Broodstock Nutrition And Management In Crustacean

Dharmendra Kumar Meena*., Pronob Das¹., Md. Shahbaz Akhtar²., Sekar M¹.,and Satendra Kumar¹.

*Central Inland Fisheries Research Institute, Barrackpore, Kolkata, 700 120

1. Central Institute of Fisheries Education, Mumbai, 400 061

2. Directorate of Coldwater Fisheries Research, Bhimtal, 263 136

Corresponding author: Dharmendra Kumar Meena

* Email : dkmeenafnb@gmail.com

The future of aquaculture production, as in other animal production systems, is towards greater control of the physical, chemical and biological variables surrounding the production system. The trend from collection of wild fry to the development of hatcheries for fry production, from the use of wild spawners to the use of maturation systems and ultimately closing the reproductive cycle to use domesticated and selected stocks is clear. At the same time, there is an increasing trend towards production efficiency and cost-effectiveness, not least in the hatchery stage, particularly where the supply — demand situation progresses from quantity production to quality production. These trends are becoming more evident in all forms of commercial aquaculture. Broodstock and larval nutrition are key elements underpinning this progress towards greater control and domestication. However, there is substantial work to be done if rearing of aquaculture species is to approach the level of control and understanding which are evident in the poultry, swine and ruminant sectors. Research into shrimp broodstock nutrition is gaining importance with the increasing use of domesticated and genetically selected stocks for aquaculture. Also,given the high cost of feed in a captive broodstock maturation facility, estimated at around 50% of total cost, as well as a heavy reliance on fresh feed items such as squid, mollusk meals and polychaete worms which may vary in quality and availability, there is a demand for feeds specifically formulated for use in maturation diets. It has also been pointed out (Doyle, personal communication) that the development of genetically improved lines of shrimp may benefit from a simultaneous development of feeds specifically tailored to individual strain requirements.

During penaeid shrimp maturation, nutrient reserves, mainly from the hepatopancreas, are mobilised to support ovarian and testicular maturation, gametogenesis and vitellogenesis (Harrison, 1990; 1997). Tissue reserves in the hepatopancreas can be depleted rapidly so that the diet becomes the most important contributor of nutrients to the developing egg.

This is particularly true when, as is the case in most captive maturation facilities, eyestalk ablation is used to accelerate the process of gonadal maturation. The hormonal and metabolic changes that come around during such forced maturation may take place when the nutrient reserves are insufficient to support rapid ovarian development placing an even larger burden on the diet as a source of essential nutrients.The nutrition of penaeid shrimp broodstock has recently been reviewed (Wouters et al., 2001a). The authors recognize that there is a dearth of information in the scientific literature on the subject, possibly due to the expense and complexity of running sufficiently rigorous nutrition experiments on shrimp broodstock. In addition, much of the research has been carried out with fresh feeds, either alone or in combination with formulated diets or dietary supplements.

LIPIDS
Due to the importance of lipids in crustacean maturation, much of the work carried out to date has focused on this aspect, particularly the requirement for highly unsaturated fatty acids (HUFA) and phospholipid. During maturation, lipids are mobilized from the hepatopancreas in many species and dietary lipids rapidly processed for transport to the developing ovaries.Total lipid does not appear to be important although Wouters et al. (2001b) reported that excessively high total lipid in the diet had an adverse effect on ovarian maturation and feed consumption, possibly due to satiation. However, the average lipid level in commercial broodstock diets (10%) appears to be around 3% higher than in grower feeds used in commercial culture ponds.

Highly unsaturated fatty acids (HUFA), especially 20:5n-3 and 22:6n-3, are abundant in ovarian tissues and are believed to be an important component of live and formulated maturation diets. Diets deficient in n-3 HUFA have been found to have a negative effect on ovarian development, fecundity and egg quality (Wouters et al., 1999a).Arachidonic acid (20:4n-6; AA) has been detected at high levels in the ovaries of wild shrimp and is also abundant in some of the best fresh feed items such as polychaetes (bloodworms), clams and mussels (Harrison, 1997). The n-6 HUFA are known to be precursors of the prostaglandin hormones, which act in reproduction and vitellogenesis. According to Wouters et al. (2001a), formulated maturation diets appear to be deficient in AA as well as relatively low eicosapentanoic acid (EPA) levels. It has been proposed that the ratio of n-3 to n-6 levels in the diet is important and that it should be around 2—3 to 1 (Wouters et al., 1999b).Phospholipids, mainly phosphatidylcholine and phosphatidylethanolamine appear to be predominant in the shrimp ovary and there seems to be a requirement for phospholipids in the diet. Several studies (Ravid et al., 1999; Wouters et al., 1999b) have demonstrated the effects of phospholipid levels in the diet and it has been suggested that broodstock diets should contain more than 2% phospholipid to ensure that 50% of total egg lipid is in this form (Cahu et al., 1994).

