The effects of light intensity and algae-induced turbidity on feeding behaviour of larval striped trumpeter

Striped trumpeter larvae reared in algal cell‐induced turbid water (greenwater) fed equally well in clearwater in a light intensity range of 1–10 μmol s^‐1 m^‐2, when evaluated in terms of both the proportion of larvae feeding and larval feeding intensity. An ontogenetic improvement in photopic visual sensitivity of larvae was indicated by improved feeding at 0·1 μmol s^‐1 m^‐2, from 26±5% of larvae feeding and 0·027±0·005 rotifers consumed per feeding larva min^‐1 on day 8, to 96±2% and 0·221±0·007 rotifers consumed larva^‐1 min^‐1 on day 23 post‐hatching. Algal cell‐induced turbidity was shown to reduce incident irradiance with depth, indicated by increasing coefficients of attenuation (1·4–33·1) with increasing cell densities (0–2×10⁶ cells ml^‐1), though light intensities in the feeding experiment test chambers, at the algal cell densities tested, were within the optimal range for feeding (1–10 μmol s^‐1 m^‐2). Algae‐induced turbidity had different effects on larval feeding response dependent upon the previous visual environment of the larvae. Young larvae (day 9 post‐hatching) reared in clearwater showed decreased feeding capabilities with increasing turbidity, from 98±1% feeding and 0·153±0·022 rotifers consumed larva^‐1 min^‐1 in clearwater to 61±10% feeding and 0·042±0·004 rotifers consumed larva^‐1 min^‐1 at 56 NTU, while older clearwater reared larvae fed well at all turbidities tested. Likewise, greenwater reared larvae had increased feeding capabilities in the highest algal cell densities tested (32 and 66 NTU) compared with those in low algal cell density (6 NTU), and clearwater (0·7 NTU) to which they were naïve.     

Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis

The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l⁻¹) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 μmol s⁻¹ m⁻² at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s⁻¹ m⁻²), with fish capturing up to 5 prey larva⁻¹ h⁻¹. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s⁻¹ m⁻²) exceeding 100 prey larva⁻¹ h⁻¹. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s⁻¹ m⁻², remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva⁻¹ h⁻¹) that was independent of larval age.     

Ontogeny of critical and prolonged swimming performance for the larvae of six Australian freshwater fish species

Critical (<30 min) and prolonged (>60 min) swimming speeds in laboratory chambers were determined for larvae of six species of Australian freshwater fishes: trout cod Maccullochella macquariensis, Murray cod Maccullochella peelii, golden perch Macquaria ambigua, silver perch Bidyanus bidyanus, carp gudgeon Hypseleotris spp. and Murray River rainbowfish Melanotaenia fluviatilis. Developmental stage (preflexion, flexion, postflexion and metalarva) better explained swimming ability than did length, size or age (days after hatch). Critical speed increased with larval development, and metalarvae were the fastest swimmers for all species. Maccullochella macquariensis larvae had the highest critical [maximum absolute 46·4 cm s^?1 and 44·6 relative body lengths (L_B) s^?1] and prolonged (maximum 15·4 cm s^?1, 15·6 L_B s^?1) swimming speeds and B. bidyanus larvae the lowest critical (minimum 0·1 cm s^?1, 0·3 L_B s^?1) and prolonged swimming speeds (minimum 1·1 cm s^?1, 1·0 L_B s^?1). Prolonged swimming trials determined that the larvae of some species could not swim for 60 min at any speed, whereas the larvae of the best swimming species, M. macquariensis, could swim for 60 min at 44% of the critical speed. The swimming performance of species with precocial life‐history strategies, with well‐developed larvae at hatch, was comparatively better and potentially had greater ability to influence their dispersal by actively swimming than species with altricial life‐history strategies, with poorly developed larvae at hatch.     

