Backwater areas as nursery habitats for fishes in pool 13 of the Upper Mississippi River

Samples of larval and juvenile fishes were collected at two depths weekly during spring and summer 1983 near the mouths of backwater areas in Pool 13 of the Upper Mississippi River. The study was conducted to determine the relative value of these habitats as nursery areas for fishes present and to note any interactions that might occur between the backwaters which are being rapidly lost to siltation, and the main channel. The larvae and juveniles collected represented 13 families divided into 27 lower taxa. Cyprinidae, Clupeidae, and Sciaenidae made up 90% of the total catch. Both larvae and juveniles were more abundant near the surface than near the bottom. Densities differed greatly among the three backwater areas studied. Larval fishes were grouped on the basis of their relative abundance in the backwaters or main channel. Overall, more larvae were captured in the backwaters than in main-channel habitats, indicating that backwaters were more productive. In the main channel, densities were greater downstream from the mouths of the backwaters than upstream-possibly indicating that (1) larval fish drifted out of the backwater areas, (2) water rich in nutrients or zooplankton that flowed into the main channel created productive downstream sites that were used as nursery areas, or (3) adult fishes selected downstream sites as spawning areas. Juvenile forms were more abundant in the backwater areas then in the main-channel habitats, some bottom-dwelling fishes excepted. The backwater areas were judged to be important nursery areas for larval and juvenile fishes, and seemed to benefit downstream main-channel sites. Any loss of these habitats would be detrimental to the Mississippi River as a whole.     

Relative abundance of macroinvertebrates found in habitats associated with backwater area confluences in Pool 13 of the Upper Mississippi River

Ephemeroptera showed the greatest diversity and Diptera (due mainly to Chaoboridae) the greatest absolute abundance among the macroinvertebrate taxa collected in and near three backwater areas of the Upper Mississippi River from 24 April to 24 August 1983. Of the 32 taxa identified, all were insect larvae, pupae, or adults except for one amphipod and one copepod. Three peaks in total abundance were observed — a major one in late July and August and smaller ones in May and June. These peaks corresponded to periods of high temperatures and low flows. When the macroinvertebrates were divided into groups, depending on whether they were found predominantly in the backwater areas, in the main channel, or in a combination of the two, total densities were greater in the backwater areas than in either of the main-channel habitats. In the two main-channel habitats, densities were slightly greater downstream than upstream from the confluences of the backwaters with the main channel, possibly indicating that macroinvertebrates were drifting out of the backwater areas or that nutrients and zooplankton were drifting out of the backwater areas, increasing productivity in downstream areas.     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.     

The use of direct epifluorescent microscopy (DEM) and the direct epifluorescent filter technique (DEFT) to assess microbial populations on food contact surfaces

Two rapid methods, direct epifluorescent microscopy (DEM) and the direct epifluorescent filter technique (DEFT) on swab resuspension fluids, were compared with the traditional total viable count (TVC) on swab resuspension fluids for their ability to enumerate surface populations of attached bacteria. The degree of error in estimating surface populations was shown to be significantly less with DEM than DEFT followed by TVC. DEM estimated populations in the range 3 times 10³ to 5 times 10⁷ colonies/cm² whilst DEFT enumerated populations above 3 times 10⁴ colonies/cm² and TVC above 3 times 10⁵ colonies/cm² (as measured by DEM). Swabbing was shown to remove a constant proportion of organisms from the surface populations tested, although below 3 times 10⁵ colonies/cm² most of the organisms remained in the cotton matrix and were difficult to resuspend. DEFT was more able to enumerate swab resuspension fluids obtained from surface populations below 3 times 10⁵ colonies/cm² than was TVC.     

Autumn use of woody snags by fishes in backwater and channel border habitats of a large river

Snags are important to fish communities in small rivers and streams, but their importance to fishes in large rivers has not been investigated. This study examined snag use by fishes during autumn in backwater and channel border habitats in the upper Mississippi River, and compared these to fish communities in reference sites without snags. Species assemblages differed significantly between backwater and channel border habitats, and between snag and reference sites within the channel border, likely responding to differences in substrate, depth, and current velocity. In both habitats, average fish biomass and abundance were higher (2 to 50 ×) at snag sites than at reference sites, but these differences were significant only for channel border biomass. Fish taxa richness differed between backwater and channel border habitats, but not between snag and reference sites. Most large piscivorous fishes (e.g., Micropterus spp., Stizostedion spp.), several insectivorous fishes (Lepomis macrochirus, Ambloplites rupestris, Minytrema melanops), and a few prey fishes (L. macrochirus, Notropis atherinoides) were significantly more abundant at snag sites than at reference sites, suggesting active selection of snags for foraging or protection. Snag quality, as assessed by a snag rating index, had a direct effect on attracting fish communities with greater biomass, especially within the channel border habitat. These results indicate that snags are important habitat for fish communities in both backwaters and channel border habitats of the upper Mississippi River.     

