Bu içeriği görüntülemek için JoVE aboneliği gereklidir. Oturum açın veya ücretsiz deneme sürümünü başlatın.
Method Article
Anestezi uygulanan dişi yengeçler üzerinde iki göz konuşması ablasyon protokolü (yani koterizasyon ve cerrahi yaklaşımlar) uygulandı. Çamur yengeçlerinin göz konuşması ablasyonu, hayatta kalma oranını düşürmeden yumurtalıkların olgunlaşmasını hızlandırdı.
Çamur yengeçleri (Scylla spp.), Hint-Batı Pasifik bölgesinde bulunabilen ticari olarak önemli kabuklu türleridir. Kültür sırasında, yumurtalık olgunlaşmasının indüksiyonu, olgun çamur yengeçlerine olan tüketici talebini karşılamak ve tohum üretimini hızlandırmak için önemlidir. Göz konuşması ablasyonu, çamur yengeçlerinde yumurtalık olgunlaşmasını arttırmak için etkili bir araçtır. Bununla birlikte, çamur yengeçlerinin göz konuşması ablasyonu için standart bir protokol yoktur. Bu çalışmada, iki göz konuşması ablasyon tekniği tanımlanmıştır: koterizasyon (anestezi uygulanmış bir yengecin göz konuşmasını ablate etmek için sıcak metal kullanımı) ve cerrahi (cerrahi makas kullanılarak göz konuşmasının çıkarılması). Göz konuşması ablasyonundan önce, cinsel olarak olgun dişiler (CW > 86 mm), deniz suyu ile bir buz torbası (-20 ° C) kullanılarak uyuşturuldu. Su sıcaklığı 4 ° C'ye ulaştığında, buz torbası sudan çıkarıldı. Akan deniz suyu (ortam sıcaklığı: 28 °C), göz sapı ablasyonundan hemen sonra anesteziden kurtulmak için kullanıldı. Mortalite, göz konuşması ablasyonu işlemi sırasında veya sonrasında ortaya çıkmadı. Burada sunulan göz konuşması ablasyon protokolü, çamur yengeçlerinin yumurtalık olgunlaşmasını hızlandırdı.
Scylla cinsine ait dört çamur yengeç türünün tümü, su ürünleri yetiştiriciliğinde ticari açıdan önemli kabuklu türleridir 1,2. Çamur yengeçleri de dahil olmak üzere kabukluların büyümesi ve bunların pre-olgun (alt yetişkin veya ergen) fazdan cinsel olarak olgun (yetişkin) faza dönüşümü, yaşlı ve daha küçük dış iskeletlerin periyodik olarak dökülmesini içeren bir kalıplama işlemi ile gerçekleşir. Carapace genişliği (CW), şelayedler ve abdominal flep morfolojileri, Scylla spp'nin cinsel olgunluğunu belirlemek için yaygın olarak kullanılmaktadır. 3,4,5. Kalıplama işlemi çeşitli hormonların etkisiyle düzenlenir ve çok miktarda enerji gerektirir6. Normal kalıplama işlemine ek olarak, gönüllü olarak veya dış faktörler tarafından indüklenen uzuvların kaybı, hayatta kalma oranlarını etkilemeden yengeçlerin erimesini hızlandırır 7,8,9. Bu nedenle, uzuv ototomisi, yumuşak kabuklu çamur yengeç yetiştiriciliği endüstrisinde erime indüksiyonu için yaygın olarak kullanılmaktadır 7,9.