Effect of water velocity and temperature on energy use,behaviour and mortality of pallid sturgeon Scaphirhynchus albus larvae

Natural reproduction of pallid sturgeon Scaphirhynchus albus has been limited for decades and a recruitment bottleneck is hypothesized to occur during the larval stage of development. In this study, we evaluated the effects of water velocity and temperature on the swimming activity, energy use, settling behaviour and mortality of endogenously feeding larvae. The swimming activity of drifting sturgeon larvae (i.e., fish exhibiting negative rheotaxis) increased at low water velocity. In subsequent experiments, we observed greater energy depletion and resultant mortality of larvae in no-flow environments (0 cm s⁻¹) compared to tanks with water velocity ranging from 3.5 to 8.3 cm s⁻¹. The growth rate of drifting larvae was positively related to water temperature (18.7–23.3°C), but reduced growth rate at low water temperature (18.7°C) resulted in protracted development that extended average drift duration by ~4 days compared to larvae reared at 23.3°C. This study provides evidence that cooler summer water temperatures, characteristic of present-day conditions in the upper Missouri River, can reduce larval development and extend both the drift duration and distance requirements of S. albus. Moreover, if dispersed into low velocity environments, such as in reservoir headwaters, larvae may experience increased mortality owing to a mismatch between early life stage drift requirements and habitat conditions in the river. Manipulation of water releases to increase seasonal water temperature below dams may aid survival of S. albus larvae by shortening the time and distance spent drifting.     

Evaluating the effects of controlled flows on historical spawning site access,reproduction and recruitment of lake sturgeon Acipenser fulvescens

Lake sturgeon Acipenser fulvescens spawn at the base of Kakabeka Falls, a 39 m waterfall on the Kaministiquia River, a tributary to Lake Superior. Access to this historical spawning site can be restricted or delayed due to hydroelectric flow fluctuations that coincide with the A. fulvescens spawning season. The objectives of this study were to determine (a) the necessary flow conditions that facilitate spawning site access; (b) quantity and duration of flow required for successful spawning and dispersal of larvae; and (c) evaluate recruitment of juvenile A. fulvescens in relation to flow. A. fulvescens spawning migrations were tracked using a stationary telemetry receiver that logged the movements of 166 A. fulvescens fitted with radio-transmitters. Unrestricted access to the spawning site was facilitated when spawning flow was controlled at 23 m³ s⁻¹ in 2004 and 17 m³ s⁻¹ in 2006. Fluctuating (0.5–8.5 m³ s⁻¹) and delayed spawning flows resulted in restricted and delayed access to the spawning site. Flow duration for successful egg incubation, hatch and larval dispersal was determined by sampling larvae using drift nets and quantified using cumulative temperature units (CTU). Over 10 years, 10,083 larvae were captured between 31 May and 20 July with 97% of the drift occurring prior to 30 June. From the date of first spawning to the end of larval dispersal took an average of 38.6 days, and the mean CTU value was 398.6. In general, a minimum flow of approximately 14.5 m³ s⁻¹ from the date of initial spawning to the accumulation of c. 400 CTU ensured successful hatch and larval dispersal. During the timeframe of this study, recruitment was variable. This study described the complex and variable reproductive life history of A. fulvescens and defined spawning flow requirements ecologically, which can be used to develop operational provisions at hydropower facilities to ensure successful reproduction.     

Effect of turbulence on feeding intensity and survival of Japanese flounder Paralichthys olivaceus pelagic larvae

Three‐day rearing experiments were conducted to study the effect of turbulence on the feeding intensity and survival of pelagic larvae of Japanese flounder Paralichthys olivaceus. Four levels of turbulence as control (10^?7·2 m² s^?3), low (10^?6·2 m² s^?3), mid (10^?5·6 m² s^?3) and high (10^?5·0 m² s^?3) were set by changing the flow rate of water pumped through pipes set on the bottom of the tanks. In B‐stage larvae, defined as having buds of elongated dorsal fin rays, the feeding intensity and growth were higher in the low and mid turbulence levels, while survival was highest in the control level. Most of the larvae surviving in the control level, however, were judged to be in a seriously starved condition leading to subsequent high mortality. Because the three‐day span of the rearing experiments was thought to be a little shorter than the periods before starvation‐induced, high mortality occurs. In contrast, for D‐stage larvae, their feeding and growth were optimal in the control and low levels. Feeding was more adversely affected in the high level for D‐stage larvae compared with B‐stage larvae. This is probably due to the compressed body shape and elongated dorsal fin rays of D‐stage larvae, which may be more strongly affected by turbulence and, as a consequence, the larval feeding behaviour such as pursuit and capture of prey organisms becomes less efficient than in lower turbulence. Considering the vertical distribution of B and D‐stage larvae in the oceanic water column, the optimum turbulence level range found in the present study corresponded to a wind speed of 7–10 m s^?1. Therefore, moderate weather conditions of this wind speed range are considered to potentially enhance survival of early larval stages of P. olivaceus.     

