Tubifex Research Articles

Monitoring the sensitivity of the oligochaete Tubifex tubifex in laboratory cultures using three toxicants

Acute toxicity tests were conducted to assess the sensitivity of laboratory cultured Tubifex tubifex (Annelida, Clitellata), as an intralaboratory quality assurance requirement for the test organisms used in sediment chronic bioassays. Worms were exposed to cadmium, copper, and chromium in water-only 96-h tests, in single metal exposure, over a three-year period. The lethal concentration for the x% of the exposed population (LCx), the No-Observable-Effect Concentration (NOEC) and the Lowest-Observable-Effect Concentration (LOEC) were estimated. Based on LC50 values, the rank of toxicity was Cu+2>Cd+2>Cr+6. Sensitivity remained relatively constant during the research period and was comparable with the sensitivity of the same culture stock examined more than 10 years ago. This observed consistency in sensitivity indicates that comparisons between different sediment chronic bioassays conducted during the study period, using T. tubifex worms from the same culture stock, was appropriate. It is necessary to control both worm biomass and age for the acute test in order to standardize the test-organism conditions in intralaboratory quality assurance programs.

Effects of uranium-contaminated sediments on the bioturbation activity of Chironomus riparius larvae (Insecta, Diptera) and Tubifex tubifex worms (Annelida, Tubificidae)

Freshwater sediments represent a compartment for accumulation of toxic substances, notably of metallic pollutants such as uranium. However, they also constitute a privileged habitat for many benthic macro-invertebrate species with important roles in the functioning of these ecosystems, particularly through their bioturbation activities. Uranium accumulation in sediments can thus have harmful effects on these organisms (e.g., developmental delay, malformations, mortality). The present study aimed to evaluate the consequences of these effects on the bioturbation activity of Chironomus riparius larvae and Tubifex tubifex worms. These two species, which are widespread in freshwater ecosystems, are characteristic of two different modes of bioturbation: bioirrigation and upward bioconveying, respectively. By quantifying the burial and redistribution of fluorescent particulate tracers (microspheres), sediment reworking induced by these macro-invertebrates was measured after 12 d of exposure. Biodiffusion D b and bioadvection W rates, as well as several other parameters, were estimated to assess and compare the bioturbation activity of the two species, separately and in combination, between uncontaminated and uranium-spiked sediments. The results reveal that C. riparius larvae were more sensitive to uranium, but their bioturbation activity, even under uncontaminated conditions, had little effect on sediment reworking. Particle mixing was mainly induced by T. tubifex worms, which were only affected by uranium at high concentrations in the sediment. Finally, bioturbation by T. tubifex led to a high degree of uranium release from sediment to the overlying water, which highlights the crucial role of this mostly dominant species on uranium biogeochemical cycles at concentrations existing in naturally contaminated sites.

Growth, fat content and fatty acid profile of South American catfish, surubim (Pseudoplatystoma fasciatum) juveniles fed live, commercial and formulated diets

Summary South American catfish, barred surubim (Pseudoplatystoma fasciatum) juveniles (117.6 ± 11.8 mg individual weight; 28.3 ± 2.5 mm total length) were fed various diets: one live (Tubifex worms), two commercial (Aglo Norse and Bio Kyowa), and one semi-purified formulated diet (75% peptide based protein) over a 2-week period. Fish fed the Aglo Norse diet showed the highest growth performance, but cannibalism also was very high (42%). Fish fed peptide based formulated diet demonstrated the lowest growth rate, with no cannibalism. The highest survival was achieved with fish fed Tubifex worms (100%). Lipid level in the whole body of the fish fed four different experimental diets did not differ significantly, averaging 3.6 ± 0.7%. Fatty acid composition of neutral and phospholipid fractions of whole body lipids of fish reflected the fatty acid composition of the diets. The high level of 20:4n-6 in Tubifex worms resulted in a high level of this fatty acid in the tissue of fish fed this diet. It remains uncertain how high survival and no cannibalism is related to dietary lipids/fatty acids. In all cases, the increasing ratio of n-3 HUFA (highly unsaturated fatty acids)/n-6 HUFA in phospholipid fractions suggested the elongation and desaturation of 18:3n-3 to 22:6n-3 via 20:5n-3. Moreover, in respect to the 20:4n-6 levels in the diets, an increase in the concentration of this fatty acid in phospholipid fraction suggests that South American catfish can transform linoleate into arachidonate.