Metabolic utilization of body stores during the early life of whitefish, Coregonus lavaretus L.

Patterns of oxygen consumption, ammonia and urea excretion were monitored during late embryogenesis, i.e. 5 days before mass hatching and 12 days during the free-swimming stage of whitefish larvae, Coregonus lavaretus. Oxygen consumption increased from 1.31 to 2.53 mgO₂ h⁻¹× 10³ eggs⁻¹ at hatching. Fasted, free-swimming larvae showed increasing oxygen consumption to the tenth day after hatching when it reached 5.52 mgO₂h⁻¹× 10³ larvae⁻¹. Ammonia and urea excretion increased during pre-hatching period from 52.1 to 163.2 and 26.8 to 51.4 μgh⁻¹× 10³ eggs⁻¹, respectively. The nitrogen excretion rate increased between the sixth and tenth day of fasting, i.e. for ammonia from 117.7 to 160.9 and for urea from 35.8 to 52.5 μg h⁻¹× 10³ larvae⁻¹. Cumulative data on nitrogen and energy metabolism indicated that during late embryogenesis, and up to the fifth day after hatching, protein dominated in the energy expenditure. During the free swimming stage, the ratio of fat to protein in energy expenditure rose from 0.86 to 1.99. Combined data for several fish species indicated high dependance of oxygen uptake during the hatching period on egg size and temperature.     

Isolation and phenotypical identification of spore-forming Bacillus species from Jordanian habitats with larvicidal activity against Drosophila melanogaster

Spore-forming Bacillus isolates were recovered from different Jordanian habitats. Of 37 samples, 187 colonies were selected. Forty-six (24·6%) of them were pathogenic to the third instar larvae of Drosophila melanogaster . Larvicidal activity of the isolates was from 0% (non-cultivated soil) to 83·3% (decomposed animal residues). The total spore count per gram weight varied from 0·1 × 10⁵–18 × 10⁵ among the 37 tested samples. Morphological and microscopical identification of the isolates showed the presence of 16 different Bacillus species. The pathogenic isolates were B. thuringiensis (44) and B. sphaericus (2).     

Experimental Infection of Nosema sp. Ghose in an Unnatural Host Lesioderma sericorne

ABSTRACT. Various doses of a microsporan parasite, Nosema sp., were fed to third and fourth instar larvae of Lesioderma sericorne that infested different types of stored grains. A spore dose of 3 × 10³ spores/individual resulted in a 39% infection rate, reduction in larval and adult weights, and mean spore concentrations of 1.28 ± 0.2 × 10⁸ spores/larva and 1.1 ± 0.2 × 10⁸ spores/adult. At the above dose, mortality was not well marked (about 35% in larvae and 25% in adults). At 3 × 10⁴ spores/individual, the rate of mortality increases to 80% in larvae and 60% in adults. However, more of the pest population (88% of larvae and 73% of adults) died at a dose of 3 × 10⁵ spores/individual. This dose produced mean spore concentrations of 3.91 ± 0.2 × 10⁸ spores/larva and 2.89 ± 0.2 × 10⁸ spores/adult. Insect death was caused by heavy damage to gut epithelia and fat bodies.     

