K. GOPINATH
123
of the material from its healthy reddish tint to a
dull brown. At the same time, the presence of
numerous minute parasites on the shrimp meat
becomes visible even to the naked eye as minute
whitish moving specks. This attack by the
parasite is followed by the formation of a
very pungent odour which renders the infected
material a highly objectionable article of food.
The spoilage once started goes on with extreme
rapidity destroying the material in no time.
Most of the meat is converted into a brown powdery
substance which collects at the bottom of the
container. Deposits of this powder ranging from
one to one and a half centimeters thickness have
been observed in certain cases. In the unshelled
samples, only the shells remain after some time, the
meat having been converted into the powdery
residue. Another characteristic of this infection,
which is of much importance to the industry, is
the considerable reduction in weight brought
about on the cured material. It is estimated
after repeated trials in the laboratory that about
one third of the total weight of the cured material
is thus lost by this infection.
The real cause of this spoilage is found to be the
attack of mites, which on superficial examination
appear as white specks on the surface of the shrimp
meat. These mites belong to the group of
Cheese-mites, which have a wide range of distri-
bution. Members of this group are the simplest
and probably the smallest of mites and the name
Cheese-mites has been given to them because of
the frequency with which they attack commercial
cheese. The species involved in the spoilage of
shrimps is Caloglyphus micophagus (?)*
In attacking the shrimps, the mites eat into
the meat converting it into the brown powdery
substance. A thoroughly spoiled shrimp meat
has a typical 'worm eaten' appearance and is
unwholesome to smell and taste. The brown
powdery substance is composed of mite fæces,
dead mites, moulted skins and mite eggs in various
stages of development and is known to be defi-
nitely allergic producing itching and urticarious
swellings. It is probable that the strong pungent
odour characteristic of mite infested shrimp is
the result of some sort of secretion produced by the
mite, since it is positively known in the case of
ordinary cheese-mites that they saturate the cheese
with some kind of secretion before eating into it.
Although the possibility of gastro-intestinal
disturbances due to the consumption of mite
infested food stuffs is mentioned by Patton [1930]
no such instance has up till now been brought to
the notice of the author.
All the different stages in the life history of the
mite such as eggs, larvæ, nymphs and adults are
usually found on the infected shrimp meat. The
eggs are very minute, translucent and ovoid with
rounded ends and under ordinary conditions deve-
lop in the course of a couple of days. The larva
which is smaller and rounded in shape has only
three pairs of legs. The larva moults to form the
nymph, which in turn moults to form the adult,
the hypopal stage being absent in this. The
total period of development from the egg to
the adult is usually from four to seven days and
during this period it undergoes three main moults.
The period of development, however, shows ten-
dency to lengthen when there is not enough food
material for the organisms to thrive on. For
example, at the initial stage of the infection when
food material is plentiful and conditions most
favourable, development proceeds with rapidity
and is completed in about four days. When
the greater part of the shrimp meat has deteriora-
ted by being converted into the powdery residue
the period of development is also lengthened from
four to seven days.
SOURCES OF INFECTION
Two main methods of infection are observed to
take place. (1) Direct infection by the parasites
themselves and (2) Infection through a trans-
mitting host, viz. the common house fly.
(1) In the course of experiments, when freshly
cured shrimps were kept in the vicinity of infected
samples, the mites were actually observed to crawl
from the latter to the former. Though the shrimps
were kept in petri dishes and covered over with
glass plates, the infection was found to take place.
By the fourth day after the shrimp meat was thus
kept, the mites were found to crawl on the outside
of the petri dishes and over the glass plates, while
a few of the smaller ones happened to get inside
the dishes. These began to multiply rapidly and
after a week a large number of eggs larvæ and
adults was found on the material.
Probably this method of infection is the one
that usually takes place during the storage of
shrimps in godowns. Old and fresh consignments
are generally stored in the same room, the holes
and crevices of which are infested with mites.
It is easy to see how infection of fresh consignments
is brought about. The cured shrimps are packed
in gunny bags or heaped at the corners of the rooms
and none of these methods affords sufficient
protection against the entry of so small an or-
ganism as the mite.
(2) A number of flies was caught from the
vicinity of the place of storage and when these
were examined under a microscope some of them
showed the presence of young mites, eggs and
*For classification and description, refer appendix I
at the end of this paper.