THE ARTXJ!'IOIAL PROPAOATION OF MARIXE FISH
2. Increased survivals in the control tanks of a 8 a h i t y experiment: 1061
Without a trustworthy rearing technique, long-term survival
experiments to test specific physico-chemioal variables am usually
unrewarding. Technioal shortcomings may mask the effect of the
special factor or factors under consideration. By 1961, our understanding of the way in which the hazards of a tank environment oan
operate against a developing plaice stock waa far from complete,
though we had learned how to avoid some of the more common
technical mistakes. This partial understanding was not enough to
guarantee an incontrovertible outcome to a 1961 experiment investigating the effect of salinity flux on the survival of plaice larvae in
tanke. Full details can be found in a recent paper by Shelbourne
(1963b). Although only partidly fulfilling its main aim, the experiment
constituted a technioal advance in two important respects. Firstly, it
demonstrated the usefulness of a new appwatue designed to maintain
a special chemical regime in conditions of constant flow. Secondly, it
showed that in certain circumstances, survival mtes and survivor
densities could be inoreased to three times the best result of former
years.
Apparatus. Salinity experiments on marine fish eggs and larvae
are usually conducted in static sea water adjusted to the desired
salinity with distilled water or salt preparations (Holliday and Blaxter,
1960). This arrangement may be satisfactory for a short time, but
static water conditions are not ideal for long-term experiments.
Bishai (1961) describes a constant-flow salinity apparatus which,
though giving good results for young plaice and larval lumpsuckers
(Cyclopterw, lumpus L.), was unsuitable for delicate larval herring.
The most direct, and certainly the least laborious way to ensure a
continuous flow of salinity-adjusted sea water for a long period of
time, would be to operate an automatic control salinometer in an
overhead mixing chamber, and to run the adjusted product into
experimental tanks by gravity feed. This system was not availabIe
in 1961, so the following method was used (Figs. 12 and 13). A measured
amount of hatchery sea water of known salinity waa run through a
gless-wool filter each morning, into a leaohed asbestos-cement reservoir
of 460 1. capacity, and a calculated volume of dietilled or tap water
added to lower the salinity to ti pre-determined level. After thorough
mixing, the product was lifted by air-pump at a mte slightly in exam3
of incubator requirements, into a polythene header tank above the
mgemoir. This tank waa fitted with a delivery manifold emerging
a point near the bottom on the front face, and elso with an overflow pipe leading back to the mmrvoir. Water fell by gravity at an
49
2. Increased survivals in the control tanks of a 8 a h i t y experiment: 1061
Without a trustworthy rearing technique, long-term survival
experiments to test specific physico-chemioal variables am usually
unrewarding. Technioal shortcomings may mask the effect of the
special factor or factors under consideration. By 1961, our understanding of the way in which the hazards of a tank environment oan
operate against a developing plaice stock waa far from complete,
though we had learned how to avoid some of the more common
technical mistakes. This partial understanding was not enough to
guarantee an incontrovertible outcome to a 1961 experiment investigating the effect of salinity flux on the survival of plaice larvae in
tanke. Full details can be found in a recent paper by Shelbourne
(1963b). Although only partidly fulfilling its main aim, the experiment
constituted a technioal advance in two important respects. Firstly, it
demonstrated the usefulness of a new appwatue designed to maintain
a special chemical regime in conditions of constant flow. Secondly, it
showed that in certain circumstances, survival mtes and survivor
densities could be inoreased to three times the best result of former
years.
Apparatus. Salinity experiments on marine fish eggs and larvae
are usually conducted in static sea water adjusted to the desired
salinity with distilled water or salt preparations (Holliday and Blaxter,
1960). This arrangement may be satisfactory for a short time, but
static water conditions are not ideal for long-term experiments.
Bishai (1961) describes a constant-flow salinity apparatus which,
though giving good results for young plaice and larval lumpsuckers
(Cyclopterw, lumpus L.), was unsuitable for delicate larval herring.
The most direct, and certainly the least laborious way to ensure a
continuous flow of salinity-adjusted sea water for a long period of
time, would be to operate an automatic control salinometer in an
overhead mixing chamber, and to run the adjusted product into
experimental tanks by gravity feed. This system was not availabIe
in 1961, so the following method was used (Figs. 12 and 13). A measured
amount of hatchery sea water of known salinity waa run through a
gless-wool filter each morning, into a leaohed asbestos-cement reservoir
of 460 1. capacity, and a calculated volume of dietilled or tap water
added to lower the salinity to ti pre-determined level. After thorough
mixing, the product was lifted by air-pump at a mte slightly in exam3
of incubator requirements, into a polythene header tank above the
mgemoir. This tank waa fitted with a delivery manifold emerging
a point near the bottom on the front face, and elso with an overflow pipe leading back to the mmrvoir. Water fell by gravity at an
49