Timing of paddlefish spawning in the Upper Missouri River,Montana, USA in relation to river conditions

Spawning activity of paddlefish Polyodon spathula in the Missouri River, Montana in 2008–2009 was examined to delineate spawning sites and times in relation to discharge, water temperature and turbidity. One hundred thirty‐six eggs were collected at water temperatures ranging from 12.0 to 20.7°C (mean, 16.3°C; SD, 2.5). Only 12 of 89 (13%) congregations of radio‐tagged adults observed during the spawning period coincided with egg captures. Six larvae were collected at water temperatures ranging from 19.1 to 21.7°C (mean, 20.5°C; SD, 0.86). Peak discharge in 2008 (903 m³ s^?1 on 14 June) was approximately 30% greater in magnitude and occurred 11 days later than peak discharge in 2009 (612 m³ s^?1 on 3 June). Despite these differences in the hydrograph, no significant differences in egg CPUE were found between years (anova , F = 0.69, P = 0.56). Logistic regression identified no significant river condition variables associated with the presence or absence of eggs (P > 0.14 for all variables). However, in both years maximum egg CPUE was recorded within 3 days of the hydrograph peak and at similar water temperatures (17.5°C in 2008, 16.8°C in 2009). These results suggest an overall association of peaking discharge and seasonally warming water temperatures with egg deposition. Higher catches of eggs and larvae than observed in this study may be necessary to clarify short‐term (day‐to‐day) effects of environmental changes on spawning activity. Continued investigation of the relationship between short‐term changes in river conditions and paddlefish spawning activity is needed to understand the mechanics underlying the reproductive success of this species.     

Habitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes in the lowland rivers of Central Europe

The pattern of microhabitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes was examined in two rivers of central Poland: the Pilica River (the Vistula River basin) and the Grabia River (the Odra River basin). A comparison of abiotic factors of the rivers revealed differences in water speed and principal components: PC1 (determining gradient from decreasing medium sand to the increasing share of three fractions of gravel), PC2 (a gradient from the declining share of very coarse and coarse sand fractions to the growing content of fine sand) and PC3 (correlated with an increasing proportion of silt). The sites did not differ significantly in terms of water depth. Relative abundance and frequency of ammocoete occurrence in the Grabia River were higher than in the Pilica River. Only speed, PC1 and PC2 made a significant contribution to the prediction of larval occurrence. Eudontomyzon mariae larvae preferred substrata with a reduced amount of medium sand and increased content of gravel (PC1) as well as with a lower content of coarse sand and higher proportion of fine‐grained sand (PC2). The ammocoetes also preferred areas with a water speed of 0·2 m s^?1 but avoided speeds ≥0·6 m s^?1. The abundance of E. mariae was affected by water speed, as well as by all PCs. The mean ± s.e. optimal current speed was 0·265 ± 0·007 m s^?1, while abundance decreased with increasing amounts of gravel (PC1) and increased with increasing amounts of fine sand and silt in the bottom substratum (PC2 and PC3). Comparison of ammocoete microhabitat use in the Pilica and Grabia Rivers showed the lack of differences in distribution in the preferred values of current speed, PC1 and PC2.     