Ecotoxicity of uranium to Tubifex tubifex worms (Annelida, Clitellata, Tubificidae) exposed to contaminated sediment

In freshwater ecosystems, sediments act as an accumulation compartment for metallic pollutants as uranium. However, they are also the habitats of numerous benthic macroinvertebrates that directly influence the structure and functioning of such environments. Consequently, these organisms could be affected by uranium. This laboratory study aimed to assess the ecotoxicity of uranium on Tubifex tubifex through 12-day exposure to contaminated sediment (0–5980 μg U g −1 dry wt). At high concentrations (>599 μg U g −1 dry wt), malformations were observed, and survival, biomass and burrowing activity were all reduced. This relative high resistance in polluted environments can be explained mainly by the implementation of several processes as autotomy, regeneration ability, increased production of mucus, a hormetic effect on biomass and a probable strategy for avoiding the contaminated sediment. This study represents the first assessment of uranium impact on T. tubifex at realistic concentrations in sediments near mining sites.

Efficacy of different types of live and non-conventional diets in endangered clown knife fish Chitala chitala (Hamilton-Buchanan) during its early life stages

In the present study, the growth and survival of early life stages (ELS) of Chitala chitala were studied in nylon hapa for 28 days, followed by rearing in fibreglass reinforcement plastic (FRP) tanks for a period of 30 days. Ten-day-old ELS of C. chitala reared in hapa were fed with three different diets namely Indian Major Carp (IMC) spawn (<8 mm), live tubifex and fresh fish eggs. In the second phase, 28-day-old ELS were stocked in 200-lit FRP tank and supplied four different live diets namely live tubifex worm, chironomous larvae, zooplanktons and mosquito larvae. Fish accepted all types of diets in the experimental rearing period in both the systems. The experiments conducted in hapa showed a higher specific growth rate (SGR), weight gain per cent and survival rate in larvae fed with live tubifex (SGR=1.76±0.02) than fish eggs (0.77±0.31) and IMC spawn (0.46±0.12). The study carried out in FRP tanks revealed that SGR was higher in ELS fed on chironomous larvae (4.44±0.61), followed by mosquito larvae (3.29±0.40) and live tubifex (3.28±0.36), whereas minimum SGR was recorded with zooplanktons (2.84±0.66). A significant difference (P<0.05) in SGR, final mean weight and weight gain (%) was also recorded. The highest mean survival rate (100%) of ELS in an FRP tank was observed in chironomous larvae and zooplanktons, whereas with live tubifex and mosquito larvae the same survival rate (80%) was recorded. The rate of survival of the ELS reared in hapa varied from 65% to 85%. The experiments showed that ELS of C. chitala could be reared successfully in hapas and fibreglass reinforcement tanks for attaining better survivability and growth.

