Global aquaculture production has been steadily increasing over the last decade. Asian countries like Taiwan, Indonesia, Thailand and India have emerged as global leaders in shrimp production. In order to bridge the gap between world demand and supply of shrimp, many countries have undertaken intensive shrimp culture.
Disease and production problems vary during the different phases of shrimp culture. One of the most important criteria for a successful culture operation is to ensure maintaining good health of the shrimp. The environment can have a significant impact on shrimp health, growth and production. Success of culture depends totally maintaining the good health condition in shrimp with proper functions of various organs.
The hepatopancreas a digestive gland or midgut gland is an organ of the digestive tract of arthropods (Shrimp) and molluscs. It provides the functions in mammals are provided separately by the liver and pancreas. Hepatopancreas is a gland that ends in ducts that open into the stomach.
The condition and appearance of the hepatopancreas give a good indication of the feeding condition of the shrimp.
- In starved shrimp: The hepatopancreas takes on a shrunken, pale appearance
- Shrunken hepatopancreas of Shrimp: it indicates that the shrimps are underfed or are not actively feeding.
- In well-fed Shrimp: The full and dark or coloured hepatopancreas is due to the feed ingested.
- Hepatopancreas are the presence of large numbers of digestive vacuoles and the foregut a “bubble”-like or turbid appearance: the shrimp are both feeding and digesting well. The movement of the gut (peristalsis) should also be strong.
- Hepatopancreas may appear dark with full indigestible material: Digestive vacuoles are few and/or peristalsis is weak or absent.
- Hepatopancreas is empty but not excessively shrunken: this may simply indicate that shrimp need to be fed or that there is not enough feed in the pond.
- Hepatopancreas is full but there are no digestive vacuoles present: the PL has only recently been fed.
Major Functions of Hepatopancreas
The hepatopancreas is an important organ for the absorption and storage of nutrients. The hepatopancreas is a complex midgut diverticulum and acts as primary digestive organ of shrimp. It has the dual role of secreting digestive enzymes and absorbing nutrients. It is also considered a major organ for shrimp for other functions….
- Hepatopancreas synthesizes and secrets digestive enzymes for food digestion.
- Hepatopancreas absorbs digested material.
- Hepatopancreas transports the stored nutrients to the muscle, gonads and other tissues during the growth and reproductive stages.
- Hepatopancreas helps in the metabolism of lipids and carbohydrates.
- Hepatopancreas is the store house of large amounts of energy (lipids) for supplying energy during molting, starvation or reproduction.
- Hepatopancreas is an important site for the synthesis of vitellogenin and sex steroid hormones for some biosynthetic steps in these pathways.
- Hepatopancreas plays important roles during growth and reproduction process in shrimp.
- Hepatopancreas act as a site for reserves of mineral and organic products.
Functions of Various cells In Hepatopancreas
The hepatopancreas is comprised of four types of epithelial cells and each plays a different role in hepatopancreatic function.
E-cells found at the distal tips of each tubule with proximal nuclei and conspicuous nuclear bodies give rise to the other three cell types of the digestive gland.
R-cells multi-vacuolated cells occur throughout the HP and have absorptive and lipid and glycogen storage functions. They also commonly sequester mineral deposits such as calcium, magnesium, phosphorus, sulfur, and others.
B-cells large, primary secretor cells, are the primary producers of digestive enzymes in the HP and are responsible for nutrient accumulation, intracellular digestion, transport of digested material.
F-cells are responsible for protein synthesis and storage of minerals.
Factors affect to damage Hepatopancreas
The following factors are also affecting the hepatopancreas such as shrimps under stress, sudden changes of water quality or pond environment & moulting. The Healthy hepatopancreas is directly related to the growth performance and body health for shrimp directly.
Digestion: Hepatopancreas is one important digest organ which can secret different kinds of digestive enzymes. It helps for nutrients absorption in intestine. The digestive function will directly affect due to lesion of hepatopancreas & intestine. These organs will become diminution at the beginning and hepatopancreas will shrivel. These turn into pale, content of white feces and intestine become red. The feed in gut of shrimp with white feces, the nutrients are hard to digestion or absorption.
Toxification: Hepatopancreas also helps for detoxification and decomposing functions in shrimp body against hazards or toxic compounds. The damaged hepatopancreas is unable to decompose the feeding with toxin compounds and hazardous substances. The un-decomposed toxin substances will affects the intestine and especially damage of intestinal villus and lose part of the shield functions.
