Vulnerability of microcrustaceans to predation by the invasive filter-feeding mussel Limnoperna fortunei (Dunker)

Limnoperna fortunei is an Asian mussel introduced to South America around 1990. One of the most important impacts of this invader is probably its grazing on the plankton. In this study we evaluate the vulnerability of several planktonic microcrustaceans from the Paraná River floodplain to predation by adult L. fortunei. We conducted 2-h laboratory feeding experiments where the bivalves were offered microcrustaceans differing in overall body shape, size, and locomotive abilities. Ingestion and clearance rates for each taxon were estimated. Results suggest that, in addition to detritus and phytoplankton, microcrustaceans may be a very important food item for this invasive mollusc. Limnoperna fortunei can prey on larger organisms (up to 1100?µm) than Dreissena polymorpha, the European and North American invasive mussel.     

Predation and depth effects on abundance and size distribution of an invasive bivalve, the golden mussel Limnoperna fortunei, in a dam reservoir

We investigated the predation and depth effects on abundance and size distribution of an invasive freshwater bivalve, Limnoperna fortunei, post-larvae using screened (5-, 25-, and 50-mm mesh openings) and unscreened cages at three depths (6, 12, and 1 m above the bottom) in a dam reservoir, Lake Ohshio of Japan. The densities of L. fortunei on the unscreened cages were much lower than those of the 5-mm mesh screened cages at any depth. The predation rates estimated by dividing the density of the unscreened cage by that of the 5-mm mesh screened cage were 97.3% at 6 m depth, 96.6% at 12 m depth, and 95.8% at the bottom. Shell lengths of L. fortunei post-larvae were small on bottom cages, and their size distribution was significantly different from those at other depths. These results suggest that predation and depth affected the abundance and size distribution of L. fortunei in the lentic environment. The impact of L. fortunei invasion on the food web and the possibility of regulating their population by predation pressures are also discussed.     

Invasive mussels induce community changes by increasing habitat complexity

Habitat complexity is among the most important factors affecting the diversity, structure, and density of natural communities. The invasive byssate bivalves zebra mussel (Dreissena polymorpha (Pallas, 1771)) and golden mussel (Limnoperna fortunei (Dunker, 1857)) are sessile suspension feeders that form aggregations (druses), physically changing sediments and increasing habitat complexity, and providing shelter and food for other benthic organisms. In this study, we explored the impact of the change in habitat complexity on benthic community created by druses of L. fortunei and D. polymorpha, formed on various sediments. D. polymorpha was studied in Europe (Naroch Lake, Belarus) and in North America (Glen Lake and Lower Nashotah Lake, USA), and L. fortunei was studied in South America (Río Tercero Reservoir, Argentina). Druses of D. polymorpha or L. fortunei and samples of bare nearby sediment (without druses of exotic mussels) were collected at each sampling site. We found significant changes in species richness, density, biomass, taxonomic, and trophic structure of communities formed in druses compared to the nearby bare sediments. Community taxonomic richness increased threefold, and density increased sevenfold with increasing complexity of habitat from sand to druse. The feeding functional group approach indicated that the impact of increased complexity was reinforced by an increase in food supply in D. polymorpha and L. fortunei druses. Along with increasing species richness and densities, byssate bivalves homogenized benthic communities.     

Environmental modulation of reproductive activity of the invasive mussel Limnoperna fortunei: implications for antifouling strategies

Limnoperna fortunei (Dunker, 1857) (Bivalvia) invaded Argentina through the Río de la Plata estuary around 1990 and is presently established throughout five South American countries as a dominant component of the benthic fauna and a major nuisance for industry and power plants. Between 1997 and 2006 we monitored the reproductive activity of L. fortunei through weekly measurements of planktonic larvae in six South American water bodies: Río de la Plata estuary, Paraná and Carapachay rivers, Salto Grande, Itaipú and Embalse de Río Tercero reservoirs. Mean larval densities varied between 4000 and 7000 individuals m^?3; except in the reservoirs of Itaipú (450 ind. m^?3) and Salto Grande (869 ind. m^?3), where the mussel was first recorded shortly before our surveys, and upstream dispersal is limited (Salto Grande). In all cases, reproductive output decreases during the winter. At four of the six sites surveyed larval densities were comparatively high for 8.8–10.2 months per year. A lower food supply is possibly responsible for the shorter reproductive period of 5.9 months at Embalse. At Salto Grande, there is a well‐defined mid‐summer drop in larval numbers, coinciding with blooms of cyanobacteria. We propose that, in addition to temperature, two major factors may regulate the reproductive activity of L. fortunei: (i) the availability of food; and (ii) blooms of toxic cyanobacteria, significantly shortening the otherwise very long reproductive period. This information is important for the design of antifouling programmes involving the use of molluscicides, and has potential for reduced biocide use. These results provide supporting evidence for some fundamental ecological theories of invasions discussed here.     