Reusing of Organic Waste from Tubifex sp. Substrate in nature

&lt;p&gt;This study was conducted to determine whether organic waste from the substrate of &lt;em&gt;Tubifex&lt;/em&gt; sp. can be used as inoculants to produce them through culture. Substrate used was the mix of mud and chicken manure by ratio of 1:1, placed on the container 80×20×15 cm, water elevation 2 cm, and water debit 300 ml/min. Inoculants number was ranged from 57 to 60 Tubifex sp. per container. The length of Tubifex sp. body was ranged from 0.9 to 3.5 cm and an individual mean weight of 2.78 mg. Organic waste applied was 500 g, 1000 g, and 1500 g. Rearing was performed for 50 days. During experiment chicken manure of 0.075 g/m&lt;sup&gt;2&lt;/sup&gt; was added into culture every day. The results of study showed that higher population of Tubifex sp. (174,227 tails/m&lt;sup&gt;2&lt;/sup&gt;; 413.7 gram wet weight) was obtained by using 1000 g of organic waste. Thus, organic waste derived from the substrate of Tubifex sp. from the nature can be reused to culture Tubifex sp. at the controlled container.&lt;/p&gt; &lt;p&gt;Keywords: &lt;em&gt;Tubifex&lt;/em&gt;, organic waste, population&lt;/p&gt; &lt;p&gt;&lt;em&gt; &lt;/em&gt;&lt;/p&gt; &lt;p&gt;ABSTRAK&lt;/p&gt; &lt;p&gt;Penelitian ini dilakukan untuk mengetahui apakah limbah organik sisa hasil penangkapan cacing sutera dari alam dapat digunakan sebagai inokulan untuk memproduksi cacing sutera melalui kegiatan budidaya. Substrat yang digunakan berupa campuran lumpur dan kotoran ayam dengan perbandingan komposisi masing-masing 1:1, ditempatkan dalam wadah berukuran 80×20×15 cm, debit air 300 ml/menit/wadah, dan tinggi air 2 cm. Jumlah cacing yang ditebar antara 57 - 60 ekor, panjang cacing 0,9 - 3,5 cm, dengan bobot individu rata-rata 2,78 mg. Limbah organik sebagai inokulan awal cacing sutera masing-masing seberat 500 g, 1.000 g dan 1.500 g. Pemeliharaan dilakukan selama 50 hari. Selama pemeliharaan dilakukan pemupukan menggunakan kotoran ayam sebanyak 0,075 g/m&lt;sup&gt;2&lt;/sup&gt; setiap hari. Hasil penelitian menunjukkan bahwa populasi cacing tertinggi diperoleh dengan menggunakan limbah organik sebanyak 1.000 gram (174.227 ekor/m&lt;sup&gt;2&lt;/sup&gt;; 413,7 g). Dengan demikian, limbah organik substrat cacing sutera dari alam dapat digunakan kembali untuk budidaya cacing di wadah terkontrol.&lt;/p&gt; &lt;p&gt;Kata kunci: &lt;em&gt;Tubifex&lt;/em&gt;, limbah organik, populasi&lt;/p&gt;

Effects of chitosan on oxidative stress and metallothioneins in aquatic worm Tubifex tubifex (Oligochaeta, Tubificidae)

Chitosan is a natural polymer which has the property to elicit the natural defenses mechanism in plant and which can be an interesting biopesticides. It is then necessary to investigate the potential toxicity of chitosan for aquatic animal health. Metallothioneins (MTs) are low molecular weight proteins, mainly implicated in metal ion detoxification. Increase in MTs contents had been considered as a specific biomarker of metal exposure. However recently it has been demonstrated that MTs participate in several cellular functions such as regulation of growth and anti-oxidative defenses. Therefore, the induction of MTs has been investigated in the aquatic worms Tubifex tubifex exposed to chitosan. MTs levels in exposed worm increased significantly ( p > 0.05) after 2, 4, and 7 days of exposure to different concentrations of chitosan (maximum + 158.19 ± 10.2% after 2 days of exposure to 125 mg l −1 of chitosan). Several antioxidant parameters including glutathione (GSH), glutathione- S-transferase (GST), glutathione reducatse (GR), and catalase (CAT) were quantified in T. tubifex after 2, 4, and 7 days of exposure to chitosan. Exposure to chitosan had a negative effect on T. tubifex growth (maximum effect −6.11 ± 1.6% after 7 days with 125 mg l −1) demonstrating the toxic effect of the pesticide. This growth rate decrease was accompanied by a reduction in protein contents. The activity of catalase (CAT), glutathione- S-transferase (GST), and glutathione reductase (GR) increased in response to the chitosan demonstrating an oxidative stress in the worms.

Heavy Metal Concentrations in Water, Sediments and Body Tissues of Red Worm (Tubifex spp.) Collected from Natural Habitats in Mumbai, India

