Freshwater Shrimp Caridina Nilotica Research Articles

Biomarker Responses in the Freshwater Shrimp Caridina nilotica as Indicators of Persistent Pollutant Exposure.

Biomarkers are applied as early warning indicators of organisms' exposure to pollutants. The aim of this study was to utilise a multi-biomarker approach in the freshwater shrimp Caridina nilotica (Decapoda: Atyidae) as indicators of persistent pollutant exposure. A suite of biomarkers was selected to cover oxidative stress and damage, and energetics of the organisms. Five sites, representing an agricultural and pesticide application gradient, were sampled during two flow related hydro-periods in rivers of the Phongolo floodplain, north-eastern South Africa. Cytochrome P450 (CYP) activity was significantly higher in shrimp at sites directly adjacent to regions of increased human activity. Increased oxidative responses, i.e. catalase (CAT; p < 0.01) and protein carbonyl (PC, p < 0.01) were also found at these sites. The energetics biomarker did not show any influence of increased contaminant exposure. We demonstrated that the biomarkers of exposure (CYP) and effect (CAT, PC) were suitable to detect effects of stressors, probably persistent pollutants.

Acetylcholinesterase activity in the freshwater shrimp Caridina nilotica as a biomarker of Roundup® herbicide pollution of freshwater systems in South Africa

The use of Caridina nilotica whole-body acetylcholinesterase (AChE) activity as a potential biomarker of Roundup(®) pollution of aquatic ecosystems was investigated. Forty days post hatch (dph) shrimps were exposed to different concentrations of 0.0, 4.3, 6.7, 10.5, 16.4, 25.6 and 40.0 mg/L in a 96 h acute toxicity test; and 0.0, 2.2, 2.8, 3.4, 4.3 and 5.4 mg/L in a 21 d chronic toxicity test. Whole-body AChE activities were determined at the end of the exposure periods by spectrophotometric assay of sample extract; activities were then normalized against protein contents in the samples and expressed in nanomoles of substrate hydrolyzed. Results of both tests showed that AChE activity was concentration-dependent. Mean AChE activities and standard deviations (±SD) for 96 h acute toxicity were 3.6239 (± 0.4185), 3.4157 (± 1.1842), 2.537 (± 1.3989), 2.4253 (± 1.4202), 2.4127 (± 1.9097), 2.0017 (± 1.1080) and 2.316 (± 0.4001) nmol/min/mg protein; while activity levels for 21 d test were 3.6907(± 0.3401), 2.8473 (± 0.713), 2.9134 (± 0.9879), 2.6738 (± 0.7117), 2.3019 (± 0.4464) and 2.1478 (± 0.864) nmol/min/mg protein. Reference basal AChE activity for 40 dph C. nilotica based on the two control groups was estimated as 3.6907 (± 0.3401) nmol/min/mg proteins. The present work provides ecotoxicological basis for the possible use of AChE activity in C. nilotica as a biomarker for monitoring Roundup(®) pollution in freshwater systems.

Lipid peroxidation in the freshwater shrimp Caridina nilotica as a biomarker of Roundup® herbicide pollution of freshwater systems in South Africa

Glyphosate-based herbicides used to control weeds and invading alien plant species in South Africa ultimately end up in freshwater ecosystems, but no South African environmental water quality guideline exists to regulate these bio-active chemicals. Ecotoxicological tests to assess the possibility of using lipid peroxidation (LPx) in Caridina nilotica as a potential biomarker of Roundup(®), a glyphosate-based herbicide, pollution were conducted. In two separate tests, 40 days post hatch shrimps were exposed to different concentrations of 4.3, 6.7, 10.5, 16.4, 25.6 and 40.0 mg/L in a 96 h acute toxicity test; and 2.2, 2.8, 3.4, 4.3 and 5.4 mg/L in a 21 d chronic toxicity test, using static-non renewal and static-renewal methods, respectively. Shrimp whole body LPx was estimated by thiobarbituric acid reactive species (TBARS) assay, performed by a malondialdehyde (MDA) reaction with 2-thiobarbituric acid (TBA) measured spectrophotometrically. Final MDA concentrations were expressed as nmol MDA produced/mg protein. Results showed that LPx was significantly lower in control animals than in animals exposed to different Roundup(®) concentrations, (p < 0.05). The present work provides an ecotoxicological basis for the possible use of LPx in Caridina nilotica as a biomarker for monitoring Roundup(®) pollution in freshwater ecosystems.