A Study of the Chromatiaceae in a Saline Meromictic Lake in Saskatchewan,Canada

Lamprocystis roseopersicina was found to be the dominant phototrophic bacterium in meromictic Deadmoose Lake. Using carbon-14 it was determined that phototrophic bacteria fixed 14.3 g C m⁻² year⁻¹, 17.1 % of the total limnetic primary production. Experiments indicated low light intensities (X = 8.87 × 10⁻² cal cm⁻²hr⁻¹) to be the most important factor limiting bacterial production. Lamprocystis was shown to be capable of photoorganoheterotrophic uptake of glucose.     

A Quantitative Food Web Model for the Macroinvertebrate Community of a Northern German Lowland Stream

Trophic interactions and cycling of organic carbon within the macroinvertebrate community of a Northern German lowland stream were analyzed based on a compartment model. The network model describes the structure of the food web quantifying biomass, production, and consumption of their elements, of the entire system and between trophic levels. System primary production is 153.7 g C m⁻² yr⁻¹ and invertebrate production 53.3 g C m⁻² yr⁻¹. Invertebrate consumption amounts to 702.6 g C m⁻² yr⁻¹. Main flows are identified between trophic level 1 and 2 and are connected with highly productive compartments. ‘Anodonta and Pseudanodonta’ and Dreissena polymorpha show the highest consumption of all groups with 269.9 g C m⁻² yr⁻¹ and 114.1 g C m⁻² yr⁻¹, respectively. System consumption is highest on the import from the upstream lake with 532.5 g C m⁻² yr⁻¹, sediment detritus with 135.5 g C m⁻² yr⁻¹, and primary producers with 25.7 g C m⁻² yr⁻¹. The lowest predation pressure is observed for Bivalvia with an ecotrophic efficiency of <10% and highest for Chironomidae with 91%. Approximately 20% of organic matter entering the detritus pool are recycled to the living groups of the system. Transfer efficiencies between discrete trophic levels are generally low except for transfer of detrital material between level I and II.     

Episodic recruitment of the seedling banks in balsam fir and white spruce

• Premise of the study: In ecosystems where seed production is low and masting years are sporadic, or with species that have short-lived seeds, regeneration is assured by seedling banks rather than seed banks. Seedling establishment and survival play a critical role in determining the composition of these plant communities by supplying new individuals for their maintenance. Seedling emergence and mortality were investigated to test the hypothesis that recruitment into the seedling bank is periodic. • Materials and methods: Seed production and seedling emergence and survival was monitored during 1994-2007 in balsam fir (Abies balsamea) and white spruce (Picea glauca) in four pristine stands of the boreal forest of Quebec, Canada. Measurements were collected twice per month by sampling one permanent plot of 20 × 20 m per stand. • Key results: Seed-rain abundance reached 9 × 10³ seeds m⁻² year⁻¹, and was characterized by synchronous sequences of low and high seed production. New seedlings appeared only during the year following a seed production of at least 1 × 10³ and 1.5 × 10² seeds m⁻² year⁻¹ for balsam fir and white spruce, respectively. Seedlings emerged in July and survived 34-52 d on average, with balsam fir showing a longer lifespan and lower mortality, although 85–99% of seedlings died before completing one year of life. • Conclusions: The emergence of young seedlings was coupled with massive seed rains, which allowed synchronous replenishment of the seedling banks among stands and species, and generated different cohorts, yielding a discontinuous age structure.     

