Daniela Baganz

Impact of the cyanobacteria toxin, microcystin-LR on behaviour of zebrafish, Danio rerio

Abstract Quantitative behaviour of zebrafish, Danio rerio, was recorded to assess and predict long-term sublethal effects of the cyanobacteria toxin microcystin-LR (MCYST-LR; nominal concentrations of 0.5, 5, 15 and 50 μg litre−1) by using the automated BehavioQuant®. The exposure to MCYST-LR caused dose–effect related changes in spontaneous locomotor activity. Whereas the two lower exposure concentrations (0.5 and 5 μg litre−1) caused an increase in daytime motility, elevated exposures led to significantly decreased motilities. The highest exposure (50 μg litre−1) also reduced the spawning activity and success. In contrast to daytime activities, night-time swimming activity was significantly greater at the higher MCYST-LR exposures. The chronobiological analysis indicated a phase shift of maximum swimming activities and a lowered reaction on trigger points like feeding, at dusk and dawn. Furthermore, the results indicate some adverse consequences in reproduction success and in the spatial and temporal fit of the fish into its habitat.

Temporal pattern in swimming activity of two fish species ( Danio rerio and Leucaspius delineatus ) under chemical stress conditions

Circadian periodicity of swimming activity was investigated in two fish species, the zebrafish (Danio rerio) and the sunbleak (Leucaspius delineatus) under sublethal long-term exposure to the cyanobacteria toxin microcystin-LR (nominal concentrations of 0.5 μg l − 1, 5 μg l − 1, 15 μg l − 1, 50 μg l − 1) in 15-litre tanks. Swimming activity of fish was monitored continuously by using an automated video-monitoring and object-tracing system over a period of 17 days. Influenced by long-term exposure to microcystin-LR, Leucaspius delineatus reversed their significant diurnal swimming activity and the fish became statistically significant nocturnal. Danio rerio remained diurnal active, but a significant phase shift was registered. In both Danio rerio and Leucaspius delineatus analysis of time series by cosinor regression revealed microcystin-LR induced dose-dependent alterations of the mean of oscillation, amplitude, acrophase and period length in a different extent. For Danio rerio the periodogram analysis revealed a significant circadian component of swimming activity for control as well as exposure groups, whereby the spectral amplitude clearly decreased at microcystin-LR concentrations of 15 and 50 μg l − 1. For Leucaspius delineatus the amplitude of circadian rhythm was decreased at all exposure concentrations of MC-LR. Furthermore the dominance of circadian rhythm was clearly reduced, whereas the rate of ultradian rhythms increased at elevated MC-LR concentrations of 5 μg l − 1, 15 μg l − 1 and 50 μg l − 1. The studied temporal aspects of behaviour clearly indicated stress symptoms in both fish species, therefore it proved to be a relevant method to characterise the impact of toxic substances in the environment and for biomonitoring.

Model of an aquaponic system for minimised water, energy and nitrogen requirements

Water and nutrient savings can be established by coupling water streams between interacting processes. Wastewater from production processes contains nutrients like nitrogen (N), which can and should be recycled in order to meet future regulatory discharge demands. Optimisation of interacting water systems is a complex task. An effective way of understanding, analysing and optimising such systems is by applying mathematical models. The present modelling work aims at supporting the design of a nearly emission-free aquaculture and hydroponic system (aquaponics), thus contributing to sustainable production and to food security for the 21st century. Based on the model, a system that couples 40 m(3) fish tanks and a hydroponic system of 1,000 m(2) can produce 5 tons of tilapia and 75 tons of tomato yearly. The system requires energy to condense and recover evaporated water, for lighting and heating, adding up to 1.3 GJ/m(2) every year. In the suggested configuration, the fish can provide about 26% of the N required in a plant cycle. A coupling strategy that sends water from the fish to the plants in amounts proportional to the fish feed input, reduces the standard deviation of the NO3(-) level in the fish cycle by 35%.

Efficient and economical way of operating a recirculation aquaculture system in an aquaponics farm

ABSTRACT In this article, optimal control methods based on a metabolite-constrained fish growth model are applied to the operation of fish production in an aquaponic system. The system is formulated for the twin objective of fish growth and plant fertilization to maximize the benefits by optimal and efficient use of resources from aquaculture. The state equations, basically mass balances, required by the optimization algorithms are given in the form of differential equations for the number of fish in the stock, their average weight as mediated through metabolism and appetite, the water recirculation and waste treatment, hydroponic nutrient requirements and their loss functions. Six parameters, that is, water temperature, flow rate, stock density, feed ration size per fish, energy consumption rate and the quality of food (percentage of digestible proteins) are used to control the system under dynamic conditions. The time to harvest is treated as a static decision variable that is repeatedly adjusted to find the profit-maximizing solution. By modeling the complex interactions between the economic and biological systems, it is possible to obtain the most efficient decisions with respect to diet composition, feeding rates, harvesting time and nutrient releases. Some sample numerical results using data from a tilapia-tomato farm are presented and discussed.

How to Use Fish Behavior Analysis to Sensitively Assess the Hazard Potentials of Environmental Chemicals

Duringl their phylogenesis, all species have adapted to their distinct habitats and to naturally occurring environmental changes. By means of specific long-term self-regulation processes, species are able to react to these environmental changes and therefore maintain their physiological and ecological balance. If these changes take place within biogenetically short periods, species can not develop new strategies of adaptation and the self-regulating mechanism will fail.