Tek taraflı veya iki taraflı göz konuşması ablasyonu çoğunlukla gonad olgunlaşması ve tohum üretimi için tatlı su karidesi ve deniz karidesinde popülerdir10,11,12,13. Kabuklularda yaygın göz konuşması ablasyon teknikleri şunları içerir: (i)14,15 ipi kullanarak göz konuşmasının tabanında ligasyon; (ii) sıcak forseps veya elektrokoter cihazları kullanılarak göz konuşmasının koterizasyonu16; (iii) açık bir yara bırakmak için göz konuşmasının çıkarılması veya doğrudan sıkıştırılması12; ve (iv) gözün distal kısmını jiletle kestikten sonra kesi yoluyla göz konuşması içeriğinin çıkarılması17. Göz sapı X-organları, kabukluların hiperglisemik hormonlarını (CHH), molt inhibe edici hormonları (MIH) ve vitellogenezi inhibe eden hormonları (VIH) düzenledikleri için kabuklularda önemli endokrin organlardır 6,18,19,20,21,22. Göz konuşması X-organları (veya sinüs bezi kompleksi), nöropeptit hormon ailesi6'ya ait vitellogenezi inhibe eden hormonlar (VIH) olarak da bilinen gonad inhibe edici hormonları (GIH) sentezler ve serbest bırakır. Tek taraflı veya iki taraflı göz konuşması ablasyonu, GIH sentezini azaltır, bu da uyarıcı hormonların (yani, gonad uyarıcı hormonlar, GSH) baskınlığına ve kabuklularda yumurtalık olgunlaşma sürecinin hızlanmasına neden olur23,24,25,26. Göz konuşması ablasyonundan sonra GYH'nin etkisi olmadan, dişi kabuklular enerjilerini yumurtalık gelişimine adamışlardır27. Tek taraflı göz konuşması ablasyonunun, kabuklularda yumurtalık olgunlaşmasının indüksiyonu için yeterli olduğu bulunmuştur11 ve karides ve yengeçlerin ablatlı göz konuşmasının birkaç kalıplamadan sonra yenilenebileceği bulunmuştur28. Scylla spp.'de kaydedilen dört yumurtalık gelişim aşaması vardır: i) olgunlaşmamış (evre-1), ii) erken olgunlaşma (evre-2), iii) olgunlaşma öncesi (evre-3) ve iv) tamamen olgun (evre-4)29,30. Olgunlaşmamış yumurtalık evresi olgunlaşmamış kadınlarda bulunur. Pubertal erime ve çiftleşmeden sonra, olgunlaşmamış yumurtalık gelişmeye başlar ve nihayet yumurtlamadan önce olgunlaşır (aşama-4)31.
Bir göz sapı ablasyon protokolü, çamur yengeç yavrularının gelişimi ve tohum üretimi için gereklidir. Küresel gıda pazarında, daha yüksek kas içeriğine sahip yengeçler yerine tam olgun yumurtalıklara (evre-4) sahip olgun çamur yengeçleri tüketiciler tarafından tercih edilmektedir ve bu nedenle büyük erkeklerden bile daha yüksek bir ticari değere sahiptir. Çamur yengeçlerinin göz konuşması ablasyonu için tam bir protokol yoktur. Bu çalışmadaki göz konuşması ablasyon protokolü, tamamen anestezi uygulanmış yengeçler kullanarak stresi en aza indirir ve yengeç ısırıklarından personelin fiziksel yaralanmasını en aza indirir. Bu protokol kolay ve uygun maliyetlidir. Burada, gonadın olgunlaşmasını tetikleyebilecek Scylla spp.'nin göz konuşması ablasyonu için bir protokol sunuyoruz. İki göz konuşması ablasyon tekniği (koterizasyon ve cerrahi) test edildi ve dişi çamur yengeçlerinin gonadal gelişim hızına göre etkinlikleri karşılaştırıldı.
Bu protokol, Malezya Laboratuvar Hayvanları Bilimi Derneği tarafından özetlenen Bilimsel Amaçlar için Hayvanların Bakımı ve Kullanımı için Malezya Uygulama Kurallarına uygundur. Deneysel örneklerin kurban edilmesi, Ulusal Sağlık Enstitüleri Laboratuvar Hayvanlarının Bakımı ve Kullanımı Kılavuzu'na göre yapılmıştır (NIH Yayınları No. 8023, gözden geçirilmiş 1978). Cinsel olarak olgunlaşmamış dişi çamur yengeçleri (turuncu çamur yengeci S. olivacea), Malezya'daki Setiu Sulak Alanları'ndaki yerel pazardan (5 ° 66 ′ 62 ′ ′ N, 102 ° 72 ′ 33 ′ ′ E) toplandı. Çamur yengeç türleri morfolojik özelliklere göre tanımlanmıştır1.
1. Numune toplama ve dezenfeksiyon
Şekil 1: Cinsel olgunlaşma aşamalarını tanımlamak için kullanılan dişi çamur yengeçlerinin karın morfolojisi. Bu şeklin daha büyük bir versiyonunu görmek için lütfen buraya tıklayın.
