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ESTABLISHING
PHYSIOLOGICAL INDICES FOR MORE EFFECTIVE USE OF TFM TO CONTROL SEA
LAMPREY POPULATIONS
IN THE GREAT LAKES.
July 2014
ABSTRACT:
The lampricide,
3-trifluoromethyl-4-nitrophenol (TFM) has been effectively used to control
invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes for over 50
years. It is now clearly established that TFM interferes with mitochondrial ATP
production in both sea lamprey and in the rainbow trout (Oncorhynchus
mykiss), leading to a mismatch between ATP supply
and demand that can eventually result in the depletion of energy reserves and
death. The specificity of TFM is related to the relative inability of larval
sea lampreys to detoxify and eliminate TFM from their bodies compared to most
non-target fishes. However, in some instances non-target fishes may experience
adverse effects, toxicity and mortality during routine applications of TFM.
Accordingly, the objectives of this project were to: (I) more fully
explain why TFM is selective to sea lamprey compared to non-target fishes such
as the rainbow trout and lake sturgeon (Acipenser
fulvescens), (II) determine if routine
application of TFM resulted in significant adverse physiological disturbances
in non-target fishes and to determine if such effects were reversible, (III)
ascertain howchanges in season and nutritional
status affected the TFM sensitivity of lampreys.
To better understand how TFM is detoxified and
eliminated, sea lampreys, rainbow trout and lake sturgeon were exposed to
either the TFM LC100 (MLC; median lethal concentration) or the TFM LC50 of
larval sea lampreys (lake sturgeon only) for up to 12 h, and the concentrations
of TFM and its detoxification product, TFM-glucuronide,
quantified in the carcasses of the animals using solid phase extraction and
HPLC. Not surprisingly, TFM was quickly taken-up by all 3 groups, but sea
lamprey did not detoxify TFM through the formation of TFM-glucuronide.
As a result, TFM was eliminated slowly over several hours by sea lamprey during
depuration in TFM-free water. In contrast, rainbow trout and lake sturgeon
readily converted TFM to TFM-glucuronide, which was
rapidly eliminated within 3 h, along with the parent compound, during recovery.
Accompanying experiments using radio-labelled TFM (14C-TFM)
indicated that TFM was more rapidly taken-up by larval sea lampreys in more
alkaline waters (pH 8.5) compared to circumneutral pH
(pH 7.8) and acidic water (pH 6.5), due a greater proportion of TFM being its
un-ionized, more lipophilic phenolic
form at higher pH. These findings strongly suggest
TFM is taken-up in its un-ionized form by diffusion down water-blood TFM
gradients. Despite relatively slow rates of TFM elimination, sea lamprey were
still able to recover from short bouts of TFM exposure (4 or 6 h), as
demonstrated by the restoration of brain and liver glycogen reserves, phosphocreatine concentrations and the elimination of
lactate within 4 h of recovery. Collectively, these findings confirm that while
sea lampreys have a lower capacity to detoxify TFM, they can recover from
short-term TFM exposure, which could lead to treatment residuals if the animals
are able to temporarily avoid full TFM doses or if TFM treatments are
interrupted.
TFM had relatively few adverse effects in rainbow
and lake sturgeon. Reductions in liver glycogen were observed in rainbow trout,
and were likely related to increased glycogen requirements due to the need to
make up for a shortfall in ATP supply, which was likely compromised, even at
the sub-lethal concentrations of TFM to which the fish were exposed. Similar
reductions in TFM were not observed in lake sturgeon because they were exposed
to lower TFM concentrations. The reductions in liver glycogen in rainbow trout
may partially explain why aerobic swim performance was impaired following TFM
exposure, as demonstrated by a 28 % reduction in the critical swimming velocity
(Ucrit).
In the field, however, it is likely that liver
glycogen stores would be rapidly replenished with the resumption of feeding. Surprisingly,
anaerobic, burst swim performance was not compromised, and actually improved
slightly 4 h following TFM exposure. Light microscopy revealed that exposure to
TFM caused minimal damage to the gills. Subsequent measurements of Na+/K+-ATPase and H+-ATPase (V-ATPase) activity and quantity using western blotting, and measurements
of unidirectional Na+ movements across the gills indicated that TFM had minimal
effects on gillmediated ion regulation in trout and
sturgeon in hard water.
To determine how changes in season and physiological
condition affected the TFM sensitivity of larval lampreys to TFM, animals were
captured in May, June, August and September of 2011 and subjected to acute
toxicity tests at the Hammond Bay Biological Station within 5-10 d of capture.
Subsequent determination of the 12 h LC50s, indicated that the animals captured
in the spring at temperatures of approximately 12°C were most sensitive to TFM,
with the 12 h LC50 increasing by almost 3-fold by August, when water
temperatures were warmest (~ 22°C). The greater sensitivity of the larval sea
lamprey to TFM in the spring appeared to be related to 75 % lower glycogen
stores in the muscle, and 40 % lower glycogen stores in the brain, along with
greatly reduced lipid reserves, compared to the animals captured later in the
year. These findings suggest that there is justification for altering the
timing of applications to take advantage of the greater sensitivity of larval
lampreys in the spring, particularly in rivers containing large water volumes and
flows, which could reduce overall TFM use. Extra vigilance, however, may be
required in the summer to guard against treatment residuals, when the larval
lampreys are most robust, larger and tolerant to TFM. Indeed, accompanying
experiments exploring how body size impacted TFM sensitivity demonstrated that
there was a significant positive correlation between TFM tolerance, body mass
and length, but not condition factor.
In conclusion, the present project demonstrates that
the effectiveness of TFM treatments is affected by a variety of abiotic and biotic factors. Consideration of these factors
and incorporating this knowledge into TFM treatment regimens will allow sea
lamprey control supervisors to conserve TFM use and minimize the risk of
treatment residuals.
Although non-target rainbow trout and lake sturgeon
have efficient means to detoxify TFM, and suffered few adverse effects during
TFM exposure, further studies are required to more accurately determine how
life stage, environmental factors and nutritional status affect their capacity
to deal with this lampricide..