Cholesterol is the precursor of steroid hormones and it is known that shrimp have a requirement for cholesterol in the diet. Cholesterol is stored in the hepatopancreas and is mobilized during maturation. Some of the live feed organisms used in maturation diets have relatively high cholesterol levels (e.g. squid, clams) although to date there has been limited research into the effects of dietary cholesterol on maturation and reproduction (Wouters, 2001).During maturation, the level of triacylglycerides (TAG) in the ovaries increases as they are incorporated into the egg and decrease after spawning (Ravid et al., 1999; Wouters et al., 1999b). Triacylglycerides appear to be the principal energy source in eggs and nauplii and their importance in reproduction, and egg and postlarval quality has been shown (Palacios et al., 1998; 1999).

PROTEIN AND AMINO ACIDS

Maturation is a time of intense protein synthesis and it is likely that the requirement for protein is higher at this time (Harrison, 1997). Wouters et al. (2001a) report that the protein content of formulated diets in their studies was around 50% but that this was still low compared to the level in fresh feeds.

Some studies have shown changes in protein content of the ovaries associated with egg development and spawning, and with spawning success. Harrison (1997), found an increase in ovarian protein levels associated with ovarian development followed by a sharp decrease after spawning in the shrimp Paratelphysa hydrodromaus and several authors have noted a similar increase in farmed penaeid shrimp (Castille and Lawrence, 1989). A marked difference has also been noted in the protein content of the hepatopancreas and ovaries of wild and domesticated females of Litopenaeus vannamei with good repeat spawning performance which have been found to have significantly higher protein content than females with poorer spawning performance (Palacios et al., 2000).

CARBOHYDRATES

Carbohydrates do not appear to be essential for shrimp broodstock diets although Palacios et al. (1998; 1999) related egg glucose levels with larval quality and broodstock condition. Carbohydrates can be used as cost-effective ingredients to contribute to glycogen accumulation in the hepatopancreas as well as providing other benefits in the broodstock diet, acting as binders and possibly playing a role in transport of nutrients in the hemolymph (Harrison, 1997).

VITAMINS AND MINERALS

Detailed vitamin and mineral requirements for shrimp broodstock diets are relatively unknown with only a few studies on vitamins A, C and E. Alava et al. (1993) found that ovarian maturation was slower when fed a diet deficient in either vitamins E, A and C. Vitamin E appears to be important in crustacean broodstock nutrition.Chamberlain (1988), reported a correlation between vitamin E deficiency and the percentage of abnormal sperm in Litopenaeus setiferus and Cahu et al. (1991) found an improvement in hatching rate with increasing dietary vitamin E correlated to increasing—tocopherol levels in the egg.Wouters et al. (1999b) found a similar correlation to that observed by Cahu et al. (1991) between spawn and hatch quality with a-tocopherol levels in wild spawners and nauplii of L. vannamei. They found that mature

ovaries and nauplii contained higher levels of —tocopherol than immature and spent ovaries. Harrison (1997) also speculated that vitamin E in the egg yolk may also act as a natural antioxidant.

Harrison (1997), suggested the importance of dietary vitamin A due to its accumulation in the ovaries of crustaceans during maturation. Vitamin C content of eggs of Fenneropenaeus indicus are also influenced by the levels in the diet, and high hatching rate has been related to high ascorbic acid levels in the eggs (Cahu et al., 1995). Harrison (1997) assumes that vitamin D is important in broodstock diets due to its probable role in calcium and phosphorus metabolism in crustaceans.Harrison (1990) discussed the possibility that mineral deficiencies or imbalances could have a negative impact on crustacean reproduction and may play a role in oocyte resorption, reduction in reproductive performance and egg quality. Studies into mineral requirements are rare due to several complications (Wouters et al., 2001a). Where studies have been conducted, diets were formulated with mineral mixes with added calcium, phosphorus, magnesium, sodium, iron, manganese and selenium (Marsden et al., 1997; Xu et al., 1994).

Spent broodstock of L. vannamei had lower levels of calcium and magnesium in the muscle and lower magnesium levels in the hepatopancreas (Mendez et al., 1997), possibly due to a combination of dietary deficiencies and losses through moulting and transfer to the eggs. Copper also decreased in the hepatopancreas, possibly through transfer to the ovaries, although it increased in the muscle tissue. It is clear that more studies need to be undertaken into mineral nutrition in broodstock diets.

CAROTENOIDS

Crustaceans cannot synthesise carotenoids de novo, and a dietary source of these pigments is required. During sexual maturation, most crustaceans accumulate carotenoids in the hepatopancreas and during vitellogenesis, these are transported in the hemolymph as carotenoglycolipoproteins to accumulate in the eggs as part of the lipovitellin protein. Dall (1995) found that free astaxanthin levels in the developing ovaries of Penaeus esculentus increased from 2 to 34 ppm and in the digestive gland, from 20 to 120 ppm.

Carotenoids, especially astaxanthin, are strong antioxidants and probably play a role in protecting the broodstock nutrient reserves and developing embryos from oxidation (Dall et al., 1995; Merchie et al., 1998). It has also been suggested (Harrison, 1997) that they act as pigment reserves in the embryos and larvae for the development of chromatophores and eyespots, and as a vitamin A precursor (Dall, 1995).

