Elsevier

Water Research

Volume 38, Issue 12, July 2004, Pages 2891-2897
Water Research

A field methodology to study effects of UV radiation on fish larvae

https://doi.org/10.1016/j.watres.2004.04.004Get rights and content

Abstract

There is a considerable lack of in situ specific information about the effects of UV-B radiation on limnic animals studied in the field. We exposed larval pike (Esox lucius L.) in two types of cuvettes (glass and quartz) placed at different depths (5 or 15 cm) to natural solar UV or to artificially enhanced UV-B (lamps on 3 h per day), simulating the scenarios for coming decades. Dose realism and comparability with earlier laboratory experiments was the main purpose, and therefore UV-B irradiances to the surface as well as underwater irradiances were directly measured. Result showed that UV-B dose rates in natural waters are low even though DOC concentration was low (4.8 mg/l) in our study lake. A slight increase in ambient UV-B dose rates was enough to cause neurobehavioral symptoms in pike larvae. However, the dose rates applied were inadequate to affect superoxide dismutase (SOD) or HSP70. While assessing the suggested risks due to increased UV, conclusions emphasize the importance of conducting field UV studies as supplements to laboratory experiments. We also recommend direct measurements of UV-radiation at sites where the target organisms are actually exposed.

Introduction

Long-term data series on solar UV-B radiation (290–315 nm) incident at the earth's surface suggest that ultraviolet-B (UV-B) levels have increased over the past two decades due to stratospheric ozone depletion [1], [2], [3]. Related to climatic change, even 50% increase in CIE-weighted doses have been predicted in northern latitudes in coming decades [3].

In freshwater lakes, attenuation depths for ultraviolet radiation may range from a few centimeters in waters having high concentrations of dissolved organic carbon (DOC) to over 10 m or more in some of the lowest DOC lakes [4], [5], [6]. In the clearest lakes in Finland, UV-B can penetrate deeper than 1 m [6]. Further, changes in UV-B may interact with other environmental factors such as acidification, precipitation and temperature changes. In combination with several factors, decreases in concentration of dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM) in waters modifies the penetration of solar radiation in marine and freshwaters [4], [5], [7], [8].

Harmful effects of UV-B on fishes have been studied extensively under laboratory conditions [9], [10], [11], [12], [13]. However, only a very few field studies with the proper UV dosimetry exist [14], [15], [16], [17], [18]. The same is true for other organisms. For example, numerous field UV-B studies with frogs have been done, showing impaired development and lethality of eggs and larvae (reviewed in [19], [20] but only a few good reports have directly measured UV-B [21], [22], [23], [24]. In order to assess the margins of safety between current and predicted UV-B conditions, more field experimentations are needed. Due to inherent spectral deficiencies of artificial light sources, laboratory experiments ought to be considered only as first approximations of realism in nature.

In northern boreal latitudes in Fennoscandia, the highest relative increase in UV-B radiation is in spring at the time just preceding the most intensive reproductive phase of several fishes. One of those species is the northern pike (Esox lucius L.), investigated in this study. It spawns April–May in shallow littoral waters (water depth under 1 m) and larvae use these habitats as nurseries for several weeks after hatching [25]. Therefore, during early developmental stages pike larvae can be exposed to episodes of high UV-B. Recently, under laboratory conditions increased in mortality with severe neurobehavioral disorders with pike was demonstrated at very low dose levels [26].

Induction of HSP70 was measured since it would serve as a biomarker of cellular stress [28]. The role of HSP70 induction is considered to be adaptive as it is one protective mechanism against apoptotic cell death [29], [30], [31]. HSP70 is responsible for correct folding of cell proteins under normal or stress conditions [39], [40]. In our previous study UV-B induced HSP70 in whitefish [32], whereas in pike HSP70 levels decreased after exposure to low UV dose [26].

The activity of SOD was determined from studies with fish larvae, indirectly indicating formation of superoxide anion and oxidative stress [33]. Superoxide dismutase (SOD), catalysing the dismutation of superoxide anion into hydrogen peroxide and molecular oxygen [33], provides one important protective mechanism in living cells. Regarding adaptive biochemistry, there are only a few studies with fishes where impact of UV-B on antioxidant status is assessed [34].

The purpose of this study was to examine with field experiment if UV-B radiation will affect larval pike at current levels or at those predicted in the future. Present work actually is one of the few in situ exposures of fish larvae to natural sunlight. In the study larvae were exposed under field conditions to either natural solar UV alone or with artificially enhanced UV-B. The aim was to investigate whether or not solar UV-B irradiance could cause neurobehavioral symptoms, with some sublethal endpoints, observed earlier under laboratory conditions [26]. We hypothesized that the effects in the field were largely similar observed in the laboratory. The dose realism and comparability were the main purpose and therefore UV-B irradiances at the water surface as well as underwater irradiances were measured directly during the experiment.

Section snippets

Materials and methods

Field UV exposures with pike were conducted in May 2002 in Lake Palosjärvi, Finland (62°03′ N, 26°21′ E), which is optically very clear water basin. Newly hatched larvae (<48 h) of northern pike were used as test animals (Lake Arvaja stock). Before hatching, the fertilized eggs (pooled from 4 pairs) were incubated at 10°C in cylindrical glass funnels with upstream water flow. Once hatched, larvae transferred to aquaria and acclimated to 11–12°C during the first 24 h after hatching. The next day

Results

UV measurements showed that water attenuated UV-B very efficiently (Table 1, Fig. 3) in our study lake. The intensity of UV-B (290–315 nm) at 5 cm depth was about 42% from surface irradiance, and larvae inside quartz cuvettes were exposed to a maximum UV-B intensity of 0.4 W/m2. However, this includes seven percent that did not penetrate through the quartz wall, resulting in a CIE-weighted UV dose of 0.9 kJ/m2 in three hours time. The maximum doses inside two types of cuvettes placed underwater at

Discussion

There is a considerable lack of information on the effects of UV-B radiation on boreal aquatic animals under field conditions. Instead, numerous laboratory studies have shown detrimental effects of UV [9], [10], [11], [12], but these never exactly simulate ambient solar radiation. Present work is one of the few in situ exposures of fish larvae to natural sunlight.

Present field experiments with pike suggest that a minor increase to ambient UV-B received by the earth's surface might cause

Conclusions

While assessing the suggested risks due to increased UV, it should be emphasized the importance of conducting field UV studies as supplements to laboratory experiments. We also recommend direct measurements of UV-radiation at sites where the target organisms actually are exposed, and especially underwater measurements. The frequency of neurobehavioral disorders was considerably lower in field than in laboratory. Accordingly, no biochemical changes were observed. Present field experiments with

Acknowledgments

We thank Ms. Mervi Koistinen for assistance in conducting experiments and laboratory analysis, as well as Mr. Hannu Kautto and M.Sc. Jami Saarnivaara helping to build up the experimentation dock. This research was supported by the Maj and Tor Nessling foundation and the Academy of Finland (Figare/Solar-project).

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