Control Aquaria Research Articles

The Impact of Long-Term (4 Months) Exposure to Low pH and Elevated Temperature on the Growth Rate of Gold Mollies’ (Poecilia Sphenops) Larvae

Researchers in the marine ecosystem have documented the significant impacts that anthropogenic ocean acidification has on marine organisms. These include olfactory abilities in fish, impaired behavioral as well as physiological changes, including anti-predatory response leading to consequences in population dynamics and community structure. In this research, we endeavored to investigate and compare the growth rate of the gold mollies (Poecialia sphenops) larvae under a low pH of 5 water temperature of 28 O C, and a pH of 6.9 at a water temperature of 26 O conditions. The mollies larvae were weighed for four months (August, September, October, and November) and the data collected was analyzed using the Statistical Package for Social Sciences (IBM SPSS). The analysis was a multivariate test for a more complete examination of data by looking at independent variables and their relationship to one another. There was no statistically significant difference in the growth rate in August (p-value 0.969) and September (p-value 0.286) between the larvae in aquarium A (experimental) and those in aquarium D (control) at the beginning of the experiment. But there was a statistically significant difference in the third (3) month (October) P-value = 0.007 and in the fourth month (4) (November) P-value = 0.004. The low pH of 5 impacted the growth rate of the Poecilia sphenops larvae while those in the control aquarium pH of 6.9 seemed to have not been affected and grew well.

Use of minute duckweed (Lemna perpusilla) for supplemental feed in catfish (Clarias sp.) culture: determination of the optimal proportion using powersim simulation

Catfish farming is very profitable because the fish is easy to rear and can be harvested quickly. However, the cost of feed as the most significant component in production costs is currently getting higher. The availability and utilization of alternative feed is an urgent solution in creating sustainable catfish farming. This research was carried out during December 2020 – January 2021 in the Research Center for Limnology, Cibinong, Indonesia, which aims to determine the optimal proportion of minute duckweed (Lemna perpusilla) biomass added as feed supplemental to obtain an optimum growth of catfish fingerlings (Clarias sp.). Catfish were reared for 63 days in nine aquariums with a density of 25 fish per aquarium. The commercial pellet given in the control aquarium was 100% pellet portion (5% of the total fish weight), while in the treatment aquariums were 60% and 40% of the total fish weight. As compensation, fresh duckweed (L. perpusilla) was provided ad libitum. Fish were sampled twice to measure their weight and body length. This study showed that the proportion of duckweed as much as 40% as a supplement for commercial pellets could produce optimal catfish growth.

Assessment of antioxidant system, cholinesterase activity and histopathology in Lithobates catesbeianus tadpoles exposed to water from an urban stream

Anthropogenic activities promote changes in community structure and decrease the species abundance of amphibians. The aim of this study was to assess potential alterations in the antioxidant system and cholinesterase activity, histopathological and oxidative damage in Lithobates catesbeianus tadpoles exposed to water from the Cascavel River, in Southern Brazil. Water samples (140 L each) were collected from the headwater, urban and rural areas of the river. Tadpoles were acclimated for seven days. After acclimatization tadpoles were reared in water from the river, except for the control aquarium. After seven days, a portion of the liver was removed and prepared for cholinesterase (ChE), superoxide dismutase (SOD), catalase (CAT) and lipid peroxidation (LPO) analysis; another part of the tissue was prepared for histological examination. An elevation of CAT activity was observed for water from both urban and rural environments. A decrease in LPO reaction was detected, mainly among the tadpoles exposed to water from the rural area. These alternations can cause delay the metamorphosis and lead to metabolic dysfunction, interfering in survival capacity and diminishing, not only individual fitness, but that of the whole population.