Pangantihon-Kühlmann and Hunter (1999) found that astaxanthin supplementation (50 mg/kg) of the diet resulted in increased egg production in Penaeusmonodon but could not demonstrate any benefit of astaxanthin supplementation on either hatching rate or metamorphosis to zoea 1 stage.

MISCELLANEOUS FACTORS

Hormones

It has been suggested that some of the more successful live feed organisms may provide benefits through the provision of hormones or their precursors. Naessens et al. (1997) speculated that part of the reason for the success of reproductive adult Artemia biomass supplementation of the diet of L. vannamei broodstock could be due to the presence of specific hormones or analogous peptides in the Artemia that provoked a response in the shrimp. Bloodworms used in maturation have also been found to contain methyl farnesoate, an ecdysone hormone that has been shown to increase reproductive performance in the spider crab Libinia emarginata (Laufer et al., 1987), L. vannamei (Laufer et al., 1997), P. monodon (Hall et al., 1999) and the crayfish Procambarus clarkii (Laufer et al., 1998). In P. clarkii, the hemolymph titer increased from basal levels during early vitellogenesis, peaked during mid-cycle and then returned to basal levels when the ovaries were in late vitellogenesis.

Nucleotides

Nucleotides, the basic building blocks of nucleic acids, are recognised as important elements in mammalian nutrition especially during periods of rapid growth or physiological stress (Van Buren, 1994) and also appear to play a key role in the immune system. Traditionally, nucleotides have not been considered essential nutrients although de novo synthesis and salvage pathways are thought to be costly processes in metabolic terms. Several studies have demonstrated that dietary sources of nucleotides can have beneficial effects and the term 'conditionally essential' has been used to describe their role in nutrition (Carver and Walker, 1995).

Exogenous sources of nucleotides are thought to optimise the functions of rapidly dividing tissues, such as those of the developing embryo and young, and the reproductive and immune systems.Most aquaculture diet ingredients of animal and plant origin contain nucleotides although there are differences in the concentration and availability. Nucleotide content is particularly high in ingredients such as fish solubles, animal protein solubles, fishmeal, legumes (adenine is particularly high in blackeyed peas), yeast extracts and unicellular organisms such as yeasts and bacteria that are rich in RNA or DNA (Carver and Walker, 1995; Devresse, 2000).

Devresse (2000) noted that the low digestibility of whole yeast compared to yeast extract may be related to the protein (nitrogen) solubility as yeast extract has much higher protein solubility than whole yeast. He also noted that, although fish solubles are highly digestible, they leach easily in water affecting availability.

Reproduction and egg development have a high requirement for RNA and DNA and it may be expected that increasing the availability of nucleotides in broodstock diets may have a beneficial effect on egg development. Recently, research has demonstrated the effect of a nucleotide-enriched diet for broodstock nutrition in aquaculture (Gonzalez-Vecino, 2002; Gonzalez-Vecino et al., 2003).

Nucleotide enrichment of broodstock diets for Atlantic halibut (Hippoglossus hippoglossus) and haddock (Melanogrammus aeglefinus) resulted in a general trend towards better spawning performance and egg quality with the nucleotide diet. Total egg yield was 30% higher in the halibut fed with the nucleotide diet and the relative fecundity, mean egg density, hatching rate and survival of yolk-sac larvae were also significantly improved. Haddock fed on the nucleotide-enriched diet also had significantly higher fertilization and hatching rates. To date, no work has been published on nucleotide supplementation of broodstock diets for shrimp but it would be interesting to conduct some trials to determine if broodstock diets enriched with nucleotides might offer similar benefits in shrimp maturation and breeding. Similarly, the potential for nucleotide supplementation of diets for shrimp larvae should also be investigated.

Conclusion

There are a fewer information regarding the knowledge of bloodstock and larval nutrition of crustaceans available which creates many gaps between researcher and literature . This is partly the result of the complexity and expense of conducting research into these two areas. However, given the increasing importance of domestication in shrimp aquaculture particularly, there is a need for an increased focus on these areas. The role of nutrition in broodstock and maturation performance and in increasing larval survival and quality will be fundamental to obtaining optimal performance from domesticated stocks. Even in species where domestication is not an issue, the improvement of maturation performance and larval production remains a key goal in improving the efficiency of production systems. It is not clear how far the goal of complete replacement of live feeds may be. It is likely that this will be attained in broodstock diets long before larval feeds. Indeed, given the complexities inherent in supplying a complete nutritional package in a small particle, it may be that this goal is never reached.

However, it may be possible to supply a range of diet particles (e.g. high lipid particles, high protein particles, carbohydrate particles etc.) that are aimed specifically at providing the right mix of nutritional elements in the culture tank that will expose the larvae to the appropriate nutritional mix. Alternatively, it may be that, as expressed by D'Abramo (2002), the complexity of the ontogeny of larval nutritional physiology may mean that technical success will be based on a compromise between the desire to provide a complete diet package and the need to strive for simplicity in formulation and manufacture. In this paper maximum emphasis is given on different sources as nutrition and their beneficial effects on broodstock quality but very limited information are available regarding this module. This information will provide a base line for researcher for further studies.

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