THE BREEDIN(: O F THE WORTH ATLANTIC FltESHW'ATEIE-EELS
161)
Tucker (1959a, p. 498) writes : " Means of 56-86 and 60.06 vertebrae
were obtained in batches of young from the same parents, a difference
proportionally similar to that pertaining between whole populations of
Atlantic Anguilla," he correctly refers to T~~ning's (1962, p. 15) observation on temperature shock-effect, but omits to give tho character of the
shock and the temperatures before and after the shock a t which the
eggs were reared.
T h i n g (1952, p. 15) gives the results of two experiments, one in
which the extreme variation of average values is 68.69 and 60.12
vertebrae or a difference of 1.43, and another in which it is between
56.86 and 60.06 vertebrae ; this latter is the one in the quotation from
Tucker above and is the very extreme example of ail Thing's
experiments.
T h i n g had two control samples, one reared a t 2.7"C averaging
58.38 vertebrae and one at 12°C averaging 59.36 vertebrae.
Now the great difference, cited by Tucker, of 3.20 vertebrae waa
only obtained in a very special way. The batch with 66.86 vertebrae
was first reared at 2.4"C until the sensitive period, then exposed to a
shock treatment of 20 day-degrees, or about 30 hr, a t 16OC, and then
again reared at 2-4°C. The other batch averaging 60.06 vertebrae was
first reared a t 12"C, then in the sensitive period exposed to 20 daydegrees, or about 177 hr, at, 2.7'6. In short, the extreme result was only
obtained if the eggs were reared a t a certain low temperature, then in
the sensitive period suddenly exposed to a quite different, very high
temperature in a rather short time, after which the eggs were moved
back to the original low temperature. These are conditions which
cannot possibly be similar in any way to temperatures influencing the
eel eggs during their development.
Here I would like to cite Schmidt (1929, p. 16) : " The larvae recently
emerged from the ova (praelarvae and quite young larvae) are extremely
fragile, so much so that the majority undoubtedly perish in the nets
even under the most favourable weather conditions, and our hauls
therefore are not likely to present a true picture of the quantitative
proportions between praelarvae and the somewhat larger larvae. Of the
European eel, we have comparatively many praelarvae and quite young
larvae, in which the oil globule of the yolk sac has not yet been resorbed. These are found somewhat deeper down than rather older
larvae, but still in what may relatively be called surface strata, abt.
200-500 metres down."
This means that the number of myomeres in the larvae are so well
developed that they can be counted and thus a distinction be made
between A . anguilla and A . rostrata larvae ; and furthermore that we
161)
Tucker (1959a, p. 498) writes : " Means of 56-86 and 60.06 vertebrae
were obtained in batches of young from the same parents, a difference
proportionally similar to that pertaining between whole populations of
Atlantic Anguilla," he correctly refers to T~~ning's (1962, p. 15) observation on temperature shock-effect, but omits to give tho character of the
shock and the temperatures before and after the shock a t which the
eggs were reared.
T h i n g (1952, p. 15) gives the results of two experiments, one in
which the extreme variation of average values is 68.69 and 60.12
vertebrae or a difference of 1.43, and another in which it is between
56.86 and 60.06 vertebrae ; this latter is the one in the quotation from
Tucker above and is the very extreme example of ail Thing's
experiments.
T h i n g had two control samples, one reared a t 2.7"C averaging
58.38 vertebrae and one at 12°C averaging 59.36 vertebrae.
Now the great difference, cited by Tucker, of 3.20 vertebrae waa
only obtained in a very special way. The batch with 66.86 vertebrae
was first reared at 2.4"C until the sensitive period, then exposed to a
shock treatment of 20 day-degrees, or about 30 hr, a t 16OC, and then
again reared at 2-4°C. The other batch averaging 60.06 vertebrae was
first reared a t 12"C, then in the sensitive period exposed to 20 daydegrees, or about 177 hr, at, 2.7'6. In short, the extreme result was only
obtained if the eggs were reared a t a certain low temperature, then in
the sensitive period suddenly exposed to a quite different, very high
temperature in a rather short time, after which the eggs were moved
back to the original low temperature. These are conditions which
cannot possibly be similar in any way to temperatures influencing the
eel eggs during their development.
Here I would like to cite Schmidt (1929, p. 16) : " The larvae recently
emerged from the ova (praelarvae and quite young larvae) are extremely
fragile, so much so that the majority undoubtedly perish in the nets
even under the most favourable weather conditions, and our hauls
therefore are not likely to present a true picture of the quantitative
proportions between praelarvae and the somewhat larger larvae. Of the
European eel, we have comparatively many praelarvae and quite young
larvae, in which the oil globule of the yolk sac has not yet been resorbed. These are found somewhat deeper down than rather older
larvae, but still in what may relatively be called surface strata, abt.
200-500 metres down."
This means that the number of myomeres in the larvae are so well
developed that they can be counted and thus a distinction be made
between A . anguilla and A . rostrata larvae ; and furthermore that we