Using growth measures in the freshwater shrimp Caridina nilotica as biomarkers of Roundup® pollution of South African freshwater systems

There has been global concern about the effect of toxic chemicals on aquatic biota due to the upsurge in contamination of aquatic ecosystems by these chemicals, which includes pesticides. Roundup® and other glyphosate-based herbicides are frequently used in the chemical control of weeds and invading alien plant species in South Africa. These bio-active chemicals ultimately get into water courses directly or indirectly through processes such as drifting, leaching, surface runoff and foliar spray of aquatic nuisance plants. However, there is no South African water quality guideline to protect indigenous freshwater non-target organisms from the toxic effects of glyphosate-based herbicides. This study evaluated the possible use of growth measures in Caridina nilotica as biomarkers of Roundup® pollution as part of developing glyphosate water quality guideline for the protection of aquatic life in South Africa. Using static-renewal methods in a 25-day growth toxicity test, 40days post hatch shrimps were exposed to different sub-lethal Roundup® concentrations of 0.0 (control), 2.2, 2.8, 3.4, 4.3 and 5.4mg/L. Shrimps were fed daily with TetraMin® flake food and test solutions changed every third day. Shrimp total lengths and wet weights were measured every fifth day. These data were used to determine the shrimp’s growth performance and feed utilization in terms of percent weight gain (PWG), percent length gain (PLG), specific growth rate (SGR), condition factor (CF), feed intake (FI), feed conversion ratio (FCR) and feed conversion efficiency (FCE). Moulting was observed for 14days and the data used to determine the daily moult rate for each concentration. Results of growth performance and food utilization indices showed that growth was significantly impaired in all exposed groups compared to control (p<0.05). Moulting frequency was also higher in all exposed groups than in control (p<0.05). Although all the tested growth measures proved to be possible biomarkers of Roundup® pollution, moulting frequency gives a clearer indication of the sub-lethal effects of Roundup® toxicity.

Acute toxicity of Roundup® herbicide to three life stages of the freshwater shrimp Caridina nilotica (Decapoda: Atyidae)

Glyphosate based herbicides, including Roundup®, are frequently used in the chemical control of weeds and invading alien plant species in South Africa. These herbicides ultimately get into water courses directly or indirectly through processes such as drifting, leaching, surface runoff and foliar spray of aquatic nuisance plants. Despite their widespread use, no water quality guideline exists to protect indigenous South African freshwater organisms from the toxic effects of these herbicides. The toxicity of the herbicide Roundup® was assessed using three different life stages of the freshwater shrimp Caridina nilotica, a prevalent species in South African freshwater ecosystems. Neonate (<7days post hatching (dph)), juvenile (>7dph and <20dph) and adult (>40dph) shrimps were exposed to varying concentrations (1.5–50mg/L acid equivalence (a.e.)) of the herbicide in 48 and 96h acute toxicity tests in order to determine the most sensitive life-stage. The results showed neonates to be more sensitive to Roundup® than both juveniles and adults with mean 96h LC50 values of 2.5, 7.0 and 25.3mg/L a.e. respectively. The estimated 96h LC50 of neonates is much lower than the application rate (20–30mg/La.e.), although the application’s impact will depend on the dilution rate of the applied concentration in the environment. All three life-stages of unexposed animals exhibited active and coordinated movement but exposed shrimps were erratic and slow in their movements, with neonates showing most of these behavioral irregularities. This study shows that low levels of the herbicide Roundup® may adversely affect C. nilotica health and survival. Thus, the herbicide should be carefully managed to minimize any negative impact on non-target freshwater organisms.

