproductive success.     

Implications of early life stages in the natural history of the Gulf of Mexico sturgeon,Acipenser oxyrinchus de sotoi

Synopsis Gulf of Mexico sturgeon were collected during their natural spring spawning migrations from the Gulf of Mexico into the Suwannee River in Florida. Peak numbers were observed during March and April. During the summer periods the fish remained in the river over very localized bottom areas. In late fall, the fish migrated from the river into the Gulf of Mexico. Laboratory experiments revealed that maximum survival of eggs, embryos and larvae of Gulf of Mexico sturgeon occurred between 15 and 20° C. Although Gulf of Mexico sturgeon appear to have a high tolerance to warm water temperatures, their embryos and larvae exhibit high mortalities at temperatures of 25° C. Based on observations of Gulf of Mexico sturgeon migratory patterns and laboratory experiments we suggest that the timing and unusual migratory behavior of Gulf of Mexico sturgeon are associated with temporal water temperature changes in the river and the Gulf of Mexico. The requirements of a thermal refuge are discussed.     

Description of Rhynchoteuthion larvae of Illex argentinus from the summer spawning subpopulation

The Rhynchoteuthion larvae of Illex argentinus resulting fromsummer spawning in North Patagonic shelf waters, its distributionand abundance, are described in this paper. The material wascollected in the Argentine Sea (35–55°S) by meansof plankton nets. The research cruises were made by the R/VShinkai Maru and the R/V Walther Herwig during the period April1978 to April 1979. The most important spawning ground of thesummer spawning subpopulation is found in continental-shelfwaters (between 43 and 46°S) during the period December-February.This area was established on the basis of both ripe (December)and spent females (February). The larvae which were caught duringthe same period, especially in March, confirmed the spawningarea of this demographic unit. The larvae showed the lengthof the mantle (ML) to be from 1.2 to 6.5 mm. Tentacles weresplitting in specimens from 5.0 to 6.5 mm ML (transition stage).When 7.0 mm ML or more, all specimens were juveniles and hadtheir tentacles completely separated. Larvae were characterizedas type C, following the proposal of Sato (1973) and Sato andSawada (1974) in the Bulletin of the Shizuoka Prefectural FisheriesExperimental Station.     

Replenishment of fish populations in the enclosed lagoon of Taiaro Atoll: (Tuamotu Archipelago, French Polynesia) evidence from eggs and larvae

 Taiaro Atoll Lagoon is normally isolated from the ocean, but at least 125 marine fish species of 31 families are present there. We sampled fish larvae in Taiaro Lagoon and the nearby ocean in February 1994 with plankton net, neuston net and light trap to investigate which taxa were completing their life cycles in the lagoon. Concentrations of fish eggs and larvae were very high in the lagoon indicating intense spawning, but larvae of only 18 taxa of 10 families were present. Only six, a callionymid, gobiids, a hemiramphid, a microdesmid, and two pomacentrids, were present across a full range of pelagic sizes, and were clearly completing their pelagic stage in the lagoon. Four other taxa, an apogonid, two labrids and a scarid, were common, but the largest individuals were small (<5 mm) postflexion larvae. These may have been completing their pelagic stage in the lagoon. The remaining lagoonal larvae (eight taxa) were rare and at the preflexion stage, so we could only conclude that they hatched from eggs spawned in the lagoon. Nineteen taxa of 15 families found as adults in the lagoon were present outside the lagoon as larvae, but not inside, suggesting that they may not normally complete their life cycles in the lagoon. Horizontal distributions of larvae in the lagoon are apparently due to the interaction of larval vertical distribution behaviour with a wind-driven countercurrent system. Accepted: 16 October 1996     

珠江东塔产卵场鳙繁殖的生态水文需求

鳙(Aristichthys nobilis(Richardson)),我国著名的四大家鱼之一,是一种重要的大型淡水经济鱼类。然而近年来由于各种原因,我国鳙种群数量急剧下降。依据2006—2013年珠江中下游长时间序列仔鱼数据和日平均流量数据,分析了研究水域鳙的繁殖生态,包括仔鱼出现的时间分布特征和早期资源周年变化规律,同时采用交互小波光谱分析方法 (cross wavelet analysis),分析了径流量与鳙仔鱼多度的关系。发现珠江水系鳙早期资源发生主要在5至8月,2006—2011年早期补充资源量逐渐减少,2012—2013年间呈明显著增加;鳙早期资源年度出现的时间呈缩减趋势,其中最大繁殖量出现的时间逐年提前。交互小波光谱分析结果表明:径流量的改变与鳙仔鱼的多度显著正相关,当径流量大于5×103m3/s,且持续2d以上,是珠江水系鳙大量繁殖的基础,将对受梯级水坝控制的鳙产卵场的繁殖生态水文保障具有指导意义。     

