FISH NUTRITION
411
These effects may be of especial interest to fish producers because,
other than in brood stock, suppression of gonad development is
desirable-less nutrient is diverted from the production of flesh.
Besides, when rainbow trout are farmed in sea water (not an uncommon practice nowadays) high mortalities frequently occur at
spawning, especially among the male population, possibly because of
the osmotic stress. Thus compounds which suppress gonad maturation
until the fish is beyond marketable size are potentially very useful.
Unfortunately dosage levels of 4-chlorotestosterone which resulted
in the highest growth rates in rainbow trout had an additional side
effect-marked hypertrophy of liver cells occurred together with glycogen deposition. Whether this gluconeogenesis can be avoided by
dietetic modification has not yet been explored.
Another area worthy of investigation is that of steroid-like
compounds in which the growth promoting and gonad suppressing
actions are divorced from hepatotrophic and renotrophic side effects.
Another organic compound which has received some attention from
fish nutritionists is diethyl stilboestrol, a substance with oestrogenic
activity. Early research revealed that subcutaneous implantation of
diethyl stilboestrol pellets in livestock (chickens, lambs) led to greatly
improved gains and feed eBciency. In the middle fifties it wa;s shown
that minute quantities of diethyl stilboestrol added to the diet of cattle
markedly increased rate of gain and feed efficiency. On average the
rate of gain was increased by 13%.
The oral application of stilboestrol to fish has therefore been
investigated but has given variable results depending on the dosage
level. Ghittino (1970) fed trout a number of commercial feeds containing
diethyl stilboestrol at levels of 5 g and 500g per 100 kg of pellets.
Fish were fed at the rate of 1% of their body weight per day so that
they received from 50 pg to 5 mg diethyl stilboestrol/lOOg live
weightlday. Growth of trout receiving these levels of diethyl stilboestrol
was lower than that of controls.
In experiments with 0-group plaice much lower levels of diethyl
stilboestrol were used ranging from 120 to 500 mg diethyl stilboestrol
per 100 kg dry ration (Table VII). The fish consumed 1% of their live
weight per day and thus received 1.2 to 5.0 pg/lOO g live weightlday.
Thirty individually marked fish were used on each treatment and as
we have consistently found that larger fish grow faster (Cowey et at.,
1971) we have considered fish of different initial weight separately.
At the lowest treatment level there is a marked growth promoting
action of diethyl stilboestrol with no undesirable side effects apparent
during the ten week feeding period. The contrast between our
411
These effects may be of especial interest to fish producers because,
other than in brood stock, suppression of gonad development is
desirable-less nutrient is diverted from the production of flesh.
Besides, when rainbow trout are farmed in sea water (not an uncommon practice nowadays) high mortalities frequently occur at
spawning, especially among the male population, possibly because of
the osmotic stress. Thus compounds which suppress gonad maturation
until the fish is beyond marketable size are potentially very useful.
Unfortunately dosage levels of 4-chlorotestosterone which resulted
in the highest growth rates in rainbow trout had an additional side
effect-marked hypertrophy of liver cells occurred together with glycogen deposition. Whether this gluconeogenesis can be avoided by
dietetic modification has not yet been explored.
Another area worthy of investigation is that of steroid-like
compounds in which the growth promoting and gonad suppressing
actions are divorced from hepatotrophic and renotrophic side effects.
Another organic compound which has received some attention from
fish nutritionists is diethyl stilboestrol, a substance with oestrogenic
activity. Early research revealed that subcutaneous implantation of
diethyl stilboestrol pellets in livestock (chickens, lambs) led to greatly
improved gains and feed eBciency. In the middle fifties it wa;s shown
that minute quantities of diethyl stilboestrol added to the diet of cattle
markedly increased rate of gain and feed efficiency. On average the
rate of gain was increased by 13%.
The oral application of stilboestrol to fish has therefore been
investigated but has given variable results depending on the dosage
level. Ghittino (1970) fed trout a number of commercial feeds containing
diethyl stilboestrol at levels of 5 g and 500g per 100 kg of pellets.
Fish were fed at the rate of 1% of their body weight per day so that
they received from 50 pg to 5 mg diethyl stilboestrol/lOOg live
weightlday. Growth of trout receiving these levels of diethyl stilboestrol
was lower than that of controls.
In experiments with 0-group plaice much lower levels of diethyl
stilboestrol were used ranging from 120 to 500 mg diethyl stilboestrol
per 100 kg dry ration (Table VII). The fish consumed 1% of their live
weight per day and thus received 1.2 to 5.0 pg/lOO g live weightlday.
Thirty individually marked fish were used on each treatment and as
we have consistently found that larger fish grow faster (Cowey et at.,
1971) we have considered fish of different initial weight separately.
At the lowest treatment level there is a marked growth promoting
action of diethyl stilboestrol with no undesirable side effects apparent
during the ten week feeding period. The contrast between our