Excess Feeding: It is important to avoid too much feeding at one time which may lead to heavy pressure and cause damages to hepatopancreas. Also, it will affect the functions of digestion and detoxification systems. The frequent normal feeding with requires quantity can be undertaken for smooth functions of hepatopancreas.
Period for Development of Hepatopancreas
Homogeneous period: The starting feeding period of early stage of shrimp (Pl) have freak hepatopancreas function. Metabolism is the main problems during this period while bacterial infections rarely happen. It is most important to reduce the pressure on metabolism and digestion in order to promote growth, development, improve immunity, rich nutrition system, promote proper digestion etc.
Turn liver period: Shrimp after attaining stage (PL25) in grow out ponds, shrimp starts feeding for growth and development of body. But poor development of hepatopancreas affects on fast body growth and weight. This is the vital period for healthy hepatopancreas in shrimp. Diseases are easily occurring such as swelling and atrophy of hepatopancreas with various stress factors.
Envelop period: Envelop period is the mature time of hepatopancreas function with shrimp length 6-8 cm. There are one white protective envelop besides and turn into normal dark chocolate brown color. Shrimp enters into rapid growth period and also hepatopancreas located in the middle part of head region during entire culture. There are many elements related for shrimp feeding besides water quality. The healthy of hepatopancreas is also vital important in various functions for L. vannamei.
Diseases in Hepatopancreas
EMS/AHPND: Acute Hepatopancreatic Necrosis Disease (AHPND) iscurrently the most important non-viral disease threat for cultured shrimp. It is usually characterized by mass mortality during the first 35 days of culture. This disease is caused by certain strains of ubiquitous in marine and brackish water bacteria called Vibrio parahaemolyticus. Also, it is caused by various other factors like harmful physicochemical factors, less feeding rate, bad weather conditions, Poor quality seed (PL), deterioration of water quality, toxic algae, disorders & weak pond ecosystem, stress resistance, less immunity in shrimp body, growth of pathogenic population.
Gross signs EMS/AHPND at pond level: erratic swimming or swimming near the bottom of the pond, reduced growth, soft texture of the exoskeleton, partially or empty gut, unusually high mortality within about first 35 days of shrimp grow-out culture, moribund shrimp sink to bottom, etc.
Fig: A & B: Gross signs of AHPNS-infected shrimp- Pale, atrophied hepatopancreas (HP), and an empty stomach (ST) and midguts (MG), which was induced by immersion bioassay. C & D: Normal shrimp in the negative control group- showing a normal size HP with dark orange color and a full stomach and midgut. (B) and (D) are dissected individuals from (A) and (C), respectively
Sign of Hepatopancreas in EMS/AHPND:
Whitening of the hepatopancreas, reduction in size of hepatopancreas, dark spots or streaks on the hepatopancreas, Hardening of hepatopancreas, intertubular haemocytic infiltrations among HP tubules, Hepatopancreas(HP) often appears pale to whitish due to loss of pigment, the HP of shrimp is significantly shrunken, small or discolored, Often pale to white hepatopancreas (HP) due to pigment loss in the connective tissue capsule, significant atrophy.(shrinkage) of HP.
The frequent application of antibiotics and too much use of Vitamins are not suitable for shrimp health. This will affect heavy burden & pressure for hepatopancreas. Antibiotics do not only treat diseases, but also produce endotoxins which will do harm for the health of hepatopancreas and intestine. It Is better to avoid strictly antibiotic use in shrimp. The suitable amount of vitamins shall conform to the digestive ability of intestine and the proper proportion.
The all herb extracts will not do well for hepatopancreas and large application also damage to hepatopancreas. The use of high quality herbal extracts can be suitable for protecting hepatopancreas. Feed intake shall be reduced within reasonable dosage. The stop feeding will cause the consume of glycogen and fat in hepatopancreas. Reasonable reduce the feed intake is feasible, but stop feeding is inadvisable.
Affects of Poor & damaged Hepatopancreas in Shrimp Culture: Disease and production problems arise during the different phases of shrimp culture due to poor development & damaged hepatopancreas of shrimps such as less Feeding, moulting problems, soft and loose shell, cramp body, Low production, mortality, slow growth , decreases survivals rate , high food conversion ratios (FCR) ,economic losses , external infections etc. Major diseases occur in shrimps like WSSV, Taura syndrome virus (TSV), runt-deformity syndrome, vibriosis, necrotizing hepatopancreatitis (EMS/AHPND), white gut, white feces etc.