Transformation of the offshore benthic community in Lake Michigan: recent shift from the native amphipod Diporeia spp. to the invasive mussel Dreissena rostriformis bugensis

1. The native amphipod Diporeia spp. was once the dominant benthic organism in Lake Michigan and served as an important pathway of energy flow from lower to upper trophic levels. Lake‐wide surveys were conducted in 1994/1995, 2000 and 2005, and abundances of Diporeia and the invasive bivalves Dreissena polymorpha (zebra mussel) and Dreissena rostriformis bugensis (quagga mussel) were assessed. In addition, more frequent surveys were conducted in the southern region of the lake between 1980 and 2007 to augment trend interpretation. 2. Between 1994/1995 and 2005, lake‐wide density of Diporeia declined from 5365 to 329 m⁻², and biomass (dry weight, DW) declined from 3.9 to 0.4 g DW m⁻². The percentage of all sites with no Diporeia increased over time: 1.1% in 1994/1995, 21.7% in 2000 and 66.9% in 2005. On the other hand, total dreissenid density increased from 173 to 8816 m⁻², and total biomass increased from 0.4 to 28.6 g DW m⁻². Over this 10‐year time period, D. r. bugensis displaced D. polymorpha as the dominant dreissenid, comprising 97.7% of the total population in 2005. In 2007, Diporeia was rarely found at depths shallower than 90 m and continued to decline at greater depths, whereas densities of D. r. bugensis continued to increase at depths greater than 50 m. 3. The decline in Diporeia occurred progressively from shallow to deep regions, and was temporally coincident with the expansion of D. polymorpha in nearshore waters followed by the expansion of D. r. bugensis in offshore waters. In addition, Diporeia density was negatively related to dreissenid density within and across depth intervals; the latter result indicated that dreissenids in shallow waters remotely influenced Diporeia in deep waters. 4. With the loss of Diporeia and increase in D. r. bugensis, the benthic community has become a major energy sink rather that a pathway to upper trophic levels. With this replacement of dominant taxa, we estimate that the relative benthic energy pool increased from 17 to 109 kcal m⁻² between 1994/1995 and 2005, and to 342 kcal m⁻² by 2007. We project that previously observed impacts on fish populations will continue and become more pronounced as the D. r. bugensis population continues to expand in deeper waters.     

Effects of 254 nm UV irradiation on the mobility and survival of larvae of the invasive fouling mussel Limnoperna fortunei

In order to investigate the feasibility of using ultraviolet (UV) irradiation to prevent the invasive Asian mussel, Limnoperna fortunei, from colonizing components of the cooling systems of industrial and power plants, the mobility and mortality of its larvae were assessed after exposure to different doses of UVC (λ = 254 nm) in laboratory conditions. Total (100%) mortality was achieved with a dose of 149 mJ cm^?2 at 23?°C and 103 mJ cm^?2 at 25.8?°C. Immediately after exposure, larvae were alive but had reduced mobility. The proportion of active larvae increased after 24 h, but fell again at 48 and 72 h to levels similar to those immediately after exposure. The highest mortality rates were always recorded at the last observation, 72 h after exposure. These results indicate that the larvae of L. fortunei are highly sensitive to UVC, suggesting that UV irradiation has the potential to control fouling by this mussel when the water is relatively clear. However, application of UV-based technologies in plants that use cooling water from water bodies with high loads of suspended solids (eg the Paraná-Uruguay basin, with ca 160 mg l^?1 of suspended solids and absorbance values around 0.255) is unlikely to be effective without prior filtration of the water.     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.     

Byssal hairs in the invasive Asian freshwater bivalve Limnoperna fortunei (Mytilidae) in the Paraná River system with comments on this species in South America

We recorded, for the first time, byssal hairs in the Asian freshwater bivalve Limnoperna fortunei from the Paraná River system. We analysed the presence of hairs and their distribution on the shell in relation to habitat and shell size in 12 sites. Hairs were present in lentic habitats associated with macrophytes or organic matter, but were absent in lotic environments. The proportion of mussels with hairs was negatively correlated with current velocity. Hairs were more frequent and abundant in larger mussels. In general, the hairs are a similar length over the bivalve and almost entirely cover the shells in≥60% in lentic habitats. The projections allow L. fortunei to be camouflaged among the roots of macrophytes or coarse organic matter, assisting in avoiding visual predators. The clear-cut separation of L. fortunei populations into two different groups could be associated with phenotypic plasticity in this species.     

