Nutrition & Health
Rotifers as live feed in shrimp hatcheries, Is still an open option?
M.R.Kitto* and Regunathan C.**
*Assistant Professor, Faculty of Marine Science, King Abdulaziz University, P.O. Box : 80207, Jeddah 21589, Saudi Arabia. Email: firstname.lastname@example.org
**Aquaculture Specialist, 228 B, East of DVD School, Kottar, Nagercoil, Tamil Nadu, India. E mail : email@example.com(Corresponding Author)
Strolling down shrimp live feeds memory lane
Shrimp hatchery technology has been subjected to constant flux and refinement since the debut created by Motosaku Fujinaga of Japan in 1933 (Hudinaga, 1935). With the booming of commercial larviculture, constant efforts were made towards improving larval health and survival. Early larval rearing on initial days was entirely reliant on microalgae as live feeds yielding in comparatively lower and inconsistent survival owing to fluctuations in their nutritional quality. This prompted industry to seriously look out for a supplementary and if possible a replacement diet. The result from intensive research was the introduction of numerous artificial off the shelf formulated diets. As total replacement of algae has not been commercially possible, live feeds are still a prerequisite for successful shrimp larviculture. Other milestones in commercial shrimp larval rearing were popularization of Artemia as live feed for the late Mysis as well as PL stages and Artemia enrichment techniques. The rotifers drew attention among researchers as intermediate live feed for shrimp larvae due to their size falling between microalgae (5-50 µm) and Artemia (400 µm total length) and have been evaluated. Initial trials especially with non-enriched rotifers led to tagging them inferior to Artemia nauplii, and the former became obscure and out of conventional penaeid larviculture practice.
Rotifer back in feeding regime
Re-emergence of Asian shrimp boom after the disease crisis in late 1980s and 1990s has raised the question of sensible costing per quality postlarva produced. Similarly, nutritional breakthroughs and launching of selective essential fatty acids (EFA) enrichment diets in the mid-90s started drawing the significance of rotifers back again into early penaeid larval rearing . Due to their non-specific feeding habit they can be used as ‘biocapsules’ by enriching with nutrients and transfer these substances to larvae by feeding nutrient boosted rotifers. Also renewed efforts were made to replace Artemia with rotifers in larval rearing considering improved rotifer energetics per animal after enrichment.
Trials with Algamac-2000 enrichment actually showed a superior uptake of DHA by rotifers compared to Artemia (Phil Boeing, Pacific Seafarms International S.A. de C.V., Mexico). It appears the Artemia retro-convert DHA once it reaches a certain level in their system. The co-author researched on differential rotifer enrichment diets for F. indicus larval rearing and concluded that Protein Selco enriched rotifer could replace non-enriched Artemia from Zoea 2 (Z2) to still Mysis 2 (M2) stage with similar survival and till M3 stage with non-significant survival compromise (Regunathan, 2005). Research studies also included enriched rotifers in larval feeding regime (L. vannamei) from Z2 to M3/PL1 at densities 20-40/ml/day (Naessens et al., 1995; Wouters et al., 1997). Recently Yahyavi and Takami, (2007) reported better survival with cod liver oil enriched rotifer than non-enriched Artemia.
The key of differential enrichment
Large-scale rotifer culture systems will certainly win the cost-battle against live Artemia nauplii (Dallas E. Weaver, Scientific Hatcheries, USA). Rotifers have the ability to proliferate on a host of food materials in addition to phytoplankton, such as bacteria, vegetable juice, shrimp meal, rice bran etc. Yeast is not advised as a dependable feed owing to its characteristic property of unpredictable culture crashes. The best rotifer feeding regime to shrimp postlarvae would be to feed differently enriched rotifers for different stages. Tetraselmis and Nannochloropsis combined have the nutritional content to meet the protein and DHA enrichment profile for rotifers before feeding to Mysis 1 and 2 stages. Mysis 3 to PL 5 need rotifers totally enriched with cod liver oil + sardine oil emulsions. Zoea 2 to PL1 fed Cod liver oil enriched rotifers registered highest growth and survival than non-enriched Artemia for F. indicus in a study in Iran (Yahyavi and Takami, 2007). Recent study by the senior author feeding cod liver oil-enriched rotifers for F.indicus larvae yielded 44 % survival from Mysis to PL5, however noticed drastic reduction in rotifer consumption after PL3 stage.
Indirect advantages of rotifer feed include supply of natural growth hormone like substances present in adult female eggs (Gallardo and Hagiwara, 2006). Antibiosis fractions have been recognized in the spray dried powder of the Prasinophyte alga, Tetraselmis (Austin and Day 1990) recommended for enrichment. The inhibitory activity by Tetraselmis suecica toward Vibrio spp. was confirmed in vivo in a commercial hatchery of F. indicus (Regunathan and Wesley, 2004). Selective enrichment of rotifers with probiotics would reduce the cost compared to addition of huge volumes of the same added to culture water or at least by reducing the number of applications.
