Eye Stalk Ablation in Crustaceans describe in simple language and easy to understand

1. Eye stalk ablation in
crustaceans
KARTICKAY CHAWLA
B.F.SC. 3RD YEAR
5TH SEMESTER

3. Introduction
 Shrimp, prawn and crab brood stock are collected either from the culture ponds
or natural water bodies.
 The brooders may be at different stages of maturity and usually either matured
or berried or ready to spawn brooders are preferred for the hatchery seed
production.
 However, some times the brooders may be in their early maturing or late
maturing stages that may require some more time for the release of their
gametes.
 Under such circumstances, the speeding of maturity is necessary to make them
spawn.
 Therefore their maturity is induced through biological interference in
crustaceans.

4.  There are many inducement methods, some may be external and some may be
internal.
 Some species like freshwater prawns respond well to the feed given and may
mature fast if right feed is given at right quantity.
 In penaeids, the maturation is well controlled by hormones and therefore
the manipulations are required at their hormone production sites to make
them mature and breed.
 This applies to crabs too.

7. Eye stalk ablation
 It was earlier understood that the endocrine glad present in the eyestalk of
the crustaceans is responsible for the blocking of certain activities
connected with the gonadal maturation.
 It has been named as X organ sinus glad and sinus complex, that secretes
Moulting Inhibiting Hormone (MIH).
 It is also termed as Growth Inhibiting Hormone (GIH) since it inhibits
growth in general.
 Therefore removal or blocking of this hormone from its activity is believed
to help in the speedy maturation of the animals.

8.  Panouse (1943) observed that removal of eyestalk of shrimp Palaemon
serratus led to ovarian development.
 Ever since this discovery several workers have tried to induce gonadal
maturation in prawn through ablation of eyestalk and also the breeding of
different crustacean.

9. Eye stalk ablation and its role in
gonadal development
Introduction :
 Shrimp seeds were collected from natural wild waters in the past.
 Following the development of hatchery technology and larval production in
captivity, seeds have been produced in the hatcheries and supplied to the
farms.
 However, there has been a difficulty in getting the mother shrimps for the
seed production.
 Matured mother shrimps have been collected from wild waters for copious
seeds and production of good quality seeds.

11.  It is a fact that all species of shrimps do not attain sexual maturity in confined
waters.
 It has been found that hormones secreted by the X-organ sinus gland complex
are responsible for the inhibition of the gonad maturation and breeding.
 Therefore, removal of eyestalk in the matured shrimps is believed to result in
the inducement for the maturation and spawning.
 Ablation or removal of the eyestalk for induction of maturation in crustacean is
an approved practice in the crustacean seed production as an essential
prerequisite for the maturation of the shrimps in captivity.
 In female penaeid shrimp and female crabs the eyestalk has the gland (a
complex) for the production and storage of the gonad inhibiting hormone (GIH)
that inhibits the maturation of the ovary.

12. Eye stalk ablation
 It is the removal or extirpation or elimination of one or both eyestalks in
order to at least reduce the level of inhibitory hormone or to fully prevent
their secretion in the body for full and accelerated maturation of the
ovaries.
 The eye stalk ablation can be either unilateral or bilateral ablation based on
the removal of single or both eye stalks.
 If both eye stalks are removed, then it is called as bilateral eye stalk
ablation.

13. Background of eye stalk ablation
 The stimulating effect of eyestalk ablation on reproduction of decapod
crustacean was first evaluated for Penaeid culture in the early 1970’s when
French researchers attempted bilateral eyestalk ablation (both eyes).
 Ablated females suffered high mortality (Probably due to hormone non-
synchronization) and ova were typically reabsorbed with out subsequent
spawning.
 These problems were alleviated by the ablation of only one eye stalk (unilateral
eyestalk ablation) which provided moderate hormonal stimulus without re-
absorption of ova or excessive mortality.
 Consequently, unilateral eyestalk ablation rapidly emerged worldwide as a simple
procedure for inducing reproduction of numerous species of Penaeid shrimp
reared in captivity.

