396
part of the dorsal or anal fin; PIT tags are injected into the dorsal musculature just
below the juncture of the spinous and soft dorsal fins, and acoustic tags are inserted
into the body cavity through a small incision just anterior and lateral to the vent
region. We use surgical staples or monofilament sutures to close the wound. The
distorted fin ray pattern of regrown amputated fin rays provide a non-specific external tag to alert for the presence of a PIT tag or acoustic tag (if present).
14.4.2 Size, Age, Reproduction and Sound Production
Size structure—Total length (TL, cm) of individual Goliath Grouper is measured
directly on captured fish using a tape measure (straight-line distance from tip of
upper jaw to end of caudal fin) or from digital videos taken underwater using a
video camera equipped with paired green lasers. The two lasers are arranged so that
the beams are parallel and 20 cm apart. During scuba dives, lasers and the attached
video camera are aimed at the fish when it is perpendicular to the beams. The lasers
appear as two green dots on the side of a fish separated by 20 cm. We use dividers
on the video/computer screen in the lab to estimate the total length of each lasermeasured fish. The method is useful for evaluating whether or not there is size or
age selection in the catch. That is, the determination of the age structure of the stock
depends on the assumption that there is no bias in sampling.
Age structure—Murie et al. (2009) provides details of aging Goliath Grouper
using fin rays. Processing involves: cleaning the soft tissue off the cartilaginous
rays, drying the rays, embedding the rays in epoxy, and then sectioning the rays at
widths of about 1.0–1.4 mm. After several sections are mounted to a slide, they are
read under a compound microscope using a green filter which enhances contrast
between translucent and opaque zones of the annuli.
Gonad biopsy and histology—The Goliath Grouper oviduct is very large during
the spawning season, so it is easy to access ovarian tissue using a rather large catheter. We biopsy ovarian tissue with a polyethylene catheter (6.3 mm OD, 4 mm ID),
an in-line plastic collection cup, and a hand-operated vacuum pump (designed for
testing automotive vacuum hoses). The procedure involves inserting a polyethylene
catheter into the oviduct (for males we use a 2 mm OD catheter or small forceps)
while increasing the vacuum with the pump. The tube is drawn back and forth in the
lumen of the ovary so that it continuously removes tissue from the inner wall. The
tube is withdrawn while still under vacuum and the ovarian tissue is sucked into the
collection cup. We preserved gonad tissue immediately in 10% formalin. After several days of fixing, the tissues are processed using standard histological procedures,
then examined for reproductive condition.
Sound production—We use acoustic recordings as additional verification of
Goliath Grouper spawning activity at selected sites. Night-time sounds are produced in a lunar pattern only on spawning sites and only during the spawning season
(Mann et al. 2009, Koenig et al. 2016). We record Goliath Grouper sounds using a
DSG-Ocean (http://loggerheadinstruments.com/) or a H2n recorder and an H2a
M. Hostim-Silva et al.
part of the dorsal or anal fin; PIT tags are injected into the dorsal musculature just
below the juncture of the spinous and soft dorsal fins, and acoustic tags are inserted
into the body cavity through a small incision just anterior and lateral to the vent
region. We use surgical staples or monofilament sutures to close the wound. The
distorted fin ray pattern of regrown amputated fin rays provide a non-specific external tag to alert for the presence of a PIT tag or acoustic tag (if present).
14.4.2 Size, Age, Reproduction and Sound Production
Size structure—Total length (TL, cm) of individual Goliath Grouper is measured
directly on captured fish using a tape measure (straight-line distance from tip of
upper jaw to end of caudal fin) or from digital videos taken underwater using a
video camera equipped with paired green lasers. The two lasers are arranged so that
the beams are parallel and 20 cm apart. During scuba dives, lasers and the attached
video camera are aimed at the fish when it is perpendicular to the beams. The lasers
appear as two green dots on the side of a fish separated by 20 cm. We use dividers
on the video/computer screen in the lab to estimate the total length of each lasermeasured fish. The method is useful for evaluating whether or not there is size or
age selection in the catch. That is, the determination of the age structure of the stock
depends on the assumption that there is no bias in sampling.
Age structure—Murie et al. (2009) provides details of aging Goliath Grouper
using fin rays. Processing involves: cleaning the soft tissue off the cartilaginous
rays, drying the rays, embedding the rays in epoxy, and then sectioning the rays at
widths of about 1.0–1.4 mm. After several sections are mounted to a slide, they are
read under a compound microscope using a green filter which enhances contrast
between translucent and opaque zones of the annuli.
Gonad biopsy and histology—The Goliath Grouper oviduct is very large during
the spawning season, so it is easy to access ovarian tissue using a rather large catheter. We biopsy ovarian tissue with a polyethylene catheter (6.3 mm OD, 4 mm ID),
an in-line plastic collection cup, and a hand-operated vacuum pump (designed for
testing automotive vacuum hoses). The procedure involves inserting a polyethylene
catheter into the oviduct (for males we use a 2 mm OD catheter or small forceps)
while increasing the vacuum with the pump. The tube is drawn back and forth in the
lumen of the ovary so that it continuously removes tissue from the inner wall. The
tube is withdrawn while still under vacuum and the ovarian tissue is sucked into the
collection cup. We preserved gonad tissue immediately in 10% formalin. After several days of fixing, the tissues are processed using standard histological procedures,
then examined for reproductive condition.
Sound production—We use acoustic recordings as additional verification of
Goliath Grouper spawning activity at selected sites. Night-time sounds are produced in a lunar pattern only on spawning sites and only during the spawning season
(Mann et al. 2009, Koenig et al. 2016). We record Goliath Grouper sounds using a
DSG-Ocean (http://loggerheadinstruments.com/) or a H2n recorder and an H2a
M. Hostim-Silva et al.