The future curve
Certainly the success of penaeid larvae rearing systems using rotifers in areas where Artemia and enrichment diets are prohibitively expensive or unavailable would indicate that they are an alternative worth considering. As Leland Lai, Aquafauna Bio-Marine indicates, there are also a wide number of choices of enrichments from Super Selco, fish emulsions to heterotrophic algae like Schizochytrium (AlgaMac) and Crypthecodinium (AquaGrow).
Rotifers are endowed with certain unique biological characteristics: small body size and round shape, slow swimming speed and habit of staying suspended in the water column, easily enriched with external nutrient resources and high reproduction rate and possible high density of culture populations. Rotifers are osmo-conformers and can tolerate any level hypo / hyper salinity ranges. Wullur et al., (2009) found that body length and width of minute monogonont rotifer, Proales similis (mean±SD; 83±11 μm and 40±6 μm, respectively) is 38.1% smaller and 60.3% narrower than that of Brachionus rotundiformis. Food energetics feeding penaeid mysis with the newly discovered monogonont rotifer, Proales similis are pressingly wanting for the global shrimp hatchery industry.
Benefit or Burden ?
Today, Culture Selco costs 5 cents (0.05$) to produce 1 million rotifers. DHA Protein Selco (as enrichment diet for rotifers) costs 5 cents (0.05 $) to enrich 1 million rotifers. Summing up, 10 cents (0.1 $) are required to produce and enrich 1 million rotifers. As 10,000 million rotifers need to be cultured and enriched for ten days (until PL5), producing every 1000 PL5 by feeding DHA enriched rotifers alone (without the use of Artemia nauplii) requires 50 cents (0.5 $). So, 500 $ is spent on rotifer production and enrichment to feed and produce 1 million PL5. Unlike hatcheries of yesteryears, today’s hatchery farmers do not hatch (Instar I) more than 4 kilogram Artemia cysts to produce 1 million PL5 that costs equally the same figure (500$). It is now a quandary about decision making to opt for enriched rotifers alone or just-hatched Artemia nauplii, especially for the Z2 to PL1 stages. Partial Artemia replacement studies also deserve attention.
Dhert and O’Brien (2004) assertively opine the following: Unlike Artemia, which is largely a commodity item, rotifers need to be raised at farm sites and nutritionally tailored to the requirements of species being cultured. During even the first steps of mass rearing rotifers, many choices critical to survival and quality need to be made in terms of feed selection, rearing strategy, and tank design. The skills and cost of personnel, available infrastructure, rotifer strain, and water quality in the hatchery are other parameters that determine the choices for a particular diet and rearing system. Financial limitations and regional/ cultural concepts also influence the degree of technical input in rotifer diets and culture systems. But the rotifers can consistently ever contribute to the production of healthy, nutritionally balanced feed in a convenient and cost-effective manner.
Authors of the present review feel that the cost for culturing live algae used for enrichment could be drastically curtailed in the new millennium by using agricultural fertilizers and the partial supplementary utilization of underutilized waste products like sterilized sardine pastes or sugarcane molasses extracts or rotifer culture media waste water and / or seaweed liquid fertilizer extracts of Ascophyllum or sterilized trash fish waste water. Modern technologies where probiotics are involved in shrimp larviculture, employing rotifers as starter live feed holds much promise as live-feed mediated delivery of probionts efficiently incorporates the benign bacteria to the targeted shrimp larvae. Modern day techniques for bacterial control vouch for a novel transformation as such by not killing bacteria but to have a ‘befriend them’ approach. Bioencapsulating the rotifer gut contents with vaccines, drugs, immunostimulants, nutraceuticals and any bioactive compounds shall never be a stumbling block in the present day biotechnological rearing era. Adopting judicious and sensible management procedures can improve the reliability and consistency of live feed rotifers in shrimp hatcheries.
Artemia price sensitivity, future availability and pricing trends could catch the shrimp farmer unawares – surprised and unprepared, because of year after year dwindling GSL stocks in USA. To the commercial end users of Artemia cysts, naupliar size, ease of shell removal, biochemical contents are all equally important also are factors of price, hatchability, and availability. What is the prognosis about future Artemia cyst supplies and demand is a tough query to answer.
Weighing and outweighing the thought of rotifer as benefit or burden in shrimp hatcheries depends upon the geo-specific viability of regional postlarval market economy, trends and prices. Regarding the component of environmental uncertainty impairing the quality of just-hatched nauplii, Artemia really fails to achieve recognition, despite its off-the-shelf eminence. It is the onus of R&D organizations and industry to work towards replacement of Artemia by rotifer.
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