An Analysis of the Biotic Community in a Kumaun Himalayan Lake,Nainital (U. P.), India

A comprehensive study of phyto- and zooplankton and macrozoobenthic components in Lake Nainital showed that species richness was high for plankton and low for macrozoobenthos. The algal biomass was dominated by greens (54 %) and blue-greens (31 %), the zooplankton population by copepods (84 %), and the macrozoobenthic community by a Tubifex-Chironomus association constituting≥95 % of the annual number of the macrobenthic invertebrates. Respiration (807.5g C m⁻² year⁻¹) surpassed gross production (630.5 g C m⁻² year⁻¹). The mean annual ratio between phyto- and zooplankton biomass is 3.3 and between phytoplankton and herbivores it is 4.6. If biomass is treated as a measure of crude production, the relationship among the three trophic levels suggests that herbivory is inefficient while carnivory is efficient, because part of the primary production remains unutilized by dominant herbivorous zooplankters, whereas Mesocyclops leuckarti, the sole carnivore, feeds efficiently on rotifers and juveniles of other copepods. The low diversity of different biotic components and the P/R ratio of less than 1 perhaps suggest that the lake is passing through the stage of heterotrophic succession.     

Larvae of the invasive species <Emphasis Type="Italic">Limnoperna fortunei</Emphasis> (Bivalvia) in the diet of fish larvae in the Paraná River,Argentina

To assess the trophic impact of the planktonic larvae of the invasive Asian bivalve Limnoperna fortunei, introduced in South America around 1990, we investigated the gut contents of fish larvae collected at monthly intervals between October 2000 and March 2001 at three locations along a 600 km stretch of the Paraná River, and during November 2004 in two areas of marginal lagoons connected to the river near the city of San Nicolás, Argentina. Zooplankton was also collected in the lagoons in 2004. In total, 11,956 fish larvae were retrieved, of which 1,511 were used for detailed analyses. Of the 15 fish taxa collected, 11 had veligers of L. fortunei in their gut. Fish larvae with empty guts represented 60% (San Nicolás) to 72% (Paraná River) of the total number of fish. Proportions of feeding fish larvae with L. fortunei veligers in their guts varied between 20% (San Nicolás) and 56% (Paraná River); in 15% of the guts analyzed, L. fortunei was the only food item recorded. For those specimens that had consumed L. fortunei larvae and any other food item, L. fortunei was the most important item in 55% (Paraná River) to 71% (San Nicolás) of the animals in terms of biomass. No major temporal or spatial changes in the diet were observed along the Paraná River, but the relative biomass contribution of L. fortunei larvae differed strongly in fishes of different developmental stage. In protolarvae and mesolarvae, veligers accounted for 30–35% of the gut contents. In metalarvae, veligers accounted for only 3%, indicating enhanced food supply for the earliest fish life stages. Comparison of the relative proportions of the three main zooplankton types (L. fortunei veligers, cladocerans, and copepods) in the water and in larval fish guts indicates that L. fortunei is always selected positively over the other two prey types. While our results strongly suggest that the expansion of L. fortunei results in an enhanced food supply for local fish populations, they do not necessarily imply that the overall effect on the ecosystem in general, and on the fish fauna in particular is beneficial.     

Dispersion and Ecological Impact of the Invasive Freshwater Bivalve Limnoperna fortunei in the Río de la Plata Watershed and Beyond

Limnoperna fortunei is a freshwater bivalve that invaded South America through Río de la Plata estuary in 1989 and has since become a major macrofouling pest. Along the Paraná-Paraguay waterway, which hosts intense boat traffic, L. fortunei has moved upstream at an average rate of of 250 km per year. In contrast, along the Uruguay river, where boat traffic is restricted to the lowermost 200 km section, upstream colonization is almost 10-times slower. This suggests that attachment to vessels is by far the most important dispersion mechanism. It is suggested that the Amazon, Orinoco and Magdalena basins are under high risk of invasion by this mussel, especially through their estuarine gateways. All South American basins host innumerable water bodies with favorable conditions for L. fortunei’s colonization. Known ecological tolerance limits of the mussel also suggest that it may colonize much of the area from Central America to Canada, including waters that due to their low calcium contents, high temperature and pollution levels, and low oxygen are inadequate for the survival of Dreissena polymorpha. Despite it’s remarkable geographic expansion and its extremely high population densities, L. fortunei’s ecological effects have received very little attention so far. It is suggested that the 2.4-fold increase in Argentine landings of freshwater fish between 1992–1993 and 2000–2001 may be associated with the introduction of this prey species.     