Life history of a lowland burrowing mayfly, Ephemera orientalis (Ephemeroptera: Ephemeridae), in a Korean stream

Life history aspects of Ephemera orientalis, a common lowland burrowing mayfly that resides in temperate East Asia, were studied in terms of voltinism, secondary production, and accumulated degree days for larval development. From March 1998 to June 1999, larvae were sampled monthly (weekly or biweekly during the emergence period) from a lower reach of the Gapyeong stream in Korea, a stream typical of temperate East Asia, using a Surber sampler (0.25 m², mesh 0.25 mm). As a result, the mean density of E. orientalis was 47.21 ± 13.58 indiv. m⁻² during the study period. Very small larvae less than 2 mm in body length were sampled on three separate occasions, and emergence was observed between late April and early October, except during late May. Based on the larval body length distribution and emergence time, two different developmental groups could be distinguished: the slow developmental group (S-group) and the fast developmental group (F-group). The F-group completed its life cycle within 4 months, whereas the S-group had a one-year life cycle. The S-group could be divided into two subgroups, dubbed the S1 and S2-groups, based on larval development. The developmental groups alternate their life cycles in the order: S1→F→S2→S1. Estimated annual production of the larvae was 68.81 mg DW m⁻² y⁻¹; mean biomass was 8.43 mg DW m⁻²; the annual production to mean biomass ratio was 8.16. The annual mean water temperature of the study year was 14.76 ± 6.63°C. The total accumulated degree days for larval development was 1396°C for the F-group, 2,055°C for the S1-group, and 1,975°C for the S2-group. Two different adult body size groups were distinguished (P < 0.001 by t-test): larger adults, which belonged to the S-group, were present throughout the emergence period, whereas smaller adults, which belonged to the F-group, were mainly present later in the emergence period (August–October). The difference in the accumulated degree days between the developmental groups may explain the size differences of adults.     

Ontogeny of body density and the swimbladder in yellowtail kingfish Seriola lalandi larvae

The ontogeny of larval body density and the morphological and histological events during swimbladder development were investigated in two cohorts of yellowtail kingfish Seriola lalandi larvae to understand the relationship between larval morphology and body density. Larvae <3 days post hatch (dph) were positively buoyant with a mean ± s.d . body density of 1·023 ± 0·001 g cm^?3. Histological evidence demonstrated that S. lalandi larvae are initially transient physostomes with the primordial swimbladder derived from the evagination of the gut ventral to the notochord and seen at 2 dph. A pneumatic duct connected the swimbladder to the oesophagus, but degenerated after 5 dph. Initial swimbladder (SB) inflation occurred on 3 dph, and the inflation window was 3–5 dph when the pneumatic duct was still connected to the gut. The swimbladder volume increased with larval age and the epithelial lining on the swimbladder became flattened squamous cells after initial inflation. Seriola lalandi developed into a physoclist with the formation of the rete mirabile and the gas‐secreting gland comprised low‐columnar epithelial cells. Larvae with successfully inflated swimbladders remained positively buoyant, whereas larvae without SB inflation became negatively buoyant and their body density gradually reached 1·030 ± 0·001 g cm^?3 by 10 dph. Diel density changes were observed after 5 dph, owing to day time deflation and night‐time inflation of the swimbladder. These results show that SB inflation has a direct effect on body density in larval S. lalandi and environmental factors should be further investigated to enhance the rate of SB inflation to prevent the sinking death syndrome in the early life stage of the fish larvae.     

Reproductive strategy and recruitment dynamics of amphidromous goby Sicyopterus japonicus as revealed by otolith microstructure

The daily ages of 312 of 879 newly recruited postlarvae of Sicyopterus japonicus, collected from the Shuang‐Chi Estuary in north‐eastern Taiwan during February 1996 to April 1997, were determined from daily growth increments in their otoliths. Pelagic larval duration, growth rate of the marine larval stage and hatching dates were estimated, and recruitment timing was linked to environmental factors. The mean ±s .d . total length (L_T) and daily ages of S. japonicus at recruitment to the estuary were estimated to be 33·95 ± 1·31 mm (range 30·7 to 38·1, n = 317) and 163·72 ± 12·79 days (range 130 to 198, n = 312), respectively. The recruitment of S. japonicus larvae is size dependent not age dependent because L_T of the larvae is independent of age at recruitment. Periodic analysis indicated that L_T and growth rate of the larvae were inversely correlated with the age at recruitment, which means that the fast‐growing individuals recruited earlier. The growth rate of S. japonicus in the marine larval stage was synchronous with marine productivity in this subtropical area, i.e. the spring cohort recruited in the autumn had a higher growth rate than the autumn cohort recruited the following spring. The main spawning season of S. japonicus as backcalculated from otolith daily increments was in autumn, a relatively low productivity period compared with spring. During this season, there were fewer competitors and predators than in the more productive spring. The recruitment of 95% of postlarva coincided with low salinity (14) and low water temperature (23° C) in the river mouth that provided a buffer area for the adaptation of the larvae for upstream migration. This unique reproduction strategy and prolonged larval duration facilitated the widespread distribution of the fish along the coasts of East Asia.     