Live feeds, especially Tubifex spp., which are collected from a wide variety of polluted habitats, are used by aquarium fish keepers in India. These habitats receive domestic sewage and industrial wastes from nearby residential and industrial areas. Reports of morbidity and mortality from aquarium fish culturists in and around Mumbai led to the present investigations on the ecology of these habitats with a view to assess the water quality, presence of heavy metals in the environment and their bioaccumulation in Tubifex worms, and to examine whether these habitats could be exploited to meet the demand of the industry. Six natural red worm (Tubifex spp.) collection centres in Mumbai and Thane districts of Maharashtra state in India constituting a major source of live Tubifex supply to aquarium fish industry were evaluated for pollution, heavy metal concentration in water, sediments and in the body tissues of Tubifex. Data revealed the presence of heavy metals in water and sediments at collection sites and bioaccumulation of cadmium, iron, lead, zinc and copper in body tissues of Tubifex worms. Cadmium ranged from 2.38 to 7.21 mg/kg, iron 671.9 to 5738 mg/kg, lead 14.95 to 33.49 mg/kg, zinc 60.20 to 166.60 mg/kg and copper 29.38 to 108.90 mg/kg of dry Tubifex worms. The study suggests that all the six collection sites are polluted and the red worms contaminated with heavy metals and hence, unfit for use in aquaria or feeding any variety of fish or crustaceans in the hatcheries.

Sound production, hearing and possible interception under ambient noise conditions in the topmouth minnow Pseudorasbora parva

Sounds were produced by the topmouth minnow Pseudorasbora parva, a common Eurasian cyprinid, during feeding but not during intraspecific interactions. Feeding sounds were short broadband pulses with main energies between 100 and 800 Hz. They varied in their characteristics (number of single sounds per feeding sequence, sound duration and period, and sound pressure level) depending on the food type (chironomid larvae, Tubifex worms and flake food). The loudest sounds were emitted when food was taken up at the water surface, most probably reflecting ‘suctorial’ feeding. Auditory sensitivities were determined between 100 and 4000 Hz utilizing the auditory evoked potentials recording technique. Under laboratory conditions and in the presence of natural ambient noise recorded in Lake Neusiedl in eastern Austria, best hearing sensitivities were between 300 and 800 Hz (57 dB re 1 μPa v. 72 dB in the presence of ambient noise). Threshold‐to‐noise ratios were positively correlated to the sound frequency. The correlation between sound spectra and auditory thresholds revealed that P. parva can detect conspecific sounds up to 40 cm distance under ambient noise conditions. Thus, feeding sounds could serve as an auditory cue for the presence of food during foraging.

Performance of different types of diets on experimental larval rearing of endangered Chitala chitala (Hamilton) in recirculatory system

This is the first report on the successful larval rearing of captive bred population of Chitala chitala (Hamilton). C. chitala is one of the endangered fresh water fish species in India for which the development of controlled larval rearing procedures are needed for stock enhancement. Fifteen days old post-hatchlings were stocked for 28 d in a 30 L recirculatory tanks using eight different diets i.e. live feed (tubifex worms, chironomous larvae, zooplanktons,), dry feed (dry tubifex, spirulina, daphnia) and other non-conventional feed (fish eggs and boiled egg-yolk). Fishes accepted all types of diets. The study revealed that specific growth rate (SGR) was higher in post-hatchlings fed on live tubifex worms (2.40 ± 0.72) followed by fish eggs (2.15 ± 0.71), dry tubifex (2.12 ± 0.40), chironomous larvae (1.91 ± 0.44), spirulina (1.79 ± 0.38), daphnia (1.42 ± 0.79) and planktons (1.37 ± 0.77) whereas minimum SGR was recorded with boiled egg-yolk (0.63 ± 0.5). A highly significant difference ( p < 0.01) in SGR was observed in fish fed on live feed (tubifex worms, chironomous larvae, planktons, spirulina), dry tubifex and fish eggs whereas for daphnia and boiled egg-yolk it was only significant ( p < 0.05). The final mean weight and weight gain showed highly significant difference ( p < 0.01) in live tubifex, zooplanktons, spirulina, chironomous larvae, dry tubifex and fish eggs, whereas daphnia and boiled egg-yolk fed larvae showed significant difference ( p < 0.05). Highest mean survival rate on day 28 was observed in live tubifex worms (94%) and chironomous larvae (92%). The post-hatchlings reared with spirulina and daphnia showed same survival rate of 88% whereas the lowest mean survival of 66% was recorded in boiled egg-yolk. The experiments showed that captive bred post-hatchlings of C.chitala could be reared in experimental recirculatory system for attaining higher growth and survival during early life stages. However, methods to improve the larval rearing have to be improved further for commercial farming of the species.