Increasing salinity drastically reduces hatching success of crustaceans from depression wetlands of the semi-arid Eastern Cape Karoo region, South Africa

Salinity is an important factor affecting freshwater aquatic species distribution and diversity. The semi-arid Eastern Cape Karoo region of South Africa has been earmarked for shale gas development through hydraulic fracturing. The process uses large amounts of water and produces briny wastewater. When not managed properly, these wastewaters may lead to salinisation of surface freshwater bodies in the region. Therefore, the effect of salinity on the hatching success of crustacean resting eggs was examined using sediments from four depression wetlands found in the region. The sediments were exposed for 28 days to salinity levels of 0.5 g L−1, 2.5 g L−1, 5 g L−1 and 10 g L−1. Control aquaria in which no salt was added were also set up. There was a significant decrease in the emerged taxa richness and abundances at salinities of 2.5 g L−1 and above. Anostraca, Notostraca and Spinicaudata hatchlings were abundant at salinities of 0.5 g L−1 and below, while Copepoda, Daphniidae (Cladocera) and Ostracoda were observed in the highest salinity, but their densities were still lower with increased salinities. Given the importance of large branchiopods in the trophic balance of depression wetlands, their loss may alter the ecological balance and function of these ecosystems.

Effects of chemotherapeutics against experimentally injured stinging catfish Heteropneustes fossilis

Effects of different chemotherapeutics were examined against experimentally infected stinging catfish Heteropneustes fossilis. Fish were collected from a fish market in Mymensingh, acclimatized for 7 days in laboratory condition from January to February, 2016 in aquaria at Fish Clinic of Bangladesh Agricultural University, Mymensingh, experimentally injured by using forceps and knife and waited seven days for the establishment of infection. Before starting chemotherapeutic trial, it was confirmed that the fish were infected with microorganisms by clinical diagnosis in laboratory condition. They showed hemorrhages and ulcerative lesions over the infected area. A total of 80 such experimentally infected stinging catfish having average body weight of 18 g were used for the experiment. Two chemotherapeutics: antibiotic, Eryvet (erythromycin thiocyanate INN, sulphadiazine (NaUSP) & trimithoprim BP) and antifungal, methylene blue were used in separate and combined treatment with three different doses of antibiotic. The same dose of methylene blue, 0.2 mg/l, was used for separate and combined treatment by antibiotic. Doses of antibiotic (Eryvet) were 0.8 g/10 kg body weight of fish, 1g/10 kg body weight of fish and 1.2 g/10 kg body weight of fish as lower dose, recommended dose and higher dose respectively. For combined treatment the above different doses of antibiotic and the same dose of antifungal were used. Water was exchanged regularly. The chemotherapeutic trial was conducted for 7 days and observation was continued for another 8 days to observe the effect of treatment. Combined treatment with the recommended dose of the antibiotic and methylene blue showed the best result where 90% fish were recovered. By the treatment with the higher dose of the antibiotic 70% fish were recovered. Antifungal treatment showed that 20% fish were recovered. All the fish in negative control aquarium died.Asian J. Med. Biol. Res. December 2017, 3(4): 476-487

Toxicity of aqueous extract of white hoary pea, Tephrosia candida (Papilionoideae) on Nile tilapia, Oreochromis niloticus (Cichlidae) fingerlings

Fish poisoning using Tephrosia candida , which is an exotic plant to Sri Lanka is taking place in streams in the boundary of the Sinharaja forest, a tropical forest range, designated as a world heritage site by UNESCO in 1988. T. candida is a source of flavonoids and rotenoids including rotenone, tephrosin, and deguelin. Fishermen add large amounts of grounded plant matter to kill almost all the fishes in the stream within a short period of time. This method of unregulated fishing may have a long term negative effect on fish diversity and abundance in the area. A 96 h static renewal toxicity bioassay was carried out in the laboratory to determine the median lethal concentration (LC 50 ) of aqueous extract of T. candida leaves on Oreochromis niloticus fingerlings. Experimental fish were exposed to test water in 20 L glass aquaria with concentrations of plant extract of 5, 7.5, 10, 15 and 20 mg L -1 . All five treatments aquaria and the control aquaria without plant extract were triplicated. Fish exposed to plant extract showed symptoms of toxicity including, initial inactivation, agitated swimming, turning movement, air gulping, increased opercular movement followed by erratic swimming, loss of reflex, slow opercular movement, setting at the bottom motionless and knockdown before death. The gills of the dead fishes were damaged, swollen and external bleeding were observed. Lower concentrations of the extracts had sub lethal effects which manifested as zigzag movement, air gulping, increased opercular movement and some fish gathered near the air stones. The LC 50 values at various exposure periods were 10.83 mg L -1 for 24 h; 8.61 mg L -1 for 48 h; 7.26 mg L -1 for 72 h and 6.43 mg L -1 for 96 h. It could be concluded that the application of T. candida extract causes lethal toxic effects on fish even at very low concentrations.

