THE ARTIFICIAL PROPAOATION OF MARINE FISH
63
water ; there was no temperature or bacterial control. Two tanks were
stocked with 10 000 pond-spawned plaice eggs each; the other pair
with 20 000 eggs. Survivals were remarkably consistent (Table VII).
The dose agreement between percentage survivals in both lightly and
heavily stocked b n k s suggests that the maximum egg stocking rate
jn tanks of this size is in excess of 20 000. Although the mean survival
of 30% was very similar to survivals in control tanka of the baoteriological experiment (Fig. la), the survivor density of 7570 young M / m *
exceeded all expectations, and encourages the view that a hatchery
designed to produoe 1 million metamorphosed plaice annually would
not be unduly large. However, a high incidence of pigment abnormality
occurred among surviving stocks in all four tanks. Pigment peculiarities will be discussed in the next section of this paper.
0. Larval feeding studies: 1962
If any particular discovery can be singled out as a breakthrough ”
in the problem of rearing marine fish, it is surely the use of Artemia
nauplii as a larval food, by Rollefsen (1939). Progress is now being
made towards designing 8 prototype Artemia production system
capable of being expanded to meet mass-production requirements.
This work is in the hands of my colleague, Mr. J. D. Riley, who also
carried out the first of a series of larval feeding experiments, at Port
Erin in 1962. His findings will be published in full at a later date;
in the meantime, they are briefly reviewed in the following progress
report :
(a) The percentage of plaice larvae surviving the first-feeding stage
is increased in conditions of food surplus. After feeding is well
established, surplus food is not advantageous end is therefore
wasteful. It also creates problems of tank hygiene.
(a) Larval growth rates do not seem to be affected until Artemia
rations are reduced below 75% of the feeding capaoity of a
stock.
(c) When rations are reduced below 60% feeding capacity, percentage survival decreases, while the incidence of pigment
abnormality among metamorphosed survivors increesee.
(4 Maximum feeding occurs during the late pelagio stage 3, when
the mean number of Artemia nauplii eaten per fish may reach
200 per day.
(e) Stage 3 larvaa can withstand food deprivation for 6 days
without mortality, but 60% of a starved experimental stock
(200 larvae) died within 18 days. The survivora were offered
c.
63
water ; there was no temperature or bacterial control. Two tanks were
stocked with 10 000 pond-spawned plaice eggs each; the other pair
with 20 000 eggs. Survivals were remarkably consistent (Table VII).
The dose agreement between percentage survivals in both lightly and
heavily stocked b n k s suggests that the maximum egg stocking rate
jn tanks of this size is in excess of 20 000. Although the mean survival
of 30% was very similar to survivals in control tanka of the baoteriological experiment (Fig. la), the survivor density of 7570 young M / m *
exceeded all expectations, and encourages the view that a hatchery
designed to produoe 1 million metamorphosed plaice annually would
not be unduly large. However, a high incidence of pigment abnormality
occurred among surviving stocks in all four tanks. Pigment peculiarities will be discussed in the next section of this paper.
0. Larval feeding studies: 1962
If any particular discovery can be singled out as a breakthrough ”
in the problem of rearing marine fish, it is surely the use of Artemia
nauplii as a larval food, by Rollefsen (1939). Progress is now being
made towards designing 8 prototype Artemia production system
capable of being expanded to meet mass-production requirements.
This work is in the hands of my colleague, Mr. J. D. Riley, who also
carried out the first of a series of larval feeding experiments, at Port
Erin in 1962. His findings will be published in full at a later date;
in the meantime, they are briefly reviewed in the following progress
report :
(a) The percentage of plaice larvae surviving the first-feeding stage
is increased in conditions of food surplus. After feeding is well
established, surplus food is not advantageous end is therefore
wasteful. It also creates problems of tank hygiene.
(a) Larval growth rates do not seem to be affected until Artemia
rations are reduced below 75% of the feeding capaoity of a
stock.
(c) When rations are reduced below 60% feeding capacity, percentage survival decreases, while the incidence of pigment
abnormality among metamorphosed survivors increesee.
(4 Maximum feeding occurs during the late pelagio stage 3, when
the mean number of Artemia nauplii eaten per fish may reach
200 per day.
(e) Stage 3 larvaa can withstand food deprivation for 6 days
without mortality, but 60% of a starved experimental stock
(200 larvae) died within 18 days. The survivora were offered
c.