14. The ablation process
 It is more essential to perform the ablation at appropriate stage in order to
avoid loss of mother shrimps.
 For all practical reasons, it is emphasized that only inter molt shrimp is to be
used for ablation.
 Post-molt (stage) female shrimps are not recommended for ablation, due to
increased risk of handling mortality associated with softened exoskeleton and
weakness of the animal Pre-molt (Stage IV) individuals are also not recommended
since there may be immediate molting during recovery from the ablation process
leading to loss or delay in spawning.
 It was observed that ablation under taken between 8-20 days post-molt resulted
in significantly greater egg production than that of ablation at 13-15 days post-
molt indicating the inter moult period is the best one for the ablation process.

15. Methods of eyestalk ablation:
 Several methods are available for the removal of eyestalk. They are,
 (i) Cutting the eye stalk near the base with a pair of scissors followed by
sealing with a pencil type soldering iron. This method is called
electrocautrization.
 (ii) Pinching of eyestalk and squeezing of eye ball contents out
 (iii) Incision of eyeball followed by eunucleation of contents.

16.  Enucleation, cauterization and ligation are the methods that have been effective
in removing (or) destroying the X organ / sinus gland complex. Never the less,
the stress that will be arising due to the ablation has its own ill effects on the
animals.
 Stress can be reduced and losses minimized if shrimps are held in chilled water
before and after ablation.
 To minimize stress, the ablation should be performed as quickly as possible under
chilled water.
 Further the stress to the mother shrimps can be reduced by doing the ablation
in the early morning hours, when the temperatures is the lowest.
 Care should be taken to see that female mortality due to ablation is very low.

17. a) Enucleation
 Grasp the eyestalk just behind the eyeball using the thump and index finger.
 Squeeze hard and roll the thump and finger outwards away from the body,
thus crushing the eyestalk and squeezing out the contents of the eye.
 The objective is to squeeze the contents outwards and not let them follow
the eyestalk back in to the head region.
 Enucleation has the advantages of simplicity and rapid clotting of hemolymph
within the empty eyestalk.

18. b) Ligation
 A string is tied around the base of the eyestalk as close to the carapace as
possible.
 The string should be drawn fairly tight causing the eyestalk to fall off in a
few days.
 The procedure does not leave the shrimp with open wound.
 However, successful ablation is often unpredictable and this process will give
the result only after two or three days.

19. c) Cautery: (Electrocauterisation)
 This method is the severing eyestalk followed by sealing of the wound
through the process called electrocauterization.
 Heated forceps, or the application of a silver nitrate bar on the wound will
prevent the secondary infection at the wound site.
 Ø Pinching method of ablation required one person and it is without
application of antibiotics.
 Ø Ligation requires two persons, one to hold the shrimp and the other to tie
the eyestalk.
 Ø Cautery requires either a cautrizer (or) silver nitrate bar.

20. Effects of eye stalk ablation
 The effects of eyestalk ablation vary with season and stage in the molt
cycle.
 Ablation is performed on either left or right compound eyestalk.
 The damaged eye should be ablated in order to leave the shrimp with one
unablated functional eye.

21. Fecundity and possibilities for spawning:
 Ovarian development in sexually matured female can commence within 3 days
of ablation, followed by a first spawn within one week.
 If ablated during the inter molt stage, the females will mature and spawn
immediately.
 If ablated during early molt, they will molt before maturing. There have
been varied observations and results due to ablation.

22.  - The fecundity and viability of larvae that are obtained from abated females
are observed to be inferior to larvae from females matured in the wild indicating
the superiority of the larvae from the natural spawning.
 - In the captive maturation there might be poor or low embryonic development
that may influence juvenile’s survival and growth.
 - If the females are smaller, there will be higher lipid in the body and variations
in the distribution of yolk among oocytes. These were identified from the crab
(Paratelphusa hydrodromus) during the pre-spawning.
 - Those differences presumably are consequences of hormonal imbalances due to
ablation. They are physiological (or) embryological limitation such as improper
oocyte differentiation, nutrient storage food supply (or) temperature.