2. İklimlendirme
3. Cinsel olgunluk için indüklenmiş kalıplama
4. Anestezi
5. Göz konuşması ablasyonu
6. Anestezi sonrası bakım
7. Yumurtalık olgunlaşmasının gözlenmesi
Gonad olgunlaşması
Diseke edilen dişilerin %100'ünde (n=6) göz konuşması ablasyonu yapılmadan önce kremsi beyaz over dokuları (olgunlaşmamış yumurtalıklar, evre-1) bulundu (Şekil 2). Göz sapı ablatlı dişi yengeçlerin gonad olgunlaşma oranı (n = 63; koterizasyon tekniği ile 31 dişi ve cerrahi teknik ile 32 dişi), 30 günlük bireysel yetiştirmeden sonra göz sapı ablasyonuna (n = 31) tabi tutulmayan dişi yengeçlere göre daha yüksekti (
Bu protokol, çamur yengeci Scylla spp.'nin göz konuşması ablasyonu için geliştirilmiştir ve gonad olgunlaşmasını indüklemek için etkili bir yöntem olarak uygulanabilir. Bu protokol, çamur yengeçlerinin ticari yumurtalık olgunlaşması için kolayca çoğaltılabilir ve çamur yengeç tohumu üretiminde gizli süreyi (bir yumurtlamadan diğerine geçen süre) azaltmak için uygulanabilir.
Kabukluların (yani, tatlı su karidesi, deniz karidesi) göz konuşması ablasyon...
Yazarların hiçbirinde çıkar çatışması yoktur.
Bu çalışma, Malezya Eğitim Bakanlığı tarafından, Malezya Terengganu Üniversitesi Tropikal Su Ürünleri Yetiştiriciliği ve Balıkçılık Enstitüsü'ne akredite edilmiş Yüksek Kurum Mükemmeliyet Merkezi (HICoE) programı kapsamında Malezya Eğitim Bakanlığı tarafından desteklenmiştir (Vot No. 63933 & Vot No. 56048). Universiti Malaysia Terengganu ve Sayap Jaya Sdn. Bhd.'nin Özel Ortaklık Araştırma Bursu (Vot. No. 55377) aracılığıyla desteğini kabul ediyoruz. Universiti Sains Malaysia'dan Khor Waiho ve Hanafiah Fazhan'a kadar ek bir Akademik Araştırmacı pozisyonu da kabul edilmektedir.
Name | Company | Catalog Number | Comments |
Aeration tube | Ming Yu Three | N/A | aquarium and pet shop |
Airstone | Ming Yu Three | N/A | aquarium and pet shop |
Autoclave machine | HIRAYAMA MANUFACTURING CORPORATION | N/A | MADE IN JAPAN |
Bleaching powder (Hi-Chlon 70%) | Nippon Soda Co.Ltd,Japan | N/A | N/A |
Blow torch | MR D.I.Y. Group Berhad | N/A | N/A |
Circular tank (32L) | BEST PLASTIC INDUSTRY SDN. BHD. | N/A | N/A |
Cotton hand gloves (thick) | MR D.I.Y. Group Berhad | N/A | N/A |
Cotton towel | MR D.I.Y. Group Berhad | N/A | N/A |
Digital thermometer | Hanna Instrument | HI9814 | Hanna Instruments GroLine Hydroponics Waterproof pH / EC / TDS / Temp. Portable Meter HI9814 |
Digital Vernier Caliper | INSIZE Co., Ltd. | N/A | |
Dissecting tray | Hatcheri AKUATROP | N/A | Research Center of Universiti Malaysia Terengganu |
Dropper bottle/Plastic Pipettes Dropper | Shopee Malaysia | N/A | N/A |
Ethanol 70% | Thermo Scientific Chemicals | 033361.M1 | Diluted to 70% using double distilled water |
Fiberglass tank (1 ton) | Hatcheri AKUATROP | N/A | Research Center of Universiti Malaysia Terengganu |
Fine sand | N/A | N/A | collected from Sea beach of Universiti Malaysia Terengganu |
First Aid Kits | Watsons Malaysia | N/A | N/A |
Flat head nickel steel metal rod (Screw driver) | MR D.I.Y. Group Berhad | N/A | N/A |
Formaldehyde | Thermo Scientific Chemicals | 119690010 | |
Gas cylinder (butane gas) for blow torch | MR D.I.Y. Group Berhad | N/A | N/A |
Gas lighter gun (long head) | MR D.I.Y. Group Berhad | N/A | N/A |
Glass beaker (100 mL)) | Corning Life Sciences | 1000-100 | |
Ice bag | Watsons Malaysia | N/A | N/A |
Perforated plastic baskets | Eco-Shop Marketing Sdn. Bhd. | N/A | N/A |
PVC pipe 15mm | Bina Plastic Industries Sdn Bhd (HQ) | N/A | N/A |