Fig: (a)Photographs of hepatopancreases from healthy L. vannamei shrimp and shrimp naturally infected with AHPND (arrows). (b) The hepatopancreas without external membrane shows atrophy and white color
Protection of Hepatopancreas
Hepatopancreas necrosis (EMS / HPNS) and White Spot Syndrome are difficult to prevent and control. These became the most prominent risk factors for shrimp culture and leading to huge losses. Ecological prevention and control is an effective method. A quality feed additive including Vitamin C, calcium gluconate & bile acids are useful to treat and stress relieve response for Hepatopancreas necrosis. This will rebuild the efficient ecosystem to maintain a balance, so that it could effectively prevent and cure shrimp hepatopancreas necrosis.
Daily protection on hepatopancreas
Hepatopancreas is most important and most versatile organ for shrimp. It helps for digestion and absorption, immunity, hematopoietic, detoxification and other functions. Once hepatopancreas is damaged, it will affect the growth of shrimp and seriously result in the shrimp death. Hepatopancreas is one of the most important detoxification organs for shrimp when the shrimp goes into the rapid growth stage. During this stage, increases harmful bacteria population and more organic pollutants in culture pond. The hepatopancreas acts tremendous detoxification function that is to transform and decompose a variety of toxic substances in the body.
Hepatopancreas also fight against external invasion expels toxins from the body. It acts like a high-load operation of a machine against any stress on outside environment, pathogens invade, overload digestion and nutritional deficiency due to its strike nature. This increase shrimp resistance to disease, relatively reduce the chances of diseases, which will naturally improve the growth phase.
The protection on hepatopancreas during liver transportation:
Liver transportation is the rapid development of shrimp hepatopancreas and also the critical period of hepatopancreas function transformation which prone to cause hepatopancreas disease. Normal shrimp liver through this period will be developed into a complete, sharp angular shape, surface covered silver liver capsule, and the color gradually becomes brown or gray-green. Because of rough feeding technique by various factors or environmental influences, liver transportation often failed to properly complete.
Vitamin C and bile acids working as good detoxifying substances along with vitamin B are helpful for the transportation of liver with appropriate amount.
Bile acid for Protection of Hepatopancreas: Bile acids are formed by the combination of the amino acid glycine or taurine with cholic acid. They are concentrated in the liver and excreted by the liver into the bile. It passed on to the gastrointestinal tract (via the bile duct) where they act as important soluble enzymes. Bile acids also facilitate the major excretion route of cholesterol. The metabolic processes of emulsification, digestion, and transport of lipids in crustaceans are unique. Lipid transport in shrimp is accomplished primarily by high density lipoprotein (HDL).
Bile acid feed supplements protect on shrimp hepatopancreas and it is an important chemical barrier to endotoxin. But also it has a significant antibacterial effect on gram positive bacteria. Bile acid acting as a deterrent and has a direct role on both lipopolysaccharides. Bile acid supplements in shrimp feed can effectively improve immunity, relieve the pressure and repair the damage of hepatopancreas by promoting the secretion of bile and accelerate the detoxing of deposited toxins. The bile acids improve the anti-stress ability.
Control Measures for Protection to Hepatopancreas in Shrimps
- EMS-free brood stock is needed to prevent EMS in pl stage. Test the larvae for AHPND/EMS by PCR before stocking ponds. Stock with healthy post larvae.
- Improves the proper farm practices.
- Establishes a balanced microbial population in pond system.
- .Closely manages water and bottom sediment quality.
- Disinfection with chlorine or ozone to eliminates multiple pathogens.
- Removes sludge regularly.
- Improve farm infrastructure with biosecure in intensive ponds.
- Monitor the pond parameters regularly.
- Avoid excess or overfeeding & provide optimal quantity of feed.
- Using biofloc technology in shrimp culture appears to be useful in preventing AHPND/EMS outbreak.
- Adopt closed re-circulatory systems or zero water exchange practice to avoid contamination.
- Ecological prevention and control is an effective method.
- Vitamin C & bile acids working as good detoxifying substances and together with vitamin B are helpful for the transportation of liver with appropriate amount
Advantages of Healthy Hepatopancreas of Shrimp in Culture
These are the major advantages of a healthy Hepatopancreas of a shrimp for successful & profitable culture such as better growth rate, more survivals, ensures better harvest, low FCR, proper feed digestion, increases immunity, less disease out breaks, proper moult cycle, avoid shell diseases etc.
There are many major elements required for the success of shrimp culture. Besides the feeding and water quality, the health of hepatopancreas is also vital for success of L. vannamei. The best pond management and health management practice to be followed in culture system for safe protection of hepatopancreas in shrimp. The healthy hepatopancreas in shrimp will boost maximum performance for the success of culture.