Behavioural responses of two popular ornamental carps, Cyprinus carpio L. and Carassius auratus (L.), to monoculture and polyculture conditions in aquaria

Experiments were conducted to document behavioural responses of koi carp, Cyprinus carpio L., and goldfish, Carassius auratus (L.) to monoculture and polyculture conditions in aquaria. Two parallel experiments, otherwise involving similar experimental protocols, were carried out with two batches of fish, fed with live tubifex worm (first batch) and live zooplankton (second batch). Each of the trials, randomized with respect to treatment, yielded data on aggressive encounters (chases, nips), both in presence and absence of food. The two species exhib- ited considerable variation in the extent and type of aggression displayed, koi carp being the more aggressive species. Frequency of attack increased in the presence of food. The impact of aggressive behaviour of koi carp was conspicuous by the increased level of attack on goldfish in polyculture trials in both experimental batches.

Metallothioneins induction and antioxidative response in aquatic worms Tubifex tubifex (Oligochaeta, Tubificidae) exposed to copper

Metallothioneins (MTs), are low molecular weight proteins, mainly implicated in metal ion detoxification. Increase in MT contents is considered as a specific biomarker of metal exposure. Recently it has been demonstrated that MTs participate in several cellular functions such as regulation of growth, and antioxidative defences. Tubifex tubifex were exposed to different copper concentrations (50, 100, and 200 μg l −1) for 7 and 15 days. MT levels in exposed worms increased significantly ( p < 0.05) after 7 and 15 days of exposure to different concentrations of copper (maximum +208% for 100 μg l −1 after 7 days of exposure). Also important perturbation in metal–metallothionein content occurred, along with an increase in total soluble protein content in all treated worms after 7 and 15 days (max. +88.49%). Catalase activities (CAT) in Cu treated-worms were significantly increased, and demonstrated a development of antioxidative defenses. Additionally a reduction of gulathione-S-transferase (GST) was observed in all treated worms after 7 days of exposure to Cu (max. −44.42%). The high induction of MTs observed during T. tubifex exposure to Cu make them potentially useful biomarkers to monitor metal pollution.

Water Temperature Affects a Host–Parasite Interaction: Tubifex tubifex and Myxobolus cerebralis

AbstractThe aquatic oligochaete worm Tubifex tubifex is an obligate host of Myxobolus cerebralis, the causative agent of salmonid whirling disease. Tubifex tubifex becomes infected by ingesting M. cerebralis myxospores and releases triactinomyxons (TAMs) into the water that then infect salmonids. In a laboratory experiment, we examined how water temperature influenced changes in oligochaete population size and biomass and the release of TAMs in three genetically identified strains of T. tubifex when exposed and not exposed to M. cerebralis myxospores. Increases in population size and biomass were greatest at 8.0°C for the Gallatin River strain, greatest at 15.0°C for the Madison River strain, and similar at both temperatures for the Mt. Whitney strain. After exposure to M. cerebralis myxospores, Mt. Whitney and Madison River T. tubifex both released TAMs at 15°C beginning on day 88 and at 8.0°C on day 169 (Mt. Whitney strain) and day 182 (Madison River strain); thus, between 1,320 and 1,456 degree‐days were required for M. cerebralis to develop. Gallatin River T. tubifex did not release TAMs. We found no evidence that M. cerebralis developed differently in strains of T. tubifex with different temperature requirements; therefore, it appears that temperature‐driven parasite development rates are a primary determinant of the timing of TAM release.

Effects of the Herbicide Isoproturon on Metallothioneins, Growth, and Antioxidative Defenses in the Aquatic Worm Tubifex tubifex (Oligochaeta, Tubificidae)

Metallothioneins (MTs) are low molecular weight proteins, mainly implicated in metal ion detoxification. Increase in MT contents is considered to be a specific biomarker of metal exposure. Recently it has been demonstrated that MTs participate in several cellular functions such as regulation of growth, and antioxidative defenses. Therefore, the induction of MTs as biomarkers of exposure to the pesticide isoproturon has been investigated in the aquatic worms Tubifex tubifex. MT levels in exposed worms increased significantly (p < 0.05) after 2, 4, and 7 days of exposure to different concentrations of isoproturon (maximum increase compared to unexposed controls: +148.56% for 10 mg l(-1) after 4 days of exposure). In response to isoproturon, the activity of glutathione-S-transferase (max. +52%), glutathione-reductase (max. +100%), and catalase (max. +117%) increased, demonstrating the occurrence of an oxidative stress response to the herbicide. Thus, the increase in MT contents caused by isoproturon was interpreted as a defense response towards increased oxidative stress generated by the herbicide. Residues of isoproturon and its metabolites, 1-(4-isopropylphenyl)-3-methylurea, 1-(4-isopropylphenyl) urea, and 4-isopropylanilin were detected in the worm growth medium. Half-life of the herbicide was shorter at a low (0.1 mg l(-1)) initial concentration. The herbicide accumulated in T. tubifex but no metabolite could be detected.