A chronic toxicity test protocol using Caridina nilotica (Decapoda: Atyidae) and the generation of salinity toxicity data

Salinization of freshwater resources is an increasing global problem, yet there is a paucity of chronic salinity tolerance data linked to very few chronic toxicity test protocols. This research aimed to generate a chronic toxicity test protocol and protective salinity tolerance data for the indigenous South African freshwater shrimp Caridina nilotica. In addition, the theory that LC5s (concentration causing 5% lethality) are indicative of No Observed Effect Concentrations (NOECs) was tested. NaCl and Na2SO4 were used as toxicants as they are indicative of natural and industrial salinization, respectively. NOEC values of 1.9 g l–1 were calculated for both salts. Within the chronic toxicity tests, LC5s that were calculated using regression methods approximated the calculated NOEC values for both salts. Chronic NOECs calculated here are lower, by a factor of 3, than the acute LC50s calculated for the same species and salts. Although evidence exists to suggest that C. nilotica is generally sensitive to toxicants, it was found to be not particularly sensitive to salinity. However, the species was found to be a good chronic toxicity test organism for partial life-cycle toxicity tests where growth was measured as the test endpoint, and may yield valuable chronic toxicity data for other toxicants.

Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya

SUMMARY. Seasonal changes in population structure, standing stock levels and production of Caridina nilotica were studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum of c. 1400 to a minimum of c. 350 individuals per m2 (3.4–0.4 g m−2 dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels.Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size‐specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length.Estimates of overall mean annual somatic production (g m−2 year−1 dry wt) for the three sites between January 1975 and January 1976 ranged between c. 132 (egg‐ratio method), 37.5 (summation of growth increments) and 24 (Hynes‐Hamilton method) at an annual mean standing stock level of 2.7 g m−2 dry wt (calorific value, 20.34 kJ g−1 dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m−2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m−2 year−1 dry wt (calorific value, 28.01 kJ g−1) at sites 1, 2 and 3, or 2.7 g m−2 year−1 on average.

Embryonic duration and post‐embryonic growth rates of the tropical freshwater shrimp Caridina nilotica (Decapoda:Atyidae) under laboratory and experimental field conditions

SUMMARY. Embryonic durations and post embryonic growth rates of Caridina nilotica were determined under laboratory conditions at constant temperatures near 18, 24 and 30°C. Embryonic durations and intermoult intervals were negative curvilinear functions of temperature. At a given temperature moulting frequency varied inversely with shrimp size and slight sexual differences were apparent. Moulting frequency of berried females was governed by the temperature‐specific embryonic durations.Growth rates were determined from changes in carapace length (CL) of individual shrimps (laboratory) or batches of shrimps (field enclosures) over 1 month and these data were used to calculate temperature‐specific life‐long growth curves for males and females. Growth in body mass was estimated indirectly from the carapace length‐mass relationship of C. nilotica. On average, males grew marginally faster than females during the first 2 months of life, but growth of males larger than CL= 4 mm was considerably depressed relative to that of females. Inflexions in growth rate, apparently related to the onset of sexual maturity, were apparent in both sexes.Under laboratory conditions, the growth rate of males increased with temperature, but temperature‐related differences were not as marked in females. Notwithstanding the more rapid moulting rate at 30°C the growth rate of females was slightly slower at 30 than at 24°C as a result of marginally but significantly smaller per moult growth increments observed at 30°C in animals up to CL= 5.5 mm. Possible reasons for this depressed growth are discussed.Growth rates of animals in field enclosures in Lake Sibaya over 1 month in winter (20 ± 3°C) were generally comparable to those estimated for the 18°C laboratory experiments. Growth rates in enclosures containing tripled standing stocks were almost identical to those containing the naturally occurring biomass of animals, suggesting a non‐limited environment at least during the time of the experiment.