201
Fish 1972). Detailed observations of the natural behavior of the Lusitanian toadfish,
a member of the same family (Batrachoididae) with similar reproductive behaviors,
revealed that males avoid sites where a vocalizing male is present (Vasconcelos
et al. 2010). Therefore, we have good indications that both sexes “listen” to conspecific vocalizations. In general, the agonistic sounds produced by both sexes are
broadband pulses rapidly produced in brief bursts (<150 ms) that sound like a
“grunt” (Winn 1972). The reproductive advertisement call is a sustained pulsing (up
to 500 ms) called a “boatwhistle” with a harmonic structure that is a function of the
pulse repetition rate (Watkins 1967). The harmonic structure of the boatwhistle varies somewhat among individuals and populations (Fine 1978; Edds-Walton et al.
2002); however, behavioral studies by Winn (1967) revealed that toadfish respond
equally well to pure-tone sounds around 100–200 Hz. Therefore, the majority of our
research on auditory processing in toadfish has used tonal stimuli rather than pulsed
sounds. There is no doubt that the physiological data collected in our lab reflect
normal auditory processing that functions during natural behavior.
2 Overview of Methods
2.1 Oyster Toadfish
The majority of the fish used for these studies were obtained from the waters around
Woods Hole, MA or Cape Cod, MA by the Marine Resources Center (MRC) at the
Marine Biological Laboratory (MBL). The fish were maintained in large cement
tanks with flow-through local seawater at ambient temperatures in the MRC until
removed to be research subjects. Toadfish chosen for experimentation were placed
in plastic tubs with flow-through, filtered and chilled local seawater (usually 16–18°
C) for at least two weeks. Fish were fed twice weekly with small fish or clam chunks
obtained from the MRC. Fish were not fed for one week prior to use to ensure complete digestion of food to prevent regurgitation and fouling of the gills during anesthesia and to reduce fouling of the water during the experiments.
When local toadfish availability was limited, individuals were obtained from
New Jersey waters by the MRC. Although believed to be the same species, the New
Jersey toadfish were used only for anatomical experiments because their physiology
appeared to differ from the local toadfish (e.g., they required more anesthesia and
metabolized the anesthesia more quickly, possibly due to the warmer temperatures
of their home waters). Therefore, we never used New Jersey toadfish for experiments in which we obtained auditory threshold data. In addition, Massachusetts
toadfish were sometimes retained over the winter in the MRC for use in the spring
months before local toadfish were being caught. Those “overwintered fish” were
used one summer due to a total lack of appropriately sized local fish. The physiological data (e.g., hearing thresholds) from the overwintered fish differed significantly
from the data obtained from freshly caught, local fish (unpublished data); thus, only
anatomical (e.g., recording site) and tract-tracing data from overwintered toadfish
What the Toadfish Ear Tells the Toadfish Brain About Sound
Fish 1972). Detailed observations of the natural behavior of the Lusitanian toadfish,
a member of the same family (Batrachoididae) with similar reproductive behaviors,
revealed that males avoid sites where a vocalizing male is present (Vasconcelos
et al. 2010). Therefore, we have good indications that both sexes “listen” to conspecific vocalizations. In general, the agonistic sounds produced by both sexes are
broadband pulses rapidly produced in brief bursts (<150 ms) that sound like a
“grunt” (Winn 1972). The reproductive advertisement call is a sustained pulsing (up
to 500 ms) called a “boatwhistle” with a harmonic structure that is a function of the
pulse repetition rate (Watkins 1967). The harmonic structure of the boatwhistle varies somewhat among individuals and populations (Fine 1978; Edds-Walton et al.
2002); however, behavioral studies by Winn (1967) revealed that toadfish respond
equally well to pure-tone sounds around 100–200 Hz. Therefore, the majority of our
research on auditory processing in toadfish has used tonal stimuli rather than pulsed
sounds. There is no doubt that the physiological data collected in our lab reflect
normal auditory processing that functions during natural behavior.
2 Overview of Methods
2.1 Oyster Toadfish
The majority of the fish used for these studies were obtained from the waters around
Woods Hole, MA or Cape Cod, MA by the Marine Resources Center (MRC) at the
Marine Biological Laboratory (MBL). The fish were maintained in large cement
tanks with flow-through local seawater at ambient temperatures in the MRC until
removed to be research subjects. Toadfish chosen for experimentation were placed
in plastic tubs with flow-through, filtered and chilled local seawater (usually 16–18°
C) for at least two weeks. Fish were fed twice weekly with small fish or clam chunks
obtained from the MRC. Fish were not fed for one week prior to use to ensure complete digestion of food to prevent regurgitation and fouling of the gills during anesthesia and to reduce fouling of the water during the experiments.
When local toadfish availability was limited, individuals were obtained from
New Jersey waters by the MRC. Although believed to be the same species, the New
Jersey toadfish were used only for anatomical experiments because their physiology
appeared to differ from the local toadfish (e.g., they required more anesthesia and
metabolized the anesthesia more quickly, possibly due to the warmer temperatures
of their home waters). Therefore, we never used New Jersey toadfish for experiments in which we obtained auditory threshold data. In addition, Massachusetts
toadfish were sometimes retained over the winter in the MRC for use in the spring
months before local toadfish were being caught. Those “overwintered fish” were
used one summer due to a total lack of appropriately sized local fish. The physiological data (e.g., hearing thresholds) from the overwintered fish differed significantly
from the data obtained from freshly caught, local fish (unpublished data); thus, only
anatomical (e.g., recording site) and tract-tracing data from overwintered toadfish
What the Toadfish Ear Tells the Toadfish Brain About Sound