Influence of woodlot floor topography on microbial decomposer distribution

The distribution of microbial populations that decomposed sugar, cellulose and lignin-related substrates was examined in a beech Fagus grandifolia Ehrh. and maple Acer saccharum Marsh. dominated woodlot developed on glacial till. The topography of the woodlot, characterized by rises, depressions and more extensive level areas about 1 m in diameter with a 0.5 m vertical maximum, produced a mosaic of decomposer habitats designated as high, level and low sites.
In general, populations of sugar, cellulose and lignin decomposing organisms (based on ten estimates made from April to October) were two to four times higher in litter and soil samples from low sites than those from high sites. Sugar decomposing bacteria in litter were most abundant at all topographic sites. 135 × 10⁶ g⁻¹ dry litter at high sites, 396 × 10⁶ g⁻¹ at level sites and 456 × 10⁶ g⁻¹ at low sites; lignolytic fungi were least abundant, 391 × 10² g⁻¹ dry litter at high sites. 700 × 10⁶ g⁻¹ at level sites and 954 × 10² g⁻¹ at low sites. Numbers of microbial decomposers in the topographic sites were correlated with organic matter content. Distribution of fungal genera did not appear to be related to topographic site. Most populations examined showed two numerical peaks, one in late May or June and one in late September or October. It is suspected that these peaks were influenced by the coincident timing of favourable physical conditions and priming by soluble nutrients leached from litter.     

Bacteriological study of shrimp, Penaeus monodon Fabricius, hatcheries in India

Shrimp hatcheries often face problems of mortality caused by diseases. To understand the bacteriological status of shrimp, Penaeus monodon Fabricius, hatcheries in India, a study of hatchery water at different points was conducted in several hatcheries located along the east and west coast of India. The species composition of the bacterial flora was also determined. The total plate counts of raw sea water on tryptic soya agar ranged from 10² to 10⁴ ml^–1, whereas it ranged from 10⁴ to 10⁶ ml^–1 in larval tanks. In the larval tanks, the proportion of Vibrio species ranged from 50% to 73%, as compared to 31% in raw sea water. A mixed bacterial flora was observed in hatchery water; however, in the larval tanks, the flora in the larvae was predominantly made up of Vibrio species. A few of the tested Vibrio isolates were non-virulent to shrimp larvae under experimental conditions. Over 90% of the strains were resistant to amoxycillin, ampicillin, cephalexin, cephazolin, cloxacillin and sulphafurazole. Most strains showed sensitivity to tetracycline, chloramphenicol, and quinolones such as norfloxacin and ciprofloxacin.     

Influence of habitat characteristics on small mammals in a Mexican high-altitude grassland

Small mammals in a high-altitude grassland area close to Mexico City were studied. Populations of 10 species were censused using live traps in 48 sample quadrats. Within each quadrat, vegetation characterization, including complete floristic listings, cover values for species and layers and values of habitat modification, were assessed. Habitats were described according to plant communities identified using ordination and classification methods. Nine different plant communities were obtained. Densities and abundance of all small mammal species were calculated for each of the habitats classified. Peromyscus alsloni was the most abundant species in all habitats, reaching maximum densities of 55 ha⁻¹ in pine forest with dense ground and herb layer. Peromyscus melanotis also occurred in all habitats but at lower densities (maximum 29 ha⁻¹). Reithrodontomys megalotis was found in all habitats except in tall dense grassland. Densities for this species were generally low (1-9 ha⁻¹) but reached 19 ha⁻¹ in short dense grassland. All other species were largely absent from 4–8 habitats and showed very low densities (0.75–4 ha⁻¹). The densities of the more abundant species were largely correlated with more open habitats and higher indices of habitat modification. Lower altitude grassland habitats have a greater abundance of small mammals and a higher species richness than the medium and higher altitude, physiognomically more complex habitats. Species richness was highest in tall pine-alder forest with a species-rich, dense herb layer and lowest in pine forest with dense ground and herb layers. Species richness was positively correlated with overall small mammal density.     

Production of amylase by the intestinal bacteria of Japanese coastal animals

H. SUGITA, J. KAWASAKI, J. KUMAZAWA AND Y. DEGUCHI. 1996. The amylase-producing ability of intestinal bacteria in one marine crab and seven fish species was determined. Mean total viable counts ranged from 1.3 × 10⁵ to 1.5 × 10⁸ cfu g⁻¹, and Vibrionaceae were predominant in all specimens. Of 1585 strains examined, 341 (21.5%) produced ≥0.01 U amylase ml⁻¹. Percentage of producers (≥0.01 U ml⁻¹) differed among genera/families. High abilities (≥0.05 U ml⁻¹) were found in 1.4-3.6% of Enterobacteriaceae, Pseudomonas and Vibrionaceae strains. On the other hand, percentage of producers varied with animal species. These results reveal that the amylase producers were widely distributed in the digestive tracts of coastal animals including crabs and fish, irrespective of their food habitats.     