Occurrence of Gobiidae larvae in a tropical Brazilian estuary,with particular emphasis on the use of size classes to categorize species guilds

The structure and seasonal dynamics of larvae of the Gobiidae family in the Mucuri Estuary (Bahia, Brazil) were studied for nine consecutive years. Sampling was conducted at three stations in the lower estuary channel, between 2002 and 2010, in relation to season, day and night and tidal variations. A total of 5802 Gobiidae larvae, representing 15 taxa (12 species and three morphotypes), were collected in the Mucuri Estuary during this time. The highest mean ± s.d. density of fish larvae, 54·7 ± 79·8 larvae 100 m^?3, was recorded during the flood tide and night sampling. Ctenogobius boleosoma was the most abundant species (68%), being dominant in the rainy and dry seasons and had a long reproductive period. This species was classed as a marine estuarine‐opportunist because it was observed at high frequencies and active larvae entering the estuary between 6·1 and 12·0 mm standard length (L_S). Gobionellus oceanicus, second in abundance (12%), occurred only in later larval stages but did not use the estuary as a preferred location for spawning, being classed a marine estuarine dependent. Microgobius carri (11%) was represented in all L_S classes and was resident in the estuary for spawning, remaining there throughout their life cycle. The other species were considered rare due to their low densities and could not be classified in any guild.     

Reservoir manipulations and benthic macroinvertebrates in a Prairie River

Samples were taken on the Tongue River, Montana, USA, during 1974 and 1975 to determine the distributions and abundances of the benthic fauna after various reservoir manipulations. The upper cold water section, influenced by hypolimnial discharge from the Tongue River Reservoir, was impoverished in insect fauna and dominated by the molluscs Physa and Sphaerium. The lower warm water sections of the river contained two communities determined primarily by turbidity and periphyton cover. The upper warm water area was dominated by Strophopteryx and hydropsychid caddis larvae. The lower river was dominated by Cheumatopsyche. The summer fauna, in the warm water area, was dominated by short-lived mayfly species. During the summer, 1975, the cold water section was invaded by many insects due to warming of the area when no hypolimnion was formed in the reservoir. Invasion was apparently due to increased thermal fluctuations which caused diapause eggs to hatch and influenced the upstream migration of older nymphs and larvae.Results of drift and distributional samples after closure of the Tongue River Reservoir Dam for repairs showed that massive drift of all invertebrates began at a discharge of 130 c.f.s. (3.68 m³/sec), a drop from 190 c.f.s. (3.38 m³/sec) over a period of three days. Community composition was radically altered by reduced discharge.     

The relation between invertebrate drift and two primary controls,discharge and benthic densities,in a large regulated river

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Annual variability in upstream migration of glass eels in a southern USA coastal watershed