Growth and annual production of the brown alga Laminaria religiosa introduced into the Uwa Sea in southern Japan

Recently, aquaculture of Laminaria japonica has expanded to the southern coast of Japan and to China along the East China Sea. The southerly distribution of L. religiosa, compared to that of L. japonica, indicated that the aquaculture of L. religiosa along the southern coasts of Japan might be feasible. Thus, we examined the growth, biomass and productivity of L. religiosa cultivated in the Uwa Sea, in southwestern Japan over a period of two years. The seawater temperature ranged from 12.9 to 27.4°C in 2003/2004 and from 12.2 to 28.3°C in 2004/2005. In 2003/2004, the maximum mean density, maximum mean length, and maximum mean wet weight of L. religiosa was 7.8 ± 5.0 ind. m⁻¹ (mean ± SD), 14.8 ± 4.6 cm, and 1.2 ± 0.8 g wet wt., respectively. In 2004/2005, no germination was confirmed through the study period. The maximum biomass and annual production in 2003/2004 were estimated to be 6.9 ± 5.2 g wet wt. m⁻¹ and 8.9 g wet wt. m⁻¹ year⁻¹, respectively. The present study revealed that L. religiosa cultivated in the Uwa Sea were much smaller compared with those of Hokkaido Island, where the alga is naturally found. For the growth of L. religiosa, a relatively long period of seawater temperatures below 13.5°C is required. In the study area, seawater temperatures were below 13.5°C only 11 days in 2003, and 12 days in 2004. As a result, it is thought that expanding the cultivation of L. religiosa to southern areas including the Uwa Sea will be difficult.     

Differences in larval dynamics of golden mussel <Emphasis Type="Italic">Limnoperna fortunei</Emphasis> between dam reservoirs with and without an aeration system

The golden mussel Limnoperna fortunei is a freshwater bivalve that adheres to water intake facilities, leading to problems of several kinds. Biofouling problems have been increasing recently in East Asia and South America, and the planktonic stage of this species is considered to play an important role in its dispersal. We investigated the larval dynamics of L. fortunei in two reservoirs, Lake Ohshio and Lake Takenuma, which are connected by a headrace channel. An aeration system for water quality conservation was present in the former reservoir but not in the latter. Larval density in Lake Ohshio was more than 10,000 individuals/m³ with a maximum of 80,000 individuals/m³ in summer. The density in Lake Takenuma was much lower, with a maximum of around 200 individuals/m³. Water temperature (WT) and dissolved oxygen (DO) concentration were almost uniform regardless of water depth in Lake Ohshio because of destratification due to continuous aeration. Summer WT and DO in the lake were considered to be suitable for survival and reproduction of L. fortunei. On the other hand, stratification was found for WT and DO in Lake Takenuma throughout the summer. The low WT and DO found in the deep areas of the lake in summer were considered to be not suitable for survival and reproduction of this species. Thus, the population of L. fortunei larvae differed widely even in two adjoining lakes, and WT and DO are considered to be critical factors, especially for reproduction.     

Contribution of terrestrial invertebrates to the annual resource budget for salmonids in forest and grassland reaches of a headwater stream