Effectiveness of oxytetracycline in reducing the bacterial load in rohu fish (Labeo rohita, Hamilton) under laboratory culture condition

Objective: To observe the effectiveness of most widely used antibiotic, oxytetracycline (OTC) in reducing the bacterial load in rohu fish under artificial culture condition in the laboratory. Methods: The experiment was conducted in the Faculty Fisheries, Bangladesh Agricultural University, Mymensingh-2202. The fish were reared in 8 aquaria where fish in 5 aquaria were used for replication of the treatment (experimental group) and fish in remaining 3 aquaria were considered as a control (Control group). OTC was fed to the fish in the experimental aquarium at the rate of 2 g/kg through diet twice daily whereas fish reared under control condition was given feed without antibiotic for 20 d and bacterial content in the aquarium water, gills, skin and intestine of fish were estimated at every alternative day after onset of the experiment. Results: Rearing the fish with OTC treated feed resulted in gradual decrease of bacterial load in the aquarium water, gills, intestine and skin of the fish whereas the content remain unchanged or little increased in the control group. Water quality parameters such as dissolved oxygen, pH and total hardness were within the suitable range in the experimental aquarium but not in control aquaria throughout the experimental period. Conclusions: These results suggest that OTC could be a potential antibiotic to reduce the bacterial load in fish and can be used commercially for maintaining the fish health in aquarium conditions.

Combined Application of Ferrihydrite-Modified Diatomite and Gypsum to Phosphorus Control in a Laboratory-Scale Artificial Aquarium

Effects of the combined application of ferrihydrite-modified diatomite (FHMD) and gypsum on phosphorus control were investigated in a laboratory-scale artificial aquarium under anoxic and agitation conditions over 120 days. Daily oscillation of a metal grid to simulate agitating effects by wind did not yield the sediment resuspension in the 120-day treatment aquarium (120-day aquarium) due to the gypsum stabilization, while significant sediment resuspension was observed in the control aquarium. The combined application of FHMD and gypsum did not affect the total kjeldahl nitrogen (TKN) concentrations in both the control aquarium and the 120-day aquarium. Under anoxic conditions and sediment resuspension conditions, a large increase in total phosphorus (TP) concentrations was observed in the control aquarium. However, the TP concentrations in the 120-day aquarium stayed relatively stable, within a range of 9.1–13.3 μg/L. After the 120 days’ incubation, translocation from mobile labile-P and organic-P to P adsorbed by FHMD occurred. The combined application of FHMD and gypsum effectively maintained TP levels within the oligotrophic range under anoxic and agitation conditions in the laboratory-scale artificial aquarium by removing phosphorus from lake water and reducing sedimentary phosphorus release via gypsum sediment stabilization and FHMD phosphorus immobilization.

