284
THE BIOLOGY OF EUPHAUSIIDS
amount of information about the life history of an animal can be
obtained if this type of sample analysis is done a t intervals throughout
a year and simultaneous observations made on the degree of sexual
maturity of the individuals of different sizes within the population.
The growth rates of several species of adolescent and adult
euphausiids have been investigated (Table XXVIII). I n studying
growth, one of the major problems is to decide what or which parameters
of the animal’s body to use-weight, volume, total body length, or the
length or lengths of one or several parts of the body. The extremities
of the body, such as the antennae, telson, and uropods are often
damaged in the process of catching the animals and so measurements
inclusive of these parts are subject to error. It has become customary
to adopt a measurement of carapace length for estimating growth of
shrimp-like organisms but not all authors use this parameter. Even
those who do, make different measurements of the carapace; some
measure the length of the dorsal median line from the anterior tip of
the rostrum to the posterior end of the carapace but in species such a9
Thysanoessa raschii the rostrum is often bent or damaged. Mauchline
(1958~) designed a modified screw micrometer with which quick and
accurate measurements can be made of the distance between the
posterior face of the eye notch and the posterior dorsal median end of
the carapace. This is an awkward measurement to make by any other
means but has certain advantages. The eye notch and the posterior
median end of the carapace are well-defined morphological features not
subject to damage. Examples of other parameters of body length which
have been used are:
Tip of rostrum to end of telson (Praser, 1936; Einarsson, 1945;
Anterior margin of the eyes to end of telson (Bargmann, 1945;
Anterior end of carapace to posterior end of sixth abdominal
Centre of eye to posterior end of sixth abdominal segment (Ruud,
Basically it does not matter which measurement is used as an index
of growth as long as its relationship to total length is stated. Ruud
(1936) states that his measurement, the distance between the centre of
the eye and the end of the sixth abdominal segment, must be multiplied
by 1.2 in Neganyctiphanes norvegica to be converted to a measurement
of total length which he defines as the distance between the tip of the
rostrum and the posterior end of the telson. Mauchline (1960) examined
Nemoto, 1957; Wiborg, 1966).
Baker, 1959).
segment (Dunbar, 1940).
1936).
THE BIOLOGY OF EUPHAUSIIDS
amount of information about the life history of an animal can be
obtained if this type of sample analysis is done a t intervals throughout
a year and simultaneous observations made on the degree of sexual
maturity of the individuals of different sizes within the population.
The growth rates of several species of adolescent and adult
euphausiids have been investigated (Table XXVIII). I n studying
growth, one of the major problems is to decide what or which parameters
of the animal’s body to use-weight, volume, total body length, or the
length or lengths of one or several parts of the body. The extremities
of the body, such as the antennae, telson, and uropods are often
damaged in the process of catching the animals and so measurements
inclusive of these parts are subject to error. It has become customary
to adopt a measurement of carapace length for estimating growth of
shrimp-like organisms but not all authors use this parameter. Even
those who do, make different measurements of the carapace; some
measure the length of the dorsal median line from the anterior tip of
the rostrum to the posterior end of the carapace but in species such a9
Thysanoessa raschii the rostrum is often bent or damaged. Mauchline
(1958~) designed a modified screw micrometer with which quick and
accurate measurements can be made of the distance between the
posterior face of the eye notch and the posterior dorsal median end of
the carapace. This is an awkward measurement to make by any other
means but has certain advantages. The eye notch and the posterior
median end of the carapace are well-defined morphological features not
subject to damage. Examples of other parameters of body length which
have been used are:
Tip of rostrum to end of telson (Praser, 1936; Einarsson, 1945;
Anterior margin of the eyes to end of telson (Bargmann, 1945;
Anterior end of carapace to posterior end of sixth abdominal
Centre of eye to posterior end of sixth abdominal segment (Ruud,
Basically it does not matter which measurement is used as an index
of growth as long as its relationship to total length is stated. Ruud
(1936) states that his measurement, the distance between the centre of
the eye and the end of the sixth abdominal segment, must be multiplied
by 1.2 in Neganyctiphanes norvegica to be converted to a measurement
of total length which he defines as the distance between the tip of the
rostrum and the posterior end of the telson. Mauchline (1960) examined
Nemoto, 1957; Wiborg, 1966).
Baker, 1959).
segment (Dunbar, 1940).
1936).