1. The annual input, contribution to the diet of salmonids, and quantitative input of terrestrial invertebrates to four reaches with contrasting forest (n=2) and grassland riparian vegetation (n=2) were compared in a Japanese headwater stream.
2. The annual input of terrestrial invertebrates falling into the forest reaches (mean±1 SE=8.7×10³±0.3×10³ mg m^?2 year^?1) was 1.7 times greater than that in the grassland reaches (5.1×10³±0.8×10³ mg m^?2 year^?1), with clear seasonality in the daily input of invertebrates in both vegetation types. The daily input, however, differed between the vegetation types only in summer, when it rose to a maximum in both vegetation types.
3. Fish biomass also differed among the seasons in both vegetation types, being less in the grassland reaches. The contribution of terrestrial invertebrates to the salmonid diet in the forest and grassland reaches was 11 and 7% in spring, 68 and 77% in summer, 48 and 33% in autumn, and 1 and 1% in winter, respectively. The prey consumption rate of fish, which was similar between the vegetation types, increased with stream temperature and was highest in summer. Terrestrial invertebrates supported 49% (mean±1 SE=5.3×10³±0.4×10³ mg m^?2 year^?1) of the annual, total prey consumption (10.9×10³±1.7×10³ mg m^?2 year^?1) by salmonids in the forest and 53% (2.0×10³±0.3×10³ mg m^?2 year^?1) (3.8×10³±0.6×10³ mg m^?2 year^?1) in the grassland reaches.
4. Salmonids were estimated to consume 51 and 35% of the annual total (falling plus drift) input of terrestrial invertebrates in the forest and grassland reaches, respectively. The input of terrestrial invertebrates by drift, however, was almost equal to the output in both vegetation types, suggesting that the reach‐based, in‐stream retention of terrestrial invertebrates almost balanced these falling in.
5. Difference in the riparian vegetation, which caused spatial heterogeneity in the input of terrestrial invertebrates, could play an important role in determining the local distribution of salmonids.     

The productivity and composition of mangrove forests,Laguna de Términos,Mexico

The composition and productivity of two mangrove sites surrounding the Laguna de Términos, Mexico, were studied from March 1979 to January 1984. Measurements were made of the tree composition, above-ground woody biomass changes, and litterfall production at a high-salinity fringing site and a low-salinity riverine site. Rhizophora mangle L. was the dominant tree at the fringing site, but occurred only at the water's edge at the riverine site. Avicennia germinans L. dominated the inland area of the riverine site. Laguncularia racemosa Gaertn. f. had a more even distribution from shore to inland and from site to site. Average diameter at breast height (DBH) was greater at the riverine site for each of the three species; however, tree density (trees > 2.5 cm DBH) was more than twice as high at the fringing site (7510 ha⁻¹) than at the riverine site (3360 ha⁻¹). Wood production (1206 g m⁻² year⁻¹ vs. 772 g m⁻² year⁻¹) and litterfall (1252 g m⁻² year⁻¹ vs. 835 g m⁻²) were higher at the riverine site than at the fringing site. Total estimated above-ground net production was 2458 g m⁻² year⁻¹ at the riverine site and 1607 g m⁻² year⁻¹ at the fringing site.     

Toxic Microcystis (cyanobacteria) inhibit recruitment of the bloom‐enhancing invasive bivalve Limnoperna fortunei

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Growth performance of juvenile Russian sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) at two stocking densities in net cages

The growth performance of juvenile sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) was studied in experimental net cages (2 m × 2 m × 2 m) in freshwater Sapanca Lake. Fertilized eggs were imported from Krasnodar, Russia in January 2001. Two experimental stocking densities were employed (12 and 8 ind. m⁻³). Sturgeon were hand‐fed a pelleted commercial trout feed twice daily throughout the 203‐day experiment period. Fish were grown at ambient temperature (12.7–28.5°C) and natural photoperiod. Initial and final mean body weights were 279.5 g (±31.27) and 1112.8 g (±234.77) in the first group, and 271.1 g (±28.21) and 1140.5 g (±213.31) in the second group, respectively. Results were a fourfold biomass density increase in both trials from an initial 3.48 to 12.4 kg m⁻³ (high density) and 2.2 to 8.8 kg m⁻³ (low density). Mean specific growth rate (SGR) was determined as 2.69% day⁻¹ in both groups. Mean condition factor (CF) at the end of the experiment was 0.36 ± 0.05 in the high‐density group and 0.41 ± 0.05 in the low‐density group. Mean feed conversion ratio (FCR) was calculated to be 5.7 and 5.8, respectively. Survival was 92.7% in the first group (high density) and 96.1% in the second group (low density). The results demonstrated that sturgeon juveniles can be raised in cages and that growth performance (CF, SGR and FCR) and mortality of sturgeon were not significantly different at the two stocking densities (P > 0.05) tested.