Predation by green crab and sand shrimp on settling and recently settled American lobster postlarvae

Very little is known about predation on early life stages of the American lobster, Homarus americanus Milne Edwards, 1837, including the identity of predators and the threat they represent. In this laboratory experiment, we investigated the predatory threat that green crabs, Carcinus maenas (Linnaeus, 1758), and sand shrimp, Crangon septemspinosa Say, 1818, represent to settling and recently-settled lobster postlarvae. Lobster survival within 48 hours varied between 80-100% in control aquaria. In contrast, survival was only 40-60% in the presence of sand shrimp and 0-20% in the presence of green crab. Some sand shrimp were observed successfully catching and preying upon lobster as they were exploring the substrate for settlement, whereas green crab seem to have captured lobsters after they had adopted a benthic mode of existence. Since both of these predators commonly inhabit shallow cobble-bottom habitat where lobster settlement occurs, they could be important predators of young lobsters. Given these findings, we believe that future research should undertake the challenging task of confirming predation by green crab and sand shrimp on young lobsters in nature, and we suggest that molecular analysis of predator gut contents is the most promising approach to this question.

Effects of settlement cues on behaviour and substrate attachment of hatchery reared winged pearl oyster (Pteria penguin) larvae

Successful hatchery production of commercial bivalve species requires optimal recruitment of larvae to substrates. This study used two experiments to investigate the effects on recruitment of Pteria penguin pediveliger larvae of (1) treating the culture medium with alternate concentrations of three chemical compounds both in the presence/absence of a bio-film and (2) exposure to five substrate types both in the presence/absence of a chemical cue. Small 10mL aquaria were stocked with 1larvaemL−1 and given a 25×25mm piece of horizontally-oriented flat substrate. The proportion of larvae within each treatment that displayed various behaviours (swimming/sitting/crawling), had settled using byssal attachment or had undergone mortality was recorded at 24, 48 and 72h. After 48h, settlement of P. penguin was 65% greater in aquaria containing a substrate covered by a naturally formed bio-film than in control aquaria. The neuroactive compounds 5-hydroxytryptamine (serotonin) and γ-aminobutyric acid (GABA) and the chemical compound potassium chloride (KCl) all acted to decrease larval swimming behaviour when compared to controls with untreated seawater. Exposure to KCl (20mM) also resulted in more larvae crawling over the substrate surface. After 72h, settlement of larvae in aquaria treated with serotonin (10−3M) or KCl (20mM) was significantly greater than in control aquaria by 75% and 84%, respectively, while exposure to GABA had no effect. The positive effect of a bio-film on settlement did not change significantly according to chemical treatment of the culture medium, suggesting that the techniques can be used in conjunction. Settlement in response to 20mM KCl was enhanced by the presence of a red nylon mesh substrate with 5mm between filaments. Roughly three times more larvae settled onto this substrate during the first 24h when compared to the same material with a smaller mesh size, black fibreglass screen and smooth plastic substrates. Comparisons with settlement behaviour of other bivalves and the commercial implications of this research are discussed.

The Effects of Egg Stocking Density and Antibiotic Treatment on Survival and Development of Winged Pearl Oyster (Pteria Penguin, Röding 1798) Embryos

Pteria penguin is an important commercial bivalve species that is used in the production of half pearls known as mabè. Expansion of this industry in places with low natural spatfall is reliant on hatchery production of juvenile oysters, which begins with the incubation of fertilized eggs. This study addresses the issue of mortality during egg incubation by examining the effects of egg stocking density and the application of antibiotics. A factorial experimental design was implemented combining 3 egg densities (10, 50, and 100/mL) and 3 antibiotic treatments (control, no antibiotic; 5 mg/mL streptomycin—sulfate; 5 mg/mL tetracycline—erythromycin 2.5:2.5 mg/mL). Antibiotics were added to the culture medium as a single dose and fertilized eggs were incubated for an industry standard period of 24 h. Despite a 23% increase in mean survival during incubation, aquaria treated with tetracycline—erythromycin (1:1) yielded an average of only 9% more veliger larvae than control aquaria as a result of interference with development during the transition of trochophore to shelled larvae (D-stage). Application of the antibiotic streptomycin—sulfate improved mean survival by 16% compared with control aquaria, without significantly compromising development. A high egg density of 100/mL did not significantly reduce survival, but resulted in a 5% reduction in normal development to D-stage. The results of this study show that if tank space is limited during egg incubation, utilizing a high stocking density of 100 eggs/mL will provide the greatest number of D-stage larvae. However, if the supply of eggs is limited, we recommend stocking P. penguin eggs at a density ≤50/mL and minimizing mortality by treating the culture medium with the antibiotic streptomycin—sulfate.