Differing effects of suspended sediments on the performance of native and exotic Daphnia

1. Although large cladocerans are usually uncommon in large rivers, Daphnia lumholtzi (an exotic species in North America) is widespread and occasionally abundant. We collected zooplankton on the Illinois River (Illinois, U.S.A.) in 1995 and 1996 and found that the peak density of D. lumholtzi (25 L⁻¹) typically exceeded that of all native species combined. Maximum density occurred during warm periods (up to 27 °C) when concentrations of inorganic suspended sediments were high (>50 mg L⁻¹).
2. Using a life table experiment, we examined the effects of variation in suspended sediment (0 and 80 mg L⁻¹) and food (10⁴ and 10⁵ Ankistrodesmus cells mL⁻¹) on fitness of D. lumholtzi and the native Daphnia parvula. Daphnia lumholtzi had greater survivorship than D. parvula in most treatments and higher life-time fertility than D. parvula in all treatments. Both species achieved their fastest intrinsic rates of growth in treatments with high food, but their responses to suspended solids differed. The growth rate of D. lumholtzi in high food was slightly increased by higher turbidity, whereas that of D. parvula was depressed.
3. Results suggest that the ability of D. lumholtzi to tolerate suspended solids is an important factor contributing to its success in invading North American rivers.     

Sulphate-reducing bacteria in bovine faeces

Sulphate-reducing bacteria (SRB) were found in all of 200 bovine faeces examined. The number of SRB in bovine faeces ranged from 5 times 10² to 6 times 10⁸ bacteria g^-1. Of 50 isolates identified, all were assigned to the genus Desulfovibrio .     

Seasonal patterns of viruses, bacteria and dissolved organic carbon in a riverine wetland

SUMMARY 1. Viral and bacterial abundances were studied in relation to environmental attributes over an annual period, for both planktonic and attached (sediment, aquatic macrophyte and submerged wood) habitats, in a riverine wetland.
2. Annual mean abundance of planktonic viruses ranged from 2.3 × 10⁵−3.8 × 10⁵ particles mL⁻¹ and varied according to sampling site. Significant seasonal patterns in viral abundance were evident and appeared to be linked to variations in bacterial abundance, dissolved organic carbon and inorganic nutrients.
3. Annual mean abundance of viruses associated with surfaces ranged from 1.3 × 10⁶ particles cm⁻² on aquatic macrophytes to 1.1 × 10⁷ particles cm⁻² on wood and also showed seasonal patterns. The difference in viral dynamics among the different sites emphasizes the importance of considering habitat diversity within wetlands when examining microbial communities.     

Electrotransformation of meat lactobacilli. Effect of several parameters on their efficiency of transformation

Intact cells of several lactobacilli isolated from Spanish dry fermented sausages ( Lactobacillus curvatus, Lact. sake, Lact. plantarum and Lact. bavaricus ) were transformed by electroporation. With pNZ12 as a vector, transformation efficiencies of 2.4 times 10⁵, 3.8 times 10³ and 8.8 times 10² transformants μg^-1 DNA were observed for Lact. curvatus CTC435, Lact. sake CTC335 and Lact. bavaricus CTC232, respectively.
Effects of variation in experimental parameters on transformation efficiency were evaluated. Strains, vectors and buffers were the determinant parameters. The growth phase of the culture, cell concentration, voltage, use of cell wall weakening agents and the purity of the vector influenced the transformation efficiency in most strains.     

ESTIMATION OF PREY DENSITIES REQUIRED BY WESTERN NORTH ATLANTIC RIGHT WHALES

The apparent lack of significant recovery of western North Atlantic right whale populations may be related to the availability of prey in exploitable densities. We have attempted to estimate the concentration of zooplankton required by right whales to obtain a net energetic benefit over the long term, using estimated values for body weight, metabolic rate, assimilation efficiency, time spent feeding, mouth size and swimming speed. The estimated range of required energy densities is 7.57 to 2,394 kcal m⁻³ (3.17 × 10⁴ to 1.00 × 10⁷ joule m⁻³). These values are from one to more than three orders of magnitude greater than the densest concentration sampled in the vicinity of right whale aggregations in the Great South Channel. Right whales must seek out and exploit extremely dense patches of prey organisms in order to feed efficiently. The presence of such dense patches of zooplankton is likely to be a primary characteristic of spring, summer and fall right whale habitats.     