23. Role of eyestalk in the reproduction
of crustaceans
 In prawns, the neutrosecretory centers located in the ganglia of eyestalk (X
organ sinus gland complex), brain and thoracic ganglia mainly influence the
egg production (vitellogenesis).
 While the X organ sinus gland complex of the eyestalk inhibits vitellogenesis
under the influence of its hormone, viz., Gonad Inhibiting Hormone (GIH),
the brain and thoracic ganglia promote vitellogenesis by their hormone, viz.,
Gonad Stimulating Hormone (GSH).

24.  Under natural conditions, when the physiological parameters of the prawns and the
environmental factors are favorable, the GSH promotes vitellogenesis.
 On the basis of this principle, the ovarian development and maturation of gonads are
obtained in prawns through the unilateral eyestalk ablation (removal of one of the eyestalk).
 It is also worth mentioning here, that the removal of both the eyestalks though lead to
rapid ovarian growth, spawning does not result due to physiological stress.
 It has been observed that the ova are reabsorbed in the ovary.
 The eye stalks apart from GIH, produce other neutrosecretory hormones which regulate
lipid metabolism and protein synthesis in hepatopancreas; induce hyperglycemia in blood to
combat stress; regulate calcium metabolism during cuticle formation; effect water balance
during moulting; inhibit production of moulting hormone by ‘Y’ organ and influence movement
of pigments in chromatophores.

25.  - Removal of both eyestalk is called as bilateral eye stalk ablation.
 - The behavioral pattern of the eye stalk ablated females especially their
feeding and matting are also not affected.

26. Points in eyestalk ablation in crustaceans:
 1. For the procurement of broodstock of crustaceans for inducement, some of
the shrimps / prawns / crabs are reared in ponds to harvestable size and later
they may be allowed to grow for further period of one year before subjecting
them for eyestalk ablation.
 2. The eyestalk ablation is carried out only in female and not in male.
 3. For eyestalk ablation, P. indicus with a carapace length of 30 mm (total length,
150 mm weight > 20 g) and P. monodon with the carapace length of 50-80 mm
(total length > 200mm and weight >100g) are normally selected.
 4. Before removing eyestalks, the brood stocks are kept in large plastic pools
containing filtered sea water of 33 ± 20%.

27.  5. After about 24 hrs, the eyestalks are removed in the females using
electrocauterization technique.
 6. The ablated female and unablated males are then kept at 2:1 in larger
circular plastic lined pools, in which the sea water is made to circulate
through sub-gravel filter by air lifts.
 7. The breeders are fed ad libitum using chopped fish or calm meat.
 8. The temperature, salinity and pH of the medium are maintained at 28 ± 2,
32 ± 2% and 8-8.2 respectively.

28.  Generally the mating and impregnation are ensured in the shrimps if the
males and females are kept separately in two tanks and the females are
introduced into the male tank when they are about to molt.
 The separation of sexes seems to enhance the attraction between them and
facilities early spawning.

30. Methods of eye stalk ablation
 Eye stalk ablation can be done in two types.
 They are, unilateral ablation and bilateral ablation.
 In unilateral ablation, only one eye will be removed and the animal will be
allowed to live one eye, while in bilateral ablation method, both the eyes will
be removed with the stalks of the eye.
 Although the bilateral ablation results in faster maturation and yielding
desirable results, there are some demerits in this method.

31. References
 Pillay.T.V.R., Thomas.P. (2003), BREEDING AND SEED PRODUCTION OF FINFISH &
SHELL FISH, Daya Publishing House, Delhi. pp 258-263.
 Summer Inst. on breeding and rearing of marine prawns. CMFRI,Cochin.
 Shrimp and prawn farming in the Western Hemisphere. Dowden Hutchinson &
Ross Inc.(Ed. Joe. A.Hanson and Harold L.Goodwin)
 A manual for operating a small Scale recirculation freshwater prawn hatchery.
BOBP/ Mag/ 13 (Author: R.Chowdhury).