Effect of Organic Fertilizers on Zooplankton Production

Comparative study of zooplankton production, using poultry droppings, pig dung and cow dung was carried out for five weeks using seven glass aquaria (60×30×36) cm³. The aquaria were thoroughly washed, filled with 20litres of bore-hole water, fertilized with the respective organic manures after 4 days fermentation and inoculated with zooplankton samples collected from an earthen fish pond. The highest mean zooplankton population was recorded in the aquarium tanks fertilized with poultry droppings (3989cells/L), followed by pig dung (2783cells/L) cow dung (2030cells/L) and lastly the control aquarium (1140cells/L). Poultry droppings culture had the highest population peak in the second week (8175), pig and cow dung in the third week (5650,4225) and the control in the fourth week (2350). Poultry droppings is therefore recommended for quick and high production of zooplankton which invariably reduces the high cost of imported expensive pelleted feed for fish fry.KEY WORDS: Organic fertilizers, Zooplankton, Production.

Noninvasive assessment of nitrate-induced stress in koi Cyprinus carpio L. by faecal cortisol measurement

This study determined effects of nitrate (NO3−)-induced stress on faecal cortisol levels in koi (Cyprinus carpio). NO3− was presented in two formats: (1) bulk increase followed by dilution to assess cortisol response and recovery and (2) bulk increase followed by incremental increases to assess cortisol response limit. Fish were maintained group-wise in treatment and control aquaria (n=6 per group), and 0.5 g L−1 NO3− (as NaNO3) was added to the water. Faecal samples were collected daily and blood samples were taken pretreatment and 72-h posttreatment and were assayed for cortisol via ELISA. NO3− increased plasma and faecal cortisol 4.4-fold and 3.9-fold respectively. Plasma cortisol was not measured further. After a 74% NO3− decrease by dilution, faecal cortisol decreased to baseline within 24 h, and restimulation by NO3− (1.0 g L−1) elevated faecal cortisol to maximal study levels. In a separate experiment, exposure to 0.4 g L−1 NO3− increased faecal cortisol 6.9-fold. However, three additional 0.4 g L−1 NO3− increments across 9 days did not further increase cortisol. This study demonstrates that faecal cortisol measurement in fish via an ELISA can be useful as an indicator of NO3−-induced stress in the aquatic environment.

Effect of phosalone on haematological indices in the tilapia, Oreochromis mossambicus

The aim of this study was to assess the effect of phosalone on the tilapia, Oreochromis mossambicus. The effect was assessed on the basis of the results of acute toxicity tests and comparison of results of haematological examination of a control and an experimental group exposed to phosalone. The 96 h LC_{50} is the basic value in the acute toxicity test and it was 0.26 mg/L for phosalone against the test fish. Haematological profile of the healthy fish was carried out with 2 sublethal concentrations, viz 0.0325 mg/L (1/8) and 0.065 mg/L (1/4) of phosalone. The experiment was performed semi-statically with a group of 10 fish in 10 experimental aquaria, 2 control aquaria, and 4 aquaria each with different concentrations. The results showed that phosalone had some effect on the haematological parameters of tilapia. It was determined that the total RBCs, WBCs, haemoglobin content, and haematocrit value significantly decreased (P < 0.001). The percentages of erythrocyte sedimentation rate, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration showed an increasing trend with respect to the increase in exposure period in both sublethal concentrations. ANOVA showed that the pesticide concentrations had more influence than the duration of exposure in all cases (P < 0.001).

