Microalgae: an indispensible feed for bivalves

976 views

Published on

Bivalves are unique among the many species widely farmed for human food. Species from the mollusc group, which include mussels, oysters and clams, are dependent on phytoplankton (microalgae) throughout their entire life cycle. Wild stocks of bivalves are under pressure from overexploitation and habitat losses; environmental stresses such as introductions of new diseases and harmful algal blooms; climate change bringing altered temperature regimes and increased incidences of damaging storms; and increasingly severe ocean acidification. The aquaculture industry plays a crucial role in supplying the increasing human demand for bivalves as food, and to maintain natural populations of the species.

Published in: Education, Technology, Business
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
976
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
14
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Microalgae: an indispensible feed for bivalves

  1. 1. I N C O R P O R AT I N G f i s h far m ing t e c h no l og y January | February 2014 Microalgae: an indispensible feed for bivalves International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2014 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058 The International magazine for the aquaculture feed industry
  2. 2. FEATURE Microalgae an indispensible feed for bivalves by Eric C. Henry PhD, research scientist, Reed Mariculture Inc, USA B ivalves are unique among the many species widely farmed for human food. Species from the mollusc group, which include mussels, oysters and clams, are dependent on phytoplankton (microalgae) throughout their entire life cycle. Wild stocks of bivalves are under pressure from overexploitation and habitat losses; environmental stresses such as introductions of new diseases and harmful algal blooms; climate change bringing altered temperature regimes and increased incidences of damaging storms; and increasingly severe ocean acidification. The aquaculture industry plays a crucial role in supplying the increasing human demand for bivalves as food, and to maintain natural populations of the species. Cultured microalgae – hatchery fuel Hatcheries have long been used to enhance bivalve reproduction by providing ample feed for larvae, post-larvae (spat), and often broodstock animals to increase their fecundity. Hatcheries are also essential for selective breeding of desirable qualities into bivalve strains, and for propagating their progeny. Increasing interest in strains of bivalves selected for superior productivity and disease resistance will increase the need for husbandry of adult animals in hatcheries. Equally, further environmental deterioration in natural beds will increase the importance of broodstock conditioning in hatcheries. Hatchery production of ‘seed’ can be used to bolster or repopulate natural production grounds, or to establish new production sites, sometimes using entirely artificial installations such as floating oyster and mussel rafts. Ample feeding with microalgae is the key to hatchery productivity. Hatchery production can be boosted by improved feeding protocols, which increase the Image 1: Veliger (larva) of Atlantic oyster (C. Virginica) fecundity of the broodstock and improve the rate of survival and successful metamorphosis of larvae. Better protocols also make it possible to extend the breeding season through temperature control and supplementing diets with cultured microalgae when local seawater conditions do not permit sufficient production of natural phytoplankton. Supplemental feeding with cultured microalgae can also be used to grow settled spat to larger sizes before outplanting, which increases the rates of survival and initial growth. Cultured microalgae can also be used to speed up depuration of harmful bacteria (e.g. Vibrio) (Lewis, 2010) and shellfish toxins (Svensson & Förlin, 2004) that can contaminate harvested bivalves. Which microalgae are best for bivalves? Although hundreds of microalgae strains have been tested as feeds for aquaculture, fewer than 20 are in widespread use (Guedes & Malcata, 2012). Because these algae vary so greatly in their nutritional profiles, careful consideration is necessary in order to select the most nutritionally appropriate strains. Such algae as Spirulina, Chlorella, Haematococcus, and Dunaliella are easily mass-produced as 36 | InternatIonal AquAFeed | January-February 2014 they can be cultivated in open ponds at low cost, but they all lack the omega-3, polyunsaturated fatty acids, EPA and DHA content that is essential for most bivalves. Although various nutritional components have been well documented in some algae strains, complete nutritional profiles are known for very few of them, so it is very difficult to predict which strains are the best choice for a particular application. It is unfortunate that so many studies of the nutritional performance of microalgae have tested single strains as the only feed, when it should be obvious that no single strain is likely to provide an optimal nutritional profile comparable to