Field mortality estimates of anchovy larvae, Engraulis encrasicolus, in the western Mediterranean

Eggs and larvae of anchovy were obtained from plankton collections made along the Catalan coast (north-western Mediterranean) from 1983 to 1985 in order to determine spawning seasons and areas and other aspects of its life history. Previous studies have shown the existence of two main spawning areas, to the north and south of the Catalan coast, respectively. The northern one is characterized by a shorter spawning period related with the thermal cycle.
Mortality rates of larvae aged 4.9-15 days were calculated from the peak spawning month (June) of the three years, separately by spawning areas. Data on abundance by length classes were adjusted for escape and net avoidance and for duration of growth through a size class as derived from otolith readings. Mortality rates ranged from 0.17 to 0.58. Mortality was higher in 1983 than in 1984 and 1985, coinciding with a high production of anchovy eggs in that year. Mortality at the northern spawning area was lower than at the southern one.     

Spatial and temporal occurrence of Rhabdostyla cf. chironomi Kahl, 1933 (Ciliophora, Peritrichia) as an epibiont on chironomid larvae in a lotic system in the neotropics

In order to show how environmental factors could influence the spatial and temporal distribution of epibiosis, we investigated the occurrence of the ciliate Rhabdostyla cf. chironomi (Ciliophora, Peritrichia) attached to Chironomidae larvae in an urban stream in southeast Brazil. Samples were collected monthly for 1-year period at five sampling stations along the stream. Among the 24 genera analyzed, the genus Chironomus was the most abundant, with 16.84% carrying R. cf. chironomi. This epibiotic relationship was only recorded in sample stations located in a heavily populated urban area of the stream. Statistical analyses demonstrated significant correlations between infestation prevalence and environmental parameters such as rainfall, bacterial density, and host abundance. The occurrence of epibionts on the larvae was spatially and temporally heterogeneous. The results are discussed in terms of possible factors related to the heterogeneous spatial and temporal occurrence. Greater understanding of the ecological factors governing the occurrence of the epibiont–host relationship is essential to establish future use of this relationship as water quality indicator in lotic systems.     

Reproduction characteristics of a stunted population of rudd, <Emphasis Type="Italic">Scardinius erythrophthalmus</Emphasis> (Linnaeus, 1758) living in the Anzali Lagoon (the southwest Caspian Sea,Iran)

A total of 486 specimens of Scardinius erythrophthalmus caught in the Anzali lagoon, a large lagoon located in the southwest Caspian Sea (Iran), between March and June 2007 were examined. Age determination showed that the maximum ages observed were 4+ in males and 5+ in females. Isometric growth was identified from length-weight relationship in males, females and pooled data. There was no significant difference from parity in the overall sex ratio of 252 males to 234 females. The fish spawn from mid April to late May, with peak spawning in mid May with the highest average GSI value of 7.12 and 13.52 for males and females respectively. The absolute fecundity ranged between 1482–59620 eggs with the mean of 9287.87 eggs while relative fecundity ranged from 127.8 to 1737.6 eggs/g with the average of 709 eggs/g of body weight. Egg diameter ranged from 0.43 to 1.23 mm with a mean of 0.73 mm. The characteristics of rudd in the stunted population from the Anzali lagoon differ markedly from those of other localities of its range.     

Embryonic development and larval behavior of the kissing loach (<Emphasis Type="Italic">Parabotia curta</Emphasis>): adaptations to an ephemeral,hypoxic environment

Many teleost fishes in lowland fresh waters spawn in ephemeral flooded areas, the bottoms of which are prone to hypoxia. Little is known about how embryos and larvae deal with these potentially hostile environments. This study examines the functional and behavioral ontogeny of one such species, the kissing loach (Parabotia curta). Kissing loach eggs are demersal and adhesive. Hatching occurs at 24.8 ± 0.1 h post-fertilization at 25°C, much earlier than most fish species. The newly hatched larvae are precocious with no functional mouth, fins or eye pigmentation. Swimbladder inflation normally occurs at about 4 days posthatch, even before which the hatched larvae moved immediately toward the water surface to hang from water moss. Experiments with larvae 20 h after hatching showed that they spent significantly less time on the bottom in hypoxic water (2 mg/l) than in normoxic water, and suggest that hypoxia is a major directive factor in eliciting surfacing behavior. For the kissing loach, we have previously reported short-term spawning after the formation of flood areas as well as wide scattering of the spawned eggs in the temporal flooded areas. These traits with the present results of hatching at an early stage and the immediate upward movement of larvae are considered to be effective strategies for using ephemeral, hypoxic flooded areas for reproduction.