Welcome to Expert Topic. Each issue will take an in-depth look at a particular species and how its feed is managed.
COBIAEXPERT TOPIC
1 ChinaThevastmajorityoftheworld’scobiaispro-duced inChina. In fact in 2004, the countryproduced 80.6 percent of global exportsaccordingtotheFAO.However,despitethis,there is little available information on cobiafeeds or farming strategies used by Chinesefarmers.
2 VietnamIn 2008, Vietnamproduced 1,500 tonnes ofcobia, making it the third largest producerbehindChinaandTaiwan.
Oneofthe largestcobiaoperations inthecountry is run by Marine Farms Vietnam, asubsidiaryofMarineFarmsASA,Norway.Thecompanyhasashorebasefacility,hatcherysiteand ten sea sites,which range from20m to32m indepth.The farms,which are locatednorthofNhaTrang,producemorethan1,500metrictonsofcobiaperyear,withthecapacitytoproducemorethan6,000tonsifneeded.
Not content with only Vietnamesecobiaproduction,MarineFarmsalsohasacobiaoperation inBelizewhichhasbeengrowing cobia in offshore cages since2006.
3 TaiwanTaiwan isoneof thepioneersof cobiaaquaculture. Init ial ly broodstock f ishwere caught from the wild but in the1990s, the country became the first intheworld tosuccessfullyspawncobia.By1997,thetechnologyandknow-howwasinplacetoraisesizeablequantitiesof cobia. Today, broodstock are takenfrom grow out cages and transportedto onshore ponds to spawn. Juvenilecobia (1.5-2years) is sent togrowoutponds, nearshore cages or offshorecages.
According to FAO data, cobia pro-ducers in Taiwan use both f loatingandsinkingpel letscomprisedof42-45percent crude protein and 15-16 per-cent l ipid. The FCR is approximately1.5:1.
4 USAEighty-fivepercentofseafoodintheUSAisimport-ed but there is burgeoning interest in increasingdomesticaquacultureproduction.Cobiaisapromis-ingcandidateforaquacultureproductionduetoitsrapidgrowthrateandgoodfleshquality.Thefirstaquacultureresearchonthespecieswasnoted in1975 in North Carolina, USA. Cobia eggs werecollectedoffthecoastandraisedinarearingtrial.
While the early production cycle in Taiwanfavoursoutdoorponds, juvenilecobia intheUSAtend to live in fibreglass tanks. According to theFAO,thesetanksareeitheroperatedasrecircula-tionsystems,