what a natural mixed phytoplankton assemblage can provide. It is equally unfortunate that so many studies of bivalve feeding have failed to identify the particular strains of the algae that were used. Additional uncertainties arise because the nutritional profiles of microalgae can be strongly influenced by culture conditions, including light regime, temperature, nutrient (e.g. nitrogen, phosphate) availability, and the growth phase of the culture (exponential, stationary, declining) when harvested. Although the PUFA content of many strains has by now been well documented, sterol profiles have been more challenging to characterise, since there is far more strain-to-strain variation. This is even the case among strains supposedly of the same species, as revealed in a recent investigation of over 100 diatom strains (Rampen et al., 2010). Protein content is less variable, with a study of 40 strains of microalgae in seven algal classes finding consistently high contents of essential amino acids (Brown et al., 1997). Vitamin contents of microalgae also appear to be consistently high (Brown & Miller, 1992; Brown et al., 1999). The high-PUFA algae most widely used for bivalves include strains of Tetraselmis (Prasinophyceae); Isochrysis and Pavlova (Prymnesiophyceae); Thalassiosira, Chaetoceros,
  3. 3. FEATURE and Skeletonema (diatoms); Rhodomonas (Cryptophyceae); and Nannochloropsis (Eustigmatophyceae), the last one especially used for mussel farming. But which strains to choose for a particular application? It can be very difficult, even impossible to identify a species of microalgae based on light microscopy alone, even in the hands of taxonomic specialists. Indeed, it may not even be sufficient to identify particular strains of algae from examination of ultrastructural (visible only by electron microscopy) and some biochemical characteristics. Recent studies employing molecular genetic analysis show that strains that are indistinguishable by these features may nevertheless be genetically distinct. The extent of this problem can be illustrated by a brief survey of what has been learned about the differences among some of the various strains of four microalgae most often recommended for bivalve aquaculture: Tetraselmis, Isochrysis, Pavlova, and Thalassiosira. Tetraselmis Tetraselmis is widely used as a successful shellfish feed, probably in a large part due to high levels of cholesterol and significant EPA in some strains. Tetraselmis has also been reported to suppress pathogenic Vibrio spp. (Austin & Day, 1990; Regunathan & Wesley, Image 2: Tetraselmis microalgae Image 3: T-Iso microalga 2004), and some strains are among the few microalgae containing significant levels of taurine (Tzovenis et al., 2009; Al-Amoudia & Flynn, 1989; Flynn & Flynn, 1992). It is striking that the US National Center for Marine Algae and Microbiota (NCMA – formerly CCMP) holds some 118 strains catalogued as Tetraselmis, but only seven are identified as to species, and one of the most frequently recommended Tetraselmis species, T. chuii, is not among them! Studies of the fatty acids in nine strains (Wikfors et al., 1996) and sterols in 11 strains (Patterson et al., 1993) of Tetraselmis found wide ranges of total contents and different forms of these critical nutrients, indicating that more species diversity exists than has been recognized by traditional taxonomic stud- ies. However, molecular genetic analysis of aquaculture strains has not yet been reported. Isochrysis Isochrysis strains are favoured for particularly high levels of the fatty acid DHA, but the relationships among aquacultured strains have been unclear. Fortunately, a recent molecular genetic study (Bendif et al., 2013) has now shown that the very widelyused ‘Tahitian’ strain of ‘Isochrysis’ (which has been referred to in different studies as ‘Isochrysis sp.’; ‘Isochrysis galbana,’ ‘Isochrysis aff. galbana’, or most often simply ‘T-Iso’) is so different from other species of Isochrysis that it belongs in its own genus, now named Tisochrysis. Owing to this research we can now finally understand why strains that are I NEVER WORRY ABOUT ACTION, BUT ONLY INACTION. —Winston Churchill Are you ready to take action against food contamination and product recall risk? Wenger’s food safety and hygienic procedures should play a leading role in your production. Consider just a few of our solutions: • Corporate Project Services, an entire division dedicated entirely to food safety management systems. ? • Equipment with less potential for cross contamination and product accumulation. • Closed-loop systems and improved product transfer to reduce “fugitive” dust. • High-Intensity Preconditioner for improved pasteurization and sanitation. • Machine designs that allow easier cleaning and product inspection. • Automatic control systems with tracking, traceability and recording. Contact us now for safety measures customized for your production. Turning ideas into opportunities. PROgREssIVE AQUAFEED PROCEssINg v safe What will tomorrow bring wenger.com BELgIUm Wenger13.SafetyAQ.190x132.indd 1 January-February 2014 | InternatIonal AquAFeed | 37 TAIWAN BRAsIL ChINA TURkEY INDIA 12/19/13 3:49 PM
