422
The Biology of Sea Turtles, Vol. II
emphasis on benthos (Bjorndal, 1997). Gut content analysis studies have been done
on all sea turtle species cataloging food items consumed (Bjorndal, 1997), but little
is known about actual wild feeding rates. In captivity, overfed turtles and turtles fed
ad libitum are prone to obesity, fatty degeneration of the liver (Solomon and Lippett,
1991), and bloating.
Captive sea turtle diets vary considerably, ranging from natural foods (whole
fish) to commercially prepared dry pelleted diets. Blends of natural foods (i.e., fish,
shrimp, squid, crab, scallops), often supplemented with vitamins, are popular diets
in zoos and aquaria. Blends may be prepared fresh each day or prepared in bulk and
kept frozen until needed. Mixtures of natural foods may contain gelatinous binders
to keep food from dispersing in the water prior to consumption by the sea turtles
(Jones et al., 2000; Cong and Wang, 1997). To produce the same growth as dry
pelleted foods, wet food is offered at a rate of up to five times that of dry food to
compensate for the difference in moisture content. Wet feed rates vary from maintenance diets of 1% body weight per week (Higgins, unpublished data) to production–growth diets of 12–15% per day (Sumano Lopez et al., 1980). Feeding to
satiation has also been reported with leatherback hatchlings (Jones et al., 2000).
The NMFS STF feeds a natural maintenance diet (whole mackerel) to loggerheads at 1% body weight per week when trying to maintain turtles at a specific size
for research. Fasting days are common in aquaria. One or two days without food
helps promote an appetite and may help maintain water quality. The NMFS STF
feeds six days per week. Turtles maintained in aquaria with other animals may
become very aggressive and compete for food. Turtles may attempt to consume all
food introduced into the tank, resulting in overfeeding and leading to obesity. Feeding
demonstrations are popular attractions at aquaria, and aggressive feeding by turtles
may put divers at risk of injury. It may be necessary to distract or isolate turtles
while the rest of the tank is fed.
Most large captive-rearing facilities feed some form of commercially prepared
pelletized feed consisting of 25–45% crude protein, and 3.9–12% fat, 3.22–8.58% fiber
(Caillouet et al., 1989; Wood and Wood, 1980; Wood, 1980). Higher protein levels
result in greater growth (Wood, 1980; Caillouet et al., 1989). The protein source and
content of the feed typically drives the feed cost; higher protein content commands a
higher price, and protein from fish meal is more expensive than plant protein. Although
weight gains of turtles fed fish versus plant protein sources are similar (Higgins, unpublished data), those turtles fed the fish meal source appeared to be more robust (Higgins,
unpublished data). Diets containing soy products, especially those utilizing soy as the
primary protein source, may increase estrogen levels in the blood (Shaw et al., 1989).
Soybeans contain high levels of phytoestrogen. Increased phytoestrogen levels in
humans have been linked to liver disease and reproductive problems (Shaw et al., 1989).
Several commercially available diet formulations have been successfully used over
the years (Wood, 1991; Wood and Wood, 1980; Caillouet et al., 1989). Currently, the
NMFS STF turtles are fed Aquamax ® 500 Grower (PMI Nutrition International, Inc.,
Brentwood, MO). This is a dry, 4.7-mm (3/16 in.) diameter extruded pellet, which is
small enough to be consumed by all sized turtles. The pellets float and remain intact
in seawater. Pellet food should be bought in small quantities and kept frozen until use
to preserve freshness, and prevent mold and rodent and insect infestation. Wet diets
1123_C16 Page 422 Tuesday, November 12, 2002 8:28 AM
The Biology of Sea Turtles, Vol. II
emphasis on benthos (Bjorndal, 1997). Gut content analysis studies have been done
on all sea turtle species cataloging food items consumed (Bjorndal, 1997), but little
is known about actual wild feeding rates. In captivity, overfed turtles and turtles fed
ad libitum are prone to obesity, fatty degeneration of the liver (Solomon and Lippett,
1991), and bloating.
Captive sea turtle diets vary considerably, ranging from natural foods (whole
fish) to commercially prepared dry pelleted diets. Blends of natural foods (i.e., fish,
shrimp, squid, crab, scallops), often supplemented with vitamins, are popular diets
in zoos and aquaria. Blends may be prepared fresh each day or prepared in bulk and
kept frozen until needed. Mixtures of natural foods may contain gelatinous binders
to keep food from dispersing in the water prior to consumption by the sea turtles
(Jones et al., 2000; Cong and Wang, 1997). To produce the same growth as dry
pelleted foods, wet food is offered at a rate of up to five times that of dry food to
compensate for the difference in moisture content. Wet feed rates vary from maintenance diets of 1% body weight per week (Higgins, unpublished data) to production–growth diets of 12–15% per day (Sumano Lopez et al., 1980). Feeding to
satiation has also been reported with leatherback hatchlings (Jones et al., 2000).
The NMFS STF feeds a natural maintenance diet (whole mackerel) to loggerheads at 1% body weight per week when trying to maintain turtles at a specific size
for research. Fasting days are common in aquaria. One or two days without food
helps promote an appetite and may help maintain water quality. The NMFS STF
feeds six days per week. Turtles maintained in aquaria with other animals may
become very aggressive and compete for food. Turtles may attempt to consume all
food introduced into the tank, resulting in overfeeding and leading to obesity. Feeding
demonstrations are popular attractions at aquaria, and aggressive feeding by turtles
may put divers at risk of injury. It may be necessary to distract or isolate turtles
while the rest of the tank is fed.
Most large captive-rearing facilities feed some form of commercially prepared
pelletized feed consisting of 25–45% crude protein, and 3.9–12% fat, 3.22–8.58% fiber
(Caillouet et al., 1989; Wood and Wood, 1980; Wood, 1980). Higher protein levels
result in greater growth (Wood, 1980; Caillouet et al., 1989). The protein source and
content of the feed typically drives the feed cost; higher protein content commands a
higher price, and protein from fish meal is more expensive than plant protein. Although
weight gains of turtles fed fish versus plant protein sources are similar (Higgins, unpublished data), those turtles fed the fish meal source appeared to be more robust (Higgins,
unpublished data). Diets containing soy products, especially those utilizing soy as the
primary protein source, may increase estrogen levels in the blood (Shaw et al., 1989).
Soybeans contain high levels of phytoestrogen. Increased phytoestrogen levels in
humans have been linked to liver disease and reproductive problems (Shaw et al., 1989).
Several commercially available diet formulations have been successfully used over
the years (Wood, 1991; Wood and Wood, 1980; Caillouet et al., 1989). Currently, the
NMFS STF turtles are fed Aquamax ® 500 Grower (PMI Nutrition International, Inc.,
Brentwood, MO). This is a dry, 4.7-mm (3/16 in.) diameter extruded pellet, which is
small enough to be consumed by all sized turtles. The pellets float and remain intact
in seawater. Pellet food should be bought in small quantities and kept frozen until use
to preserve freshness, and prevent mold and rodent and insect infestation. Wet diets
1123_C16 Page 422 Tuesday, November 12, 2002 8:28 AM