Refractometer | ATAGO CO.,LTD. | ||
Refrigerator | Sharp Corporation Japan | N/A | Chest Freezer SHARP 110L - SJC 118 |
Scoop net | MR D.I.Y. Group Berhad | N/A | |
Seawater | Hatcheri AKUATROP | N/A | Research Center of Universiti Malaysia Terengganu |
Siphoning pipe | MR D.I.Y. Group Berhad | N/A | N/A |
Spray bottle | Mr. DIY Sdn Bhd | N/A | N/A |
Stainless surgical forceps | N/A | N/A | N/A |
Stainless surgical scissors | N/A | N/A | N/A |
Submersible water pump | AS | N/A | model: Astro 4000 |
Tincture of iodine solution (Povidone Iodine) | Farmasi Fajr Sdn Bhd | N/A | N/A |
Tissue paper | N/A | N/A | |
Transparent plastic aquarium | Ming Yu Three | N/A | aquarium and pet shop |
Waterproof table | Hatcheri AKUATROP | N/A | Research Center of Universiti Malaysia Terengganu |
An erratum was issued for: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs. The Introduction, Protocol, Discussion and References were updated.
The forth sentence in the third paragraph of the Introduction has been updated from:
The eyestalk ablation protocol in this work minimizes stress by using fully sedated crabs and minimizes physical injury to personnel from crab bites.
to:
The eyestalk ablation protocol in this work minimizes stress by using fully anesthetized crabs and minimizes physical injury to personnel from crab bites.
The start of the Protocol has been updated from:
This protocol follows the Malaysian Code of Practice for the Care and Use of Animals for Scientific Purposes outlined by the Laboratory Animal Science Association of Malaysia. The sacrifice of the experimental samples was done according to the National Institutes of Health Guide for the Care and Use of Laboratory Animals (NIH Publications No. 8023, revised 1978). Sexually pre-mature female mud crabs (orange mud crab S. olivacea) were collected from the local market (5°66′62′′N, 102°72′33′′E) at the Setiu Wetlands in Malaysia. The mud crab species was identified based on morphological characteristics1.
to:
This protocol follows the Malaysian Code of Practice for the Care and Use of Animals for Scientific Purposes outlined by the Laboratory Animal Science Association of Malaysia and was approved by the Universiti Malaysia Terengganu's Research Ethics Committee (Animal ethics approval number: UMT/JKEPHMK/2023/96). The sacrifice of the experimental samples was done according to the AVMA Guidelines for the Euthanasia of Animals: 2020 Edition. Sexually pre-mature female mud crabs (orange mud crab Scylla olivacea) were collected from the local market (5°66′62′′N, 102°72′33′′E) at the Setiu Wetlands in Malaysia. The mud crab species was identified based on morphological characteristics1.
Section 4 of the Protocol has been updated from:
4. Cold-shock anesthesia
to:
4. Anesthesia
Section 5 of the Protocol has been updated from:
5. Eyestalk ablation
to:
5. Eyestalk ablation
Step 7.2.2 of the Protocol has been updated from:
Sedate the females individually with the cold shock anesthesia method.
to:
Anesthetize the females individually with the 2-PE immersion anesthesia method.
The Discussion has been updated from:
This protocol was developed for the eyestalk ablation of the mud crab, Scylla spp., and can be applied as an efficient method to induce gonad maturation. This protocol can be easily replicated for the commercial ovary maturation of mud crabs and can be implemented to reduce the latent period (time from one spawning to another) in mud crab seed production.