The effects of elevated ultraviolet B radiation and elevated water temperature on the loss of zooxanthellae from Aiptasia pallida

What effects will elevated ultraviolet B radiation and/or elevated temperature have on the loss of zooxanthellae from Aiptasia pallida? The hypothesis of this study was: if Aiptasia pallida are exposed to elevated ultraviolet radiation and/or elevated water temperatures, then the number of zooxanthellae expelled from the Aiptasia pallida will increase. Sea anemones (Aiptasia pallida) containing symbiotic zooxanthellae (Symbiodinium bermudense) were maintained in 3 L salt-water aquariums on a 10:14 hour light:dark cycle. In addition to a control aquarium, one aquarium was exposed to elevated water temperature, another aquarium was exposed to elevated UVB radiation, and the fourth aquarium was exposed to elevated levels of both UVB radiation and water temperature. The number of zooxanthellae expelled from the sea anemones was measured with a hemacytometer once every three days over a fifteen-day period. The number of zooxanthellae expelled per sea anemone was lowest in the control aquarium. The number of zooxanthellae expelled per sea anemone was greatest in the aquarium that was exposed to elevated levels of both UVB radiation and water temperature. Aquariums that were exposed to elevated levels of either UVB radiation or water temperature experienced moderate levels of expulsion. In conclusion, elevated levels of both UVB radiation and water temperature had a greater effect on the loss of symbiotic zooxanthellae than the effect of either variable individually or the control.

Morphological abnormalities in Chironomus tentans exposed to cadmium—and copper-spiked sediments

The induction of mouthpart deformities and the developmental response with exposure to sediments spiked with three concentrations (9, 39, and 61 μg g −1 Cd dry wt.) of cadmium (Cd) and three concentrations (30, 125, and 215 μg g −1 Cu dry wt.) of copper (Cu) were investigated. Mouthpart deformity proportions in Chironomus tentans larvae were compared between metal-spiked and control populations and between parent and offspring (F1) populations. Cd- and Cu-treated sediments induced deformities (low Cd=13%, medium Cd=7%, high Cd=4%, low Cu=6%, medium Cu=9%, high Cu=6%) at significantly higher proportions than control (3%) sediments. No negative developmental response was determined. Larval sizes in metal-treated aquaria and control aquaria were not significantly different. F1 larvae from parents reared in medium and high Cu had significantly lower deformity rates than their parents. Our research adds to the growing evidence implicating heavy metals in general, and Cd and Cu specifically, as teratogenic agents.

Relationship between exposure duration, tissue residues, growth, and mortality in rainbow trout ( Oncorhynchus mykiss) juveniles sub-chronically exposed to copper

We conducted a 56-day sub-chronic test on the effects of Cu on rainbow trout ( Oncorhynchus mykiss) fry at a nominal water hardness of 100 mg l −1 (as CaCO 3). Response measures were growth, whole body Cu concentrations, and mortality. Significant mortality was observed in fish exposed to 54.1 μg Cu l −1 (47.8%) and 35.7 μg Cu l −1 (11.7%). Growth was dose-dependent over the range of Cu treatments (0–54 μg Cu l −1), and was modeled as a function of Cu exposure concentration and exposure duration. Calculated inhibition concentrations (based on change in wet weight through a 56-day Cu exposure) were IC 50=54.0 μg Cu l −1, IC 20=21.6 μg Cu l −1, IC 10=10.8 μg Cu l −1, and IC 01=1.1 μg Cu l −1. Measured whole body Cu was also dose-dependent, and growth of trout fry was readily modeled as a function of tissue Cu and exposure duration. This model was virtually identical to a model previously developed for rainbow trout exposed to Cu at a hardness of 25 mg l −1. Following the 56-day exposure period, we performed a 96-h acute challenge to Cu and Cd to evaluate the effects of Cu acclimation on acute Cu and Cd toxicity. Sensitivity to Cu was dependent on the ‘acclimation dose’; trout previously held in control aquaria (i.e. not acclimated to Cu) suffered over 80% mortality, whereas trout previously exposed to 35.7 μg Cu l −1 for 56 day suffered 20% mortality. These fish also showed somewhat reduced sensitivity to Cd, suggesting acclimation to Cu can enhance tolerance to other metals. Finally, the relationship between growth response and hardness (derived from several studies) appeared to have a different slope than the hardness relationship previously observed for lethality responses.