We investigated the environmental factors that affected temporal variability of eel recruitment and upstream migration in a freshwater coastal river along the southeastern US. Glass eels Anguilla rostrata were collected through ichthyoplankton sampling in the lower Roanoke River, North Carolina. Monthly samples were taken from fixed stations from May 2001 through June 2003. There was no evidence of consistent seasonal migration patterns for glass eels in Roanoke River. From May through December in 2001, glass eels were captured only during August. In 2002, glass eels arrived in February and remained in ichthyoplankton samples through October, with the exception of samples from September. Peak catch occurred in March at 4.02 ± 1.2 and declined through June to 0.18 ± 0.07 (#/1,000 m³). By August, the mean density increased to 0.96 ± 0.82 and to 3.59 ± 2.77 by October. In 2003 from January through June, glass eels were captured only during February and March. Glass eels were routinely collected when river discharge rates were <150 m³ s⁻¹. River discharge rates >650 m⁻³ s⁻¹ resulted in no glass eels in our samples. Upstream migration during 2002 was not correlated with water temperature or related to lunar phase. Glass eel freshwater upstream migration was initiated when water temperatures exceeded a threshold range of 10°C to 15°C; however, glass eels continued to migrate when water temperatures approached 30°C. The overall negative effect of river discharge suggests that changes in the water release schedules of upstream hydroelectric facilities during glass eel migration could strongly influence their recruitment success.     

Habitat and substrate influences on population and production dynamics of a stream caddisfly, Ceraclea ancylus (Leptoceridae)

SUMMARY. Population and production dynamics of Ceraclea ancylus (Vorhies), a leptocerid caddisfly with a univoltine life cycle, five larval instars, and a single cohort population, were examined in Brashears Creek, Kentucky. A systematic sampling approach that included analysis in riffle, pool, and waterwillow bed habitats was used and fourteen sampling transects were taken across Brashears Creek between May 1971 and July 1972. For each of the 70 m² samples taken along a transect, the depth, habitat, and substrate type were recorded. The number of C. ancylus cases and numbers and dry weights of each larval instar were determined. The majority of the C. ancylus population was in the second larval instar in July, the third larval instar in August, the fourth larval instar in September, and the fifth larval instar from October through May. The spring population was 30% of the early instar maximum estimated the previous August. The spatial distribution of C. ancylus reflects a logarithmic pattern with early instar larvae more highly clumped than the late larval instar and pupal populations. Initial standing stock estimates were less than 1% of the standing stock biomass. A production estimate of 9.9 mg/m²·year (dry weight) was determined using the instantaneous growth method, Allen's Curve method, and the Hynes method of estimating secondary production. Turnover ratios (7.0 annual TR, 5.7 cohort TR) were higher than estimates reported as typical for benthic macroinvertebrates because of the low initial to final mean individual weight of the C. ancylus larvae (0.4%). Production estimates calculated for C. ancylus populations in waterwillow bed (4.4 mg/m²·year) and pool (13.7 mg/m²·year) habitats were less than calculated for the riffle population (19.9 mg/m²·year). The annual turnover ratio (10.2) was higher in the pool population than in other habitats because of spring larval migration into the pool from other habitats. A trend of higher production estimates with larger sized substrate particles and increased numbers of particles may reflect the increase in available food sources or attachment sites. The accuracy of production estimates and their applicability to water resource management may be limited by a failure to consider the spatial distributions of the population being sampled and the tendency for sampling procedures to be confined to single habitats.     

Growth and mortality of larval Myctophum affine (Myctophidae,Teleostei)

The growth and mortality rates of Myctophum affine larvae were analysed based on samples collected during the austral summer and winter of 2002 from south‐eastern Brazilian waters. The larvae ranged in size from 2·75 to 14·00 mm standard length (L_S). Daily increment counts from 82 sagittal otoliths showed that the age of M. affine ranged from 2 to 28 days. Three models were applied to estimate the growth rate: linear regression, exponential model and Laird–Gompertz model. The exponential model best fitted the data, and L₀ values from exponential and Laird–Gompertz models were close to the smallest larva reported in the literature (c. 2·5 mm L_S). The average growth rate (0·33 mm day^?1) was intermediate among lanternfishes. The mortality rate (12%) during the larval period was below average compared with other marine fish species but similar to some epipelagic fishes that occur in the area.     