Metallothionein induction in aquatic oligochaete tubifex tubifex exposed to herbicide isoproturon.

Metallothioneins (MTs) are low-molecular-weight proteins mainly involved in metal ion detoxification. Recently it has been demonstrated that MTs participate in several cellular functions such as regulation of growth and antioxidative defenses. Moreover, pesticides can induce their synthesis. The aim of the current work was to determine the effects of isoproturon, either pure or formulated as Matin (suspension containing an isoproturon concentration of 500 g. L(-1)), on the metallothionein and total protein contents of the aquatic worm Tubifex tubifex. MT levels in exposed worms increased significantly after 7 and 15 days of exposure to a concentration of the herbicide of 50 mg. L(-1). Isoproturon reduced the metal (Cu, Zn, and Cd) content of metallothioneins, and it also increased the total protein content of the worms. These results suggest that MT induction may not be considered a specific biomarker of metal exposure but that it can be used as a nonspecific biomarker of the effect of isoproturon effect in aquatic worms.

Live And Inert Foods For Postlarvae Of The Giant Freshwater Prawn Macrobrachium Rosenbergii

Five live or inert food organisms (adult Artemia, Moina, Tubifex worms, clam meat, poultry egg custard) were evaluated as feed for postlarvae of Macrobrachium rosenbergii. The postlarvae (avg 5.2±0.22 mg, 7.2±0.38 mm) were reared in plastic pools (0.9 m diameter x 0.6 m) contain- ing 100 l fresh water, stocked at one postlarva per liter for 30 days, with five replicates of each treatment. There were significant differences (p&lt;005) in final weight gains of the postlarvae (62.94-88.86 mg), final length gains (16.45-20.71 mm) and survival (69.67-92.33%). The live Moina were superior to the other foods with a significantly higher weight gain (1708.92±54.03%), length gain (287.70±4.76%) and specific growth rate (9.45±0.1%/d). The higher protein (66.16%) and n-3 HUFA (10.20%) levels in Moina may explain these results.

Inheritance of mercury tolerance in the aquatic oligochaete Tubifex tubifex.

Resistance to contaminants is an important yet unmeasured factor in sediment toxicity tests. The rate at which mercury resistance develops and its genetic persistence in the oligochaete worm Tubifex tubifex were studied under laboratory conditions. Worms were raised for four generations under two different sediment treatments, one reference clean sediment, the other contaminated with mercury. Worms raised in mercury-contaminated sediment developed mercury tolerance that persisted even when the worms were raised for three subsequent generations in clean sediment. Mercury tolerance was determined by comparative water-only toxicity tests with mercury as the only stressor. Control worms had a mean lethal concentration (LC50) of 0.18 mg/L(-1). Worms exposed to high levels of mercury in sediment had high mercury tolerance with a mean LC50 of 1.40 mg/L(-1). When mercury-tolerant and control mercury-intolerant worms were crossed, their descendants also demonstrated mercury tolerance during lethal toxicity tests. The LC50 for worm descendants resulting from this cross was 1.39 mg/L(-1). Adaptation to mercury exposures occurred rapidly in this group of worms and appears to be due to both phenotypic and genotypic mechanisms. Development of contaminant resistance and adaptation may be common phenomena in aquatic benthic invertebrates, which should be considered during the design and interpretation of toxicity tests.