Diel and distributional abundance patterns of fish embryos and larvae in the lower Columbia and Deschutes rivers

Diel and distributional abundance patterns of free embryos and larvae of fishes in the lower Columbia River Basin were investigated. Ichthyoplankton samples were collected in 1993 during day and night in the main-channel and a backwater of the lower Columbia River, and in a tributary, the Deschutes River. Fish embryos and larvae collected in the main-channel Columbia River were primarily (85.6%) of native taxa (peamouth Mylocheilus caurinus, northern squawfish Ptychocheilus oregonensis, suckers Catostomus spp., and sculpins Cottus spp.), with two introduced species (American shad Alosa sapidissima and common carp Cyprinus carpio) comprising a smaller percentage of the catch (13.3%). Similarly, in the Deschutes River native taxa [lampreys (Petromyzontidae), minnows (Cyprinidae), and suckers Catostomus spp.] dominated collections (99.5% of the catch). In contrast, 83.5% of embryos and larvae in the Columbia River backwater were of introduced taxa [American shad, common carp, and sunfishes (Centrarchidae)]. In all locations, all dominant taxa except sculpins were collected in significantly greater proportions at night. Taxon-specific differences in proportions of embryos and larvae collected at night can in some instances be related to life history styles. In the main-channel Columbia River, northern squawfish and peamouth were strongly nocturnal and high proportions still had yolksacs, suggesting that they had recently hatched and were drifting downriver to rearing areas. In contrast, sculpin abundances were similar during day and night, and sculpins mostly had depleted yolksacs, indicating sculpins were feeding and rearing in offshore limnetic habitats. Taxon-specific diel abundance patterns and their causes must be considered when designing effective sampling programs for fish embryos and larvae.     

Effects of egg composition and prey density on the larval growth and survival of lake whitefish (Coregonus clupeaformis Mitchill)

Eggs were collected from two stocks of lake whitefish, Coregonus clupeaformis , in Lakes Michigan and Huron to assess the effect of egg composition and prey density on larval growth and survival. Egg composition parameters including wet weight (mg egg⁻¹), dry weight (mg egg⁻¹), percent water, total caloric content (cal egg⁻¹), caloric density (cal egg⁻¹), percent lipid content, and total lipidcontent (mg egg⁻¹) were measured. Fish hatched from six parental females in each stock were fed one of four rations (0, 18, 24, 50 brine shrimp larva⁻¹ day⁻¹) after yolk sac absorption. Length at hatch, endogenous growth, exogenous growth, and survival were measured during a 42-day laboratory experiment. Length at hatch of larvae was positively related to egg caloric content ( r ²=0.780). Endogenous growth for lake whitefish larvae was positively related to percent lipid content ( r ²=0.896) and total egg lipid content ( r ²=0.876) of parental females. Exogenous growth and survival of larval lake whitefish was positively related to prey availability. Larval fish growth was accurately modelled ( r ²=0.973) as a function of prey abundance using a threshold-corrected hyperbolic equation. These results indicate that both egg composition and prey availability have the potential to influence the growth and survival dynamics of larval lake whitefish significantly.     

Diel abundance, migration and feeding of fish larvae (Eleotridae) in a floodplain billabong

Eleotrid larvae (2.1–16 mm) were collected from surface waters of a billabong in south-eastern Australia. Estimates of larval density in plankton net samples at night averaged 148.3 larvae per m³ and 16.6 larvae per m³ during the day. In contrast, pump samples provided density estimates of 8.3 larvae per m³ at night and 0.9 larvae per m³ during the day. Larval densities did not differ between open water, snag (fallen tree) and Typha habitats, but Typha habitats yielded larger larvae than other habitats. 32.9% of larvae in pump samples were damaged and unmeasurable, creating a bias favouring larger larvae. The modal length of larvae in net samples at night was 5–6 mm, compared with 3–4 mm during the day, reflecting both greater net avoidance by larger larvae during the daytime and dispersal of smaller larvae from the surface at night. Dispersion patterns of larvae suggest that classes of larvae smaller than, and larger than 5.0 mm exhibit reciprocal diel vertical migration behaviour linked to ontogenetic changes in diet. Larvae less than 5 mm fed only during the day and preyed exclusively on rotifers, whereas larger larvae continued to feed at night and consumed mostly planktonic crustaceans.