  4. 4. FEATURE (Bendif et al., 2011) has considerably clarified the relationships among many Pavlova strains as well as related genera, although additional strains remain to be examined. Different strains contain a remarkably diverse range of unusual sterols (Gladu et al., 1991; Patterson et al., 1993; Ghosh et al., 1998) and this sterol content may account for the widespread impression that Pavlova contributes real, though poorly characterised, value as a bivalve feed. One study has surprisingly reported that the combination of Pavlova lutheri Image 5: Thalassiosira weissflogii (unfortunately, strain not specified) and Image 4: Pavlova microalga microalgae Nannochloropsis (not much used for bivalves other than mussels) provided a feed for the European oyster Ostrea edulis that proved indistinguishable by microscopy differ so Pavlova superior to combinations of Chaetoceros widely in their PUFAs (I. galbana contains Pavlova strains, mostly designated P. luthEPA, Tisochrysis has none) and sterols (epi- eri, are also favoured for their high PUFA muelleri and ‘T-Iso’, or Tetraselmis striata brassicasterol in I. galbana, brassicasterol in content. A recent comprehensive taxonom- and Thalassiosira weissflogii (Ronquillo et al., Tisochrysis). ic Page 1 VICTAMisland:Layout 1 30/8/13 14:22 study incorporating molecular genetics 2012). Research with scallop larvae indicates that at least one Pavlova strain produces a sterol that Fatten up your bottom line. Bühler high-performance animal and aqua feed production induces metamorphosis (Alix et al., 1997; Roberts et al., 2005). systems are used by leading companies around the world. These producers know they This is a very unexpected phecan rely not just on the technology itself, but also on the support that accompanies it. A nomenon, and it is a reminder service combining local presence with global expertise both lowers feed mill operating that many gaps still remain in our costs and increases capacity utilization. To find out more, visit www.buhlergroup.com knowledge of how microalgae may affect the biology of bivalves. 8 – 10 April 2014 . Bangkok International Trade & Exhibition Centre (BITEC), Bangkok, Thailand Asia’s largest exhibition and conferences for animal feed, aquafeed and petfood production Bühler AG, Feed & Biomass, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 28 96 fu.buz@buhlergroup.com, www.buhlergroup.com VICTAM Asia 2014 is the largest trade show within South and South East Asia for displaying the latest equipment and technology used in the production of animal feeds, aquafeeds and dry petfoods. New for 2014 Now including the first ASEAN Feed Summit Supported by The Thailand Convention and Exhibition Bureau Specialist conferences The exhibition will be supported by its own specialist conferences: The FIAAP Conference 2014 Petfood Forum Asia 2014 Aquafeed Horizons Asia 2014 Innovations for a better The Thai Feed Conference 2014 Biomass Pelleting Asia 2014 Co-located with FIAAP Asia 2014 and GRAPAS Asia 2014 www.fiaap.com / www.grapas.eu Aqua_Feed-July_2011.indd 1 world. Contact details For visitor, exhibition stand space and conference information please visit: www.victam.com 28.07.2011 12:23:44 38 | InternatIonal AquAFeed | January-February 2014 Thalassiosira Strains of Thalassiosira weissflogii and T. pseudonana (in particular the strain known as 3H) are widely used in aquaculture. T. weissflogii is easy to culture but lacks DHA, whereas the 3H strain has some DHA but requires selenium (Price et al., 1987), and is so prone to form resting cysts that it can be difficult to culture reliably (Dixon & Wikfors, 1997). T. pseudonana was the first marine microalga to undergo whole genome sequencing, and the functions of many previously unknown genes are currently being identified (Armbrust et al., 2004). For this reason, the physiology of this species has the potential to be better understood than that of any other alga. Diatoms possess cell walls of silica that are very resistant to degradation and are ornamented with finely detailed markings that permit very precise morphological definition. Diatom species can therefore be identified with great confidence by light and electron microscopy. However, T. weissflogii strains have been isolated from cool-temperate and tropical
  5. 5. FEATURE danger of introducing diseases along with density culture methods (King, 2004) that can dramatically reduce water use, by facthe feed. The best refrigerated products typically tors of hundreds. Minimising water demand have a shelf-life of six months, and the best is especially important where local water frozen products may be used several years conditions are unfavourable (e.g. affected by down the line. This means that a reliable extreme temperatures, acidification, toxic The microalgae bottleneck ‘The success of a bivalve hatchery depends supply of algae can be kept on hand, available algae blooms) and treatment of sufficiently on the production of algae. Large quantities for use in any season or if an unexpected large volumes of seawater is prohibitively of high quality algae must be available when need arises. Algae costs become predictable, costly, or even impossible altogether. This and often prove to amount to less than on- shows how one innovation in hatchery needed.’ (FAO Bivalve Hatchery Manual) Production of microalgae consumes a site production once total production costs technology – in this case, a new form of major fraction of the infrastructure, labour, and inefficiencies have been accounted for. microalgae feed – can spur other innovations and other operating costs of a bivalve Success of larvae is so critical to the overall that were never anticipated when the feed hatchery. It requires specialised equipment success of a hatchery that even a relatively was developed. Bivalve aquaculture clearly and skilled labour, which entail costs with small improvement in survival or growth rate depends on continued research that will no return during the seasons when they are due to better feeding can yield great benefits. provide the improvements and innovations Because these products can be as much in microalgae feeding technologies necessary not needed. Any shortfall in algae production can result in reduction or even loss of bivalve as several-thousandfold more concentrated to ensure the future growth of the industry. production. Algae production can be affected than cultured microalgae, they are ideal by weather (where natural sunlight is used), for implementing new and innovative high- References available online FIAAPisland:Layout 1 30/8/13 14:26 Page 1 equipment failures, or human error, and it must be timed to match the demands of the hatchery. Algae produced when it is not needed (because timing of production was misjudged, or an anticipated hatch was not successful) is simply wasted and can contribute substantially to the total cost of algae production. seas, and even fully freshwater environments, so it is not surprising that different strains, although nearly identical in appearance, show different physiological traits. Microalgae concentrates One solution to the problem of ensuring reliable supplies of microalgae for hatcheries can be the use of commercially available refrigerated or frozen algae concentrates or ‘pastes’ (Guedes & Malcata, 2012; Shields & Lupatsch, 2012). These products, which are actually viscous liquids, have proven to be effective feeds for shellfish and other filter feeders. In products formulated to provide a long shelf-life, the concentrated microalgae are suspended in buffer media that preserve cellular integrity and nutritional value, although the cells themselves are nonviable. When concentrates with well-defined biomass densities are employed, the algae can be continuously and accurately dosed into bivalve cultures with a metering pump, matching feed delivery to the demands of the cultures, maximising feeding efficiency. Nonviability confers the advantage that the products pose no risk of introducing exotic algal strains. Concentrates produced at remote facilities free eed | January-February 2014 of pathogen vectors reduce the 8 – 10 April 2014 . Bangkok International Trade & Exhibition Centre (BITEC), Bangkok, Thailand Asia’s foremost exhibition and conferences for the ingredients and additives used in the production of animal feeds, aquafeeds and petfoods FIAAP Asia 2014 is the only dedicated trade show and conference organised specifically for feed ingredients, additives and formulation within the dynamic and growing region of South and South East Asia. New for 2014 Now including the first ASEAN Feed Summit Supported by The Thailand Convention and Exhibition Bureau Specialist conferences The exhibition will be supported by its own specialist conferences. They will include: The FIAAP Conference 2014 Petfood Forum Asia 2014 Aquafeed Horizons Asia 2014 The Thai Feed Conference 2014 Co-located with VICTAM Asia 2014 www.victam.com Contact details For visitor, exhibition stand space and conference information please visit: www.fiaap.com January-February 2014 | InternatIonal AquAFeed | 39
  6. 6. LINKS This digital re-print is part of the January | February 2014 edition of International Aquafeed magazine. Content from the magazine is available to view free-of-charge, both as a full online magazine on our website, and as an archive of individual features on the docstoc website. Please click here to view our other publications on www.docstoc.com. I N C O R P O R AT I N G f I s h fA R m I N G T e C h N O l O G y Successful moisture control in aquatic feeds Current challenges and opportunities in amino acid nutrition of salmonids • See the full issue • Visit the International Aquafeed website • Contact the International Aquafeed Team • Subscribe to International Aquafeed Whisky by-products: – a sustainable protein source for aquaculture Closing the food waste loop: – a new angle for insect-based feeds Vo l u m e 1 7 I s s u e 1 2 0 1 4 - JA N uA RY | F e B R uA RY To purchase a paper copy of the magazine, or to subscribe to the paper edition please contact our Circulation and Subscriptions Manager on the link above. INFORMATION FOR ADVERTISERS - CLICK HERE www.aquafeed.co.uk

×