The effect of artificial dehydration on the survival and reproduction of Lymnaea rubiginosa

The effect of artificial dehydration on snail Lymnaea rubiginosa was investigated in the laboratory by monitoring its survival and development, because as aquatic organism, this snail must be able to adapt or tolerate with the changes in its habitat. Fifty laboratory-reared L. rubiginosa with shell length between 1.0-1.5 cm (adult) were placed in each sloping earth aquarium (60x80x20 cm) which were already filled with water about 15 cm depth. Five aquaria were used in this study, and one week after being established the water from 4 aquaria was drained while one aquarium was retained with water as a control. The water was replaced in one of dehydrated aquarium each week for four weeks, commencing one week after draining the water. The survival of snails in each aquarium were recorded every two days over a period of 3 months. The results indicated that the mortality rate of adult snails increased as the period of dehydration increased. After four week dehydration only 16% of adult snails survive compared to 68% survival in the control aquarium, and dehydration for 4 weeks prolonged the hatching time of eggs. Moreover, in dehydrated aquaria, the egg masses were deposited in a random pattern on the surface of the soil, whereas in the control aquarium they were laid on the soil-water junction. Key words : Dehydration, Lymnaea rubiginosa , survival, fasciolosis

ADAPTIVE PLASTICITY IN AMPHIBIAN METAMORPHOSIS: RESPONSE OFSCAPHIOPUS HAMMONDIITADPOLES TO HABITAT DESICCATION

Amphibians exhibit extreme plasticity in the timing of metamorphosis, and several species have been shown to respond to water availability, accelerating metamorphosis when their ponds dry. In this study we analyzed the plasticity of the developmental response to water volume reduction in the western spadefoot toad, Scaphiopus hammondii. Also, we attempted to identify the environmental cue(s) that may signal a desiccating larval habitat. We spawned adults in the laboratory and raised tadpoles in aquaria in a controlled environmental chamber. Water levels of aquaria were gradually reduced by removing water at the rate of 0.5–1 L/d; water in control aquaria was similarly disturbed but not removed. Tadpoles subjected to water volume reduction showed significant acceleration of metamorphosis. The developmental acceleration depended on the rate of reduction of the water level; i.e., tadpoles exhibited a continuum of response. This developmental response did not result from thermal differences between treatments...

Chironomid larval deformity frequencies, mortality, and diversity in heavy-metal contaminated sediments of a Canadian riverine wetland

Sediment sampling at point source locations in the Niagara River watershed revealed an area in a Class One Provincially Significant Riverine Wetland that was located near the discharge of a stainless steel company. The site had unusually high concentrations of heavy metals and oily wastes in its sediments. The impacts of these oil and heavy metal contaminated sediments on an invertebrate population of midge (chironomid) larvae was assessed using both lab and field techniques. The midge larvae were the dominant invertebrates in this section of the river. Twenty-six percent of the chironomids from sites located 10 to 800 m downstream of the stainless steel company's point source were deformed. A lab study was carried out to determine what percentage of the observed deformities could be attributed to the heavy metal content of the sediments and what percentage was due to the organic fraction. Sediments collected near the point source were tested and found to be acutely toxic. Sediments collected 60 m downstream of the point source were teratogenic. The frequency of mentum deformities for chironomids reared in clean sediments (control aquaria) was only 2.2%. A similar deformity frequency (2.2%) was observed at the clean sediment reference site in the Welland River watershed. Of the 97 chironomids removed from the de-oiled heavy metal contaminated sediments in the test aquarium, 10.3% displayed deformities. This is believed to be one of the few times that chironomid deformities were induced in a controlled lab study in which heavy metal concentrations similar to those found in the field were used.