The Toxicity of Bayluscide and TFM to Tubifex tubifex: Implications for Chemical Control of the Oligochaete Host of Myxobolus cerebralis, the Causative Agent of Whirling Disease

AbstractStandard 24‐h toxicity tests were performed to determine the acute toxicity of Bayluscide (5,2′‐dichloro‐4′‐nitrosalicylanilide) and 3‐trifluoromethyl‐4‐nitrophenol (TFM) to two strains of the oligochaete worm Tubifex tubifex exposed and unexposed to Myxobolus cerebralis, the causative agent of whirling disease. In addition, microcosm trials were conducted to test the effect of three treatment levels of each chemical on the density of T. tubifex in an earthen hatchery pond. In the toxicity tests, worms that were susceptible to M. cerebralis infection were more sensitive to both chemicals than worms that were resistant to the parasite. The toxicity differences of exposed and unexposed worms within a lineage were not as great as those between lineages. Among worms that were susceptible to M. cerebralis, the concentrations of TFM that were lethal to 50% of the test organisms (LC50s) were 6.3 mg/L for worms that had been exposed to M. cerebralis myxospores and 7.3 mg/L for unexposed worms; for resistant worms, the corresponding LC50s were 8.2 and 7.7 mg/L. Among susceptible worms, the LC50s of Bayluscide were 0.060 mg/L for organisms exposed to M. cerebralis myxospores and 0.062 mg/L for unexposed organisms; resistant worms had LC50s of 0.096 and 0.106 mg/L. In the microcosm trials, Bayluscide treatments reduced worm densities by 73–82%, while the TFM treatments reduced worm densities by 34–88%. Given its rapid degradation, relatively selective toxicity, lower cost, and regulatory status, Bayluscide appears to be the best candidate for further study as a chemical control of the oligochaete host of the parasite that causes whirling disease in salmonid fishes.

Effects of the interaction between tubificid worms on the functioning of hyporheic sediments: an experimental study in sediment columns

The main objective of this study was to quantify the importance of interactions between two genera of tubificid worms (Limnodrilus and Tubifex) on processes occurring in hyporheic sediments. The importance of interaction between tubificid worms was estimated by comparing, at a same density of 100 worms, the influence of individual genera with the combination of the two genera. We measured the effect of worms on sediment redistribution, dissolved oxygen consumption and microbial distribution within low filtration gravel-sand columns. The results showed that 100 Limnodrilus, 100 Tubifex, and the combination of the two genera (50 Limnodrilus and 50 Tubifex) all stimulated the O 2 consumption and bacterial numbers in the upper layer of sediment (from 5 cm above to 5 cm below the sediment surface). However, the combination of the two genera produced higher sediment redistribution and a higher stimulation of the number of bacteria in the top 5 cm of the sediment than Limnodrilus and Tubifex tested separately at the same density. Furthermore, the combination of the two genera produced lower oxygen consumption than the two genera tested separately in the deep layers of the sediment. Thus, the interactions within the group of tubificids played a significant role in the functioning of the first cm of the sediments and should not be neglected when assessing their roles in subsurface ecosystems.

Effects of water temperature and substrate type on spore production and release in eastern Tubifex tubifex worms infected with Myxobolus cerebralis.

Eastern Tubifex tubifex worms were exposed to Myxobolus cerebralis spores at 9, 13, 17, and 20 C in 1-L jars that contained sand, mud, or leaf litter as substrata. Beginning 60 days after exposure, water from each jar was filtered daily and examined for the presence of waterborne triactinomyxon spores (TAMs). On discovering a single TAM from an experimental jar, 48 T. tubifex worms from that jar were placed individually into 24-well plates. Spores released from individual infected T. tubifex worms were quantified to determine the first day of TAM release from infected worms, the infection rate, the total number of TAMs released per worm, and the duration of release. No TAMs were found in any of the jars incubated at 20 C or in uninfected, control worms at any temperature. The total number of TAMs released by infected worms in mud and sand was highest at 13 C compared with other temperatures. Infection rates among individual worms increased with temperature between 9 and 17 C. Higher temperatures (up to 17 C) induced earlier TAM releases among infected worms, and substratum did not influence this production parameter. The average duration of TAM release decreased as the temperature increased from 9 to 17 C, and there was a significant effect of substratum in the groups maintained at 13 and 17 C. In all temperature treatments between 9 and 17 C, the duration of release was least in the worms maintained in leaf litter, as was the total number of TAMs released during the experimental period and the median number of TAMs per production day.