The eyestalk ablation of crustaceans (i.e., freshwater prawn, marine shrimp) is typically done to induce gonad maturation and out-of-season spawning11,12,13. Eyestalk ablation in brachyuran crabs has also been done to study molting25,32,33, hormonal regulation18, gonad maturation34, and induced breeding and reproductive performance35,36,37,38,39. Unilateral or bilateral eyestalk ablation influences the physiology of the crustacean. Eyestalk ablation following the protocol stated in this study also influences the ovarian maturation rate of mud crabs. In the control treatment (without eyestalk ablation), 43.33% ± 5.77% of female crabs had an immature ovary (stage-1). However, in the same rearing period (30 days), eyestalk-ablated female crabs had pre-maturing ovaries (stage-3; 56.67% ± 11.55% and 53.33% ± 15.28% with the cauterization and surgery techniques, respectively), which shows that eyestalk ablation can increase the gonad maturation of mud crabs. Previous studies have also reported that the ovarian development of intact crabs (without eyestalk ablation) is slower than that of eyestalk-ablated crabs25,31. Due to the slower gonadal development in intact crustaceans, eyestalk ablation is widely done in commercial prawn and shrimp hatcheries. In this protocol, the eyestalk-ablated female crabs achieved higher percentages of ovarian maturation compared to the female crabs without the eyestalk ablation treatment (Figure 3).
The gonad maturation of the mud crab is regulated by hormones21,40,41. The eyestalk contains important endocrine glands (i.e., the X-organ-sinus gland complex) that play vital roles in the gonadal maturation process of mud crabs18,21. Unilateral eyestalk ablation, either by cauterization or surgery, damages one of the major endocrine glands that is involved in the synthesis and release of inhibiting hormones (e.g., VIH), thereby resulting in a higher level of gonad-stimulating hormones (i.e., VSH).
The ovarian maturation stages of Scylla spp. can be differentiated by observing the ovarian tissue coloration with the naked eye29,30,42. Translucent or creamy white ovarian tissues are indications of immature ovaries29,30,42,43. In this study, immature ovaries (stage-1) were still found in the group of female crabs without eyestalk ablation due to the slower ovarian maturation process. However, the crabs in the eyestalk-ablated groups (both by the cauterization and surgery techniques) mostly showed pre-maturing ovaries (stage-3), with some individuals exhibiting fully matured ovaries (stage-4). Therefore, the protocol of eyestalk ablation described here can be used to increase ovarian maturation in female mud crabs. This protocol can also be applied directly to wild-collected mature female mud crabs to hasten their seed production. To evaluate the effectiveness of cauterization and surgery methods on mud crab gonad maturation and to ensure the accurate estimation of molting duration, sexually pre-mature crabs were used. After the (induced) molting of sexually pre-mature female crabs, we noticed that their ovaries were still in the immature or early developing stages29,44. After 30 days of rearing the newly mature female crabs (either eyestalk-ablated or without eyestalk ablation), the ovarian development stages (stage-1 to stage-4) were determined by the color of the ovarian tissues. This protocol encourages the use of the cauterization technique to perform eyestalk ablation in mud crabs to avoid any hemolymph loss and prevent infection at the ablated sites. Cauterization immediately seals the wound, whereas the surgery technique requires an additional step of disinfection using iodine. For commercial purposes, larger mature crabs, preferably at a later stage of ovarian maturation, should be selected for eyestalk ablation to shorten the time to reach the fully matured ovary stage for subsequent commerce or brood stock culture. In addition to eyestalk ablation, individual rearing with sand substrate and sufficient feeding, preferably with live feed, can increase the gonad maturation rate of mud crabs in captivity30,35,45,46.
Crustacean blood is called hemolymph and can be lost during eyestalk ablation. An excessive loss of hemolymph may lead to the death of eyestalk-ablated crabs, especially when performing surgery to remove the eyestalk. The hemolymph can coagulate in the wounded part to prevent loss. The application of a tincture of iodine can prevent infection of the wounded part. However, in comparison to the surgery technique, the cauterization technique seals the wounded part immediately, thereby preventing the loss of hemolymph and possible infection.
Mud crab mortality after unilateral eyestalk ablation with either cauterization or surgery was not found within the first 7 days. Thus, eyestalk ablation can be done with a higher survival rate. Unilateral eyestalk ablation does not hamper the survival rate of the crab33.
Stress during crab handling and eyestalk ablation may contribute to crab mortality. Proper anesthesia is needed to minimize handling stress during eyestalk ablation. In crustacean eyestalk ablation, chemical anesthetics (i.e., xylocaine, lidocaine) are used at the base of the eyestalk before eyestalk ablation14,15,17,47. However, due to the aggressive nature and large size of mud crabs, the use of anesthesia only at the base of the eyestalk is not sufficient and might result in additional stress to the animals during the injection. On the other hand, anesthesia by subjecting them to a lower water temperature is more economical and safer. The use of cold water for anesthesia in mud crabs is common and has been used in other studies due to its efficiency, simplicity, and minimal impact on recovery and survival37,48,49.
