THE ARTIFIOIAL PROPAQATION OF MARINE FISH
69
population density is probably linked with a second relationship given
in Fig. 24, showing that smaller survivors among a stock usually have
less pigment cover than their larger contemporaries. It has already
been demonstrated that densely populated tanks 8r6 biased in favour
of smaller larvae (Figs. 19 and 20). With the exception of tank 1,
1960 (ringed in Fig. 23), all tanks were of equal size and egg stocking
rate. Figure 23 therefore incidentally compares mean d o d pigment
cover with the degree of survival in each tank. Heavier pigmentation
among less-dense tank populations could equally well be explained by
the differential mortality of imperfectly pigmented runts. Experiments
in 1962 also suggest some relationship between the degree of pigmentation at metamorphosis, and the temperature rbgime during incubation
and larval development. Food abundance might also be important
(J. D. Riley, personal communication).
It looks as if chromatophore development during organogeny is a
particularly sensitive and delicate process, easily disrupted by an
unfavourable environment. Heuts (1963) made this point with reference
to the regressive evolution of Cuecobarbus geertsii Boulenger, the blind
cave fish of the Congo. Norman (1934) and Follet (1954), on the other
hand, related the piebald condition in flatfish to vertebral damage,
whilst von Ubisch (1962) considered light intensity to be important.
The tank environment, involving surface contact and " community "
conditions, is completely foreign to the pelagic plaice larva, and it
says a great deal for the innate adaptability of the species, that high
survivals to metamorphosis can be achieved, even though abnormalities
commonly occur.
Since effective hatchery production (if intended for later release)
can only be measured in terms of normally-pigmented plaice larvae
having a reasonable chance of survival after metamorphosis, the
causes and cures of pigment deficiency are matters of great practical
interest, and further experiments are planned to widen our understanding of the condition. Dannevig and Hansen (1962) observed that
when pigment-deficient young plaice were transferred to a large marine
Pond with normal daylight conditions, no pigment change occurred
Over a period of several months, but Mr. A. B. Bowers of the Marine
Biological Station, Port Erin, has recently demonstrated the reversib i b of pigment lack. In June 1962 a newly-metrtmorphosed plsice
with grossly deficient pigment was transferred to a small etatic tank
containing something less than 1 1. of frequently renewed sea water.
During the following 6 months, pigment slowly developed from dorsal
loci to produce the fully pigmented condition (personal communication).
69
population density is probably linked with a second relationship given
in Fig. 24, showing that smaller survivors among a stock usually have
less pigment cover than their larger contemporaries. It has already
been demonstrated that densely populated tanks 8r6 biased in favour
of smaller larvae (Figs. 19 and 20). With the exception of tank 1,
1960 (ringed in Fig. 23), all tanks were of equal size and egg stocking
rate. Figure 23 therefore incidentally compares mean d o d pigment
cover with the degree of survival in each tank. Heavier pigmentation
among less-dense tank populations could equally well be explained by
the differential mortality of imperfectly pigmented runts. Experiments
in 1962 also suggest some relationship between the degree of pigmentation at metamorphosis, and the temperature rbgime during incubation
and larval development. Food abundance might also be important
(J. D. Riley, personal communication).
It looks as if chromatophore development during organogeny is a
particularly sensitive and delicate process, easily disrupted by an
unfavourable environment. Heuts (1963) made this point with reference
to the regressive evolution of Cuecobarbus geertsii Boulenger, the blind
cave fish of the Congo. Norman (1934) and Follet (1954), on the other
hand, related the piebald condition in flatfish to vertebral damage,
whilst von Ubisch (1962) considered light intensity to be important.
The tank environment, involving surface contact and " community "
conditions, is completely foreign to the pelagic plaice larva, and it
says a great deal for the innate adaptability of the species, that high
survivals to metamorphosis can be achieved, even though abnormalities
commonly occur.
Since effective hatchery production (if intended for later release)
can only be measured in terms of normally-pigmented plaice larvae
having a reasonable chance of survival after metamorphosis, the
causes and cures of pigment deficiency are matters of great practical
interest, and further experiments are planned to widen our understanding of the condition. Dannevig and Hansen (1962) observed that
when pigment-deficient young plaice were transferred to a large marine
Pond with normal daylight conditions, no pigment change occurred
Over a period of several months, but Mr. A. B. Bowers of the Marine
Biological Station, Port Erin, has recently demonstrated the reversib i b of pigment lack. In June 1962 a newly-metrtmorphosed plsice
with grossly deficient pigment was transferred to a small etatic tank
containing something less than 1 1. of frequently renewed sea water.
During the following 6 months, pigment slowly developed from dorsal
loci to produce the fully pigmented condition (personal communication).