hardness) should be measured and reported, and the medium should be screened
beforehand for contamination. If contamination is present, it is important to record
the concentrations of the specific contaminant to identify the background level, to
have a better understanding of the possible effects. This is especially noteworthy
when river water is used to acclimate the organisms, in particular for in situ
experiments where river water mimics natural environmental conditions for the
acclimation period. It is difficult to say how long the acclimation should last. The
authors recommend that further research is required to determine the impact of time
frame on acclimation periods and to determine if a longer acclimation period results
in stronger data with a lower level of variability.
Several different food types have been highlighted during this review, including
different leaf species and conditioning methods. Even though Gammarids are biologically omnivorous organisms, a leaf-based diet is recommended in feeding
studies, both during the acclimation period and the exposure, and the same food
should be used for both (i.e. same leaf species and same preparation). Alnus spp. are
the most commonly used leaf material for freshwater Gammarid feeding studies. The
authors therefore recommend Alnus spp. as a standardised food source for ecotoxicological assays. However, the distribution of Alnus spp. is not ubiquitous around
the world, and therefore it might be challenging for some researchers to source them
for their experiments. In such situations, industrial feed might be a better solution to
overcome the problem of non-standardisation. If leaf material is used, applying a
conditioning process is recommended, since conditioned material has been proven to
be more palatable and have a lower C:N, which translates to a better energy supply.
Moreover, it has also been demonstrated how leaf palatability increases when they
are conditioned for longer time periods. Consequently, a short conditioning period
(i.e. a few days) should be avoided, and organisms should be fed on leaves
conditioned for at least 10 days. However, this time period should be prolonged if
using fresh leaf material, since it has been reported that conditioning takes longer. In
ex situ experiments, conditioning should be conducted using an artificial media
inoculated with Cladosporium spp., which is the most common fungi species used
in the literature to condition leaves. This will ultimately reduce the likelihood of
contamination that might result from using river detritus as a source of fungi
inoculum for conditioning leaves.
On the other hand, for in situ studies, the conditioning process should ultimately
replicate, as accurately as possible, real-life environmental conditions and processes,
which means using river water, inoculum and Gammarids from the study site. As
previously mentioned, the composition of the water needs to be identified and also
the chemical parameters; the latter could then be replicated during the conditioning
process. For in situ experiments, the authors recommend conditioning the leaf
material directly in the river. For example, placing leaves in small net bags that are
submerged and secured in the river where the experiment would take place. This
would provide the Gammarids with the same type of food during the acclimation
period and exposure. However, conditioning takes time, so it should be undertaken
well in advance of the experiment.
34
G. Consolandi et al.
beforehand for contamination. If contamination is present, it is important to record
the concentrations of the specific contaminant to identify the background level, to
have a better understanding of the possible effects. This is especially noteworthy
when river water is used to acclimate the organisms, in particular for in situ
experiments where river water mimics natural environmental conditions for the
acclimation period. It is difficult to say how long the acclimation should last. The
authors recommend that further research is required to determine the impact of time
frame on acclimation periods and to determine if a longer acclimation period results
in stronger data with a lower level of variability.
Several different food types have been highlighted during this review, including
different leaf species and conditioning methods. Even though Gammarids are biologically omnivorous organisms, a leaf-based diet is recommended in feeding
studies, both during the acclimation period and the exposure, and the same food
should be used for both (i.e. same leaf species and same preparation). Alnus spp. are
the most commonly used leaf material for freshwater Gammarid feeding studies. The
authors therefore recommend Alnus spp. as a standardised food source for ecotoxicological assays. However, the distribution of Alnus spp. is not ubiquitous around
the world, and therefore it might be challenging for some researchers to source them
for their experiments. In such situations, industrial feed might be a better solution to
overcome the problem of non-standardisation. If leaf material is used, applying a
conditioning process is recommended, since conditioned material has been proven to
be more palatable and have a lower C:N, which translates to a better energy supply.
Moreover, it has also been demonstrated how leaf palatability increases when they
are conditioned for longer time periods. Consequently, a short conditioning period
(i.e. a few days) should be avoided, and organisms should be fed on leaves
conditioned for at least 10 days. However, this time period should be prolonged if
using fresh leaf material, since it has been reported that conditioning takes longer. In
ex situ experiments, conditioning should be conducted using an artificial media
inoculated with Cladosporium spp., which is the most common fungi species used
in the literature to condition leaves. This will ultimately reduce the likelihood of
contamination that might result from using river detritus as a source of fungi
inoculum for conditioning leaves.
On the other hand, for in situ studies, the conditioning process should ultimately
replicate, as accurately as possible, real-life environmental conditions and processes,
which means using river water, inoculum and Gammarids from the study site. As
previously mentioned, the composition of the water needs to be identified and also
the chemical parameters; the latter could then be replicated during the conditioning
process. For in situ experiments, the authors recommend conditioning the leaf
material directly in the river. For example, placing leaves in small net bags that are
submerged and secured in the river where the experiment would take place. This
would provide the Gammarids with the same type of food during the acclimation
period and exposure. However, conditioning takes time, so it should be undertaken
well in advance of the experiment.
34
G. Consolandi et al.