Biology ofChironomus piger Str. (Diptera: Chironomidae) and its role in the self-purification of a river

Chironomus piger larvae are widespread in small rivers and canals strongly polluted with domestic sewage. Despite this, almost nothing is known concerning the biology of the species under natural conditions and its role in the process of river self-purification. For two years, benthic samples were collected in the Sestra River at a site about 250 m downstream of the effluent discharge drains of a sewage treatment installation where the greatest concentrations of the larvae occurred. The number and biomass ofC. piger larvae were subject to marked fluctuations,viz. 96,000–348,000 ind m^–2 and 420–1,800 g m^–2. 460 degreedays (on average) was required for development of one generation.C. piger has 5 or 6 generations per year depending on the hydrometeorological conditions during the growing season.C. piger larvae play an important role in self-purification of the river. They utilize precipitating seston for food and for building their dwelling tubes. According to our calculations the amount of organic matter assimilated in the area of maximum larval concentration ranged 80–177 g wet weight m^–2 day^–1, and 32–71 g wet weight m^–2day^–1 was mineralized.     

Larval fish distribution,growth and feeding in Patagonian fjords: potential effects of freshwater discharge

In fjord systems, freshwater inputs occur by ice melting and river discharge, affecting seawater salinity along fjord and adjacent waters, and potentially the ecology of early life stages of marine fish occurring in the area. During austral spring 2008, a bio-oceanographic cruise was carried out in southern Chile between 47°00′ and 50°09′S, an area influenced by Baker River discharge and ice melting of Northern and Southern Ice Fields, the largest glaciers from Patagonia. Surface salinity and temperature ranged from 1.22 to 32.80, and from 8.11 to 10.68°C, respectively. Larval lightfish Maurolicus parvipinnis (Sternoptychidae) and Falkland sprat Sprattus fuegensis (Clupeidae) were the dominant species, with abundances of 2.2–39.9 larvae 10 m⁻² and 3.4–77.1 larvae 10 m⁻², respectively. Postflexion stages of both species were collected mainly in surface density fronts. Otolith-based growth analyses estimated linear growth rates of 0.136 mm day⁻¹ for M. parvipinnis of 4.1–15.1 mm, and 0.448 mm day⁻¹ for S. fuegensis of 5.4–20.5 mm. Recent Otolith Growth Index (ROGI), based on the residual analysis of the relationship between increment width of outermost five microincrements and otolith radius, indicates that larval M. parvipinnis collected in low salinity waters showed a reduction of its recent growth rate compared those collected in saltier waters. Also, ROGI was positively correlated with salinity of the water column for larval M. parvipinnis. Gut content analysis showed that large larvae collected near sources of freshwater had lower number of prey in its guts and preyed on different items than fish larvae collected in saltier waters. Therefore, freshwater inputs from rivers and glaciers from Patagonia affected horizontal distribution, recent growth and feeding of larval fish in fjords and channels of southern Chile.     

Biological attributes of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin

Lake sturgeon Acipenser fulvescens are imperiled throughout the Laurentian Great Lakes basin. Efforts to restore this species to former population levels have been ineffective due in part to limited information regarding its early life history. The objectives of this study were to characterize the larval drift and biological attributes of age‐0 lake sturgeon in the lower Peshtigo River, Wisconsin. Lake sturgeon larvae were captured from May to June 2002 and 2003 using drift nets, while age‐0 juveniles were captured from June through October 2002 and 2003 using wading, snorkeling, backpack electrofishing, and haul‐seine surveys. Larval drift occurred within 14 days of adult spawning and extended from 1 to 3 weeks in duration, with two peaks in the number of fish drifting downstream each year. Larvae had a median total length (TL) of 19 mm (range: 13–23; N = 159) in 2002 and 18 mm (range: 13–24; N = 652) in 2003. Catch‐per‐unit‐effort for larvae was 0.18 fish h^?1 m² and 0.94 fish h^?1 m² in 2002 and 2003, respectively. Age‐0 juvenile lake sturgeon exhibited rapid growth (i.e. 2.57 mm day^?1 in TL and 0.66 g day^?1 in wet weight) throughout summer and fall months; relative condition of fish in both years was approximately 100, indicating good condition. Absolute abundance of age‐0 juveniles in 2003 was estimated at 261 fish using the Schnabel estimator. The results from this study indicate that the lower Peshtigo River contains important nursery habitats suitable for age‐0 lake sturgeon.