Although eyestalk ablation using both cauterization and surgery methods has a minimal effect on crab survival and enhances ovarian maturation, performing eyestalk ablation requires professional mastery of the techniques. The timing between the steps is critical as any delay between protocols adds additional stress for the crabs. Unlike the surgery technique, the cauterization technique is dangerous because it involves the use of flammable equipment (i.e., a blow torch and butane gas). Thus, extra caution is needed when performing the cauterization technique.
Crabs are cannibalistic in nature, and they are known to prey on others that have just completed their molt and are still in their soft-shell conditions7,50,51. Thus, rearing the crabs individually can avoid unnecessary mortality due to cannibalism. The use of individual rearing in mud crab culture is commonly practiced, both in high-density culture and pond culture, for fattening and soft-shell crab farming purposes8,52. This protocol also utilized individual rearing and maintenance. During the transportation of the crabs for rearing or commerce, the crab chelipeds are tied up securely (or even autotomized) to prevent fighting, unnecessary injury, and limb loss34.
The described protocol for eyestalk ablation should be performed with multiple persons. After completing the eyestalk ablation, non-disposable equipment (e.g., the aquarium, tray, towel, etc.) should be disinfected with 30 ppm chlorine. The crabs must be monitored at least twice per day. Any dead crabs, uneaten feed, ablated limbs, or molted crab shells should be swiftly disposed of (i.e., buried in soil with bleaching powder) to prevent any potential for disease spread.
to:
This protocol was developed for the eyestalk ablation of the mud crab, Scylla spp., and can be applied as an efficient method to induce gonad maturation. This protocol can be easily replicated for the commercial ovary maturation of mud crabs and can be implemented to reduce the latent period (time from one spawning to another) in mud crab seed production.
The eyestalk ablation of crustaceans (i.e., freshwater prawn, marine shrimp) is typically done to induce gonad maturation and out-of-season spawning11,12,13. Eyestalk ablation in brachyuran crabs has also been done to study molting25,32,33, hormonal regulation18, gonad maturation34, and induced breeding and reproductive performance35,36,37,38,39. Anesthesia via immersion in 2-phenoxyethanol was used as it is comparable to the use of tricaine methanesulfonate (MS-222) in arthopods but cheaper and does not require the use of additional buffer40. Unilateral or bilateral eyestalk ablation influences the physiology of the crustacean. Eyestalk ablation following the protocol stated in this study also influences the ovarian maturation rate of mud crabs. In the control treatment (without eyestalk ablation), 43.33% ± 5.77% of female crabs had an immature ovary (stage-1). However, in the same rearing period (30 days), eyestalk-ablated female crabs had pre-maturing ovaries (stage-3; 56.67% ± 11.55% and 53.33% ± 15.28% with the cauterization and surgery techniques, respectively), which shows that eyestalk ablation can increase the gonad maturation of mud crabs. Previous studies have also reported that the ovarian development of intact crabs (without eyestalk ablation) is slower than that of eyestalk-ablated crabs25,31. Due to the slower gonadal development in intact crustaceans, eyestalk ablation is widely done in commercial prawn and shrimp hatcheries. In this protocol, the eyestalk-ablated female crabs achieved higher percentages of ovarian maturation compared to the female crabs without the eyestalk ablation treatment (Figure 3).
The gonad maturation of the mud crab is regulated by hormones21,41,42. The eyestalk contains important endocrine glands (i.e., the X-organ-sinus gland complex) that play vital roles in the gonadal maturation process of mud crabs18,21. Unilateral eyestalk ablation, either by cauterization or surgery, damages one of the major endocrine glands that is involved in the synthesis and release of inhibiting hormones (e.g., VIH), thereby resulting in a higher level of gonad-stimulating hormones (i.e., VSH).
The ovarian maturation stages of Scylla spp. can be differentiated by observing the ovarian tissue coloration with the naked eye29,30,43. Translucent or creamy white ovarian tissues are indications of immature ovaries29,30,43,44. In this study, immature ovaries (stage-1) were still found in the group of female crabs without eyestalk ablation due to the slower ovarian maturation process. However, the crabs in the eyestalk-ablated groups (both by the cauterization and surgery techniques) mostly showed pre-maturing ovaries (stage-3), with some individuals exhibiting fully matured ovaries (stage-4). Therefore, the protocol of eyestalk ablation described here can be used to increase ovarian maturation in female mud crabs. This protocol can also be applied directly to wild-collected mature female mud crabs to hasten their seed production. To evaluate the effectiveness of cauterization and surgery methods on mud crab gonad maturation and to ensure the accurate estimation of molting duration, sexually pre-mature crabs were used. After the (induced) molting of sexually pre-mature female crabs, we noticed that their ovaries were still in the immature or early developing stages29,45. After 30 days of rearing the newly mature female crabs (either eyestalk-ablated or without eyestalk ablation), the ovarian development stages (stage-1 to stage-4) were determined by the color of the ovarian tissues. This protocol encourages the use of the cauterization technique to perform eyestalk ablation in mud crabs to avoid any hemolymph loss and prevent infection at the ablated sites. Cauterization immediately seals the wound, whereas the surgery technique takes time for the wound to heal and this would allow for chance of infection. For commercial purposes, larger mature crabs, preferably at a later stage of ovarian maturation, should be selected for eyestalk ablation to shorten the time to reach the fully matured ovary stage for subsequent commerce or brood stock culture. In addition to eyestalk ablation, individual rearing with sand substrate and sufficient feeding, preferably with live feed, can increase the gonad maturation rate of mud crabs in captivity30,35,46,47.
Crustacean blood is called hemolymph and can be lost during eyestalk ablation. An excessive loss of hemolymph may lead to the death of eyestalk-ablated crabs, especially when performing surgery to remove the eyestalk. The hemolymph can coagulate in the wounded part to prevent loss. However, in comparison to the surgery technique, the cauterization technique seals the wounded part immediately, thereby preventing the loss of hemolymph and possible infection.
Mud crab mortality after unilateral eyestalk ablation with either cauterization or surgery was not found within the first 7 days. Thus, eyestalk ablation can be done with a higher survival rate. Unilateral eyestalk ablation does not hamper the survival rate of the crab33.
Stress during crab handling and eyestalk ablation may contribute to crab mortality. Proper anesthesia is needed to minimize handling stress during eyestalk ablation. In crustacean eyestalk ablation, chemical anesthetics (i.e., xylocaine, lidocaine) are used at the base of the eyestalk before eyestalk ablation14,15,17,48. However, due to the aggressive nature and large size of mud crabs, the use of anesthesia only at the base of the eyestalk is not sufficient and might result in additional stress to the animals during the injection. On the other hand, anesthesia by subjecting them to a lower water temperature is more economical and safer. The use of cold water for anesthesia in mud crabs is common and has been used in other studies due to its efficiency, simplicity, and minimal impact on recovery and survival37,49,50. In addition, future research on pain assessment following eyestalk ablation on mud crabs is recommended to highlight the change in behaviours associated with pain and stress, as evident in freshwater prawn Macrobrachium americanum51.
Although eyestalk ablation using both cauterization and surgery methods has a minimal effect on crab survival and enhances ovarian maturation, performing eyestalk ablation requires professional mastery of the techniques. The timing between the steps is critical as any delay between protocols adds additional stress for the crabs. Unlike the surgery technique, the cauterization technique is dangerous because it involves the use of flammable equipment (i.e., a blow torch and butane gas). Thus, extra caution is needed when performing the cauterization technique.
Crabs are cannibalistic in nature, and they are known to prey on others that have just completed their molt and are still in their soft-shell conditions7,52,53. Thus, rearing the crabs individually can avoid unnecessary mortality due to cannibalism. The use of individual rearing in mud crab culture is commonly practiced, both in high-density culture and pond culture, for fattening and soft-shell crab farming purposes8,53. This protocol also utilized individual rearing and maintenance. During the transportation of the crabs for rearing or commerce, the crab chelipeds are tied up securely (or even autotomized) to prevent fighting, unnecessary injury, and limb loss34.
The described protocol for eyestalk ablation should be performed with multiple persons. After completing the eyestalk ablation, non-disposable equipment (e.g., the aquarium, tray, towel, etc.) should be disinfected with 30 ppm chlorine. The crabs must be monitored at least twice per day. Any dead crabs, uneaten feed, ablated limbs, or molted crab shells should be swiftly disposed of (i.e., buried in soil with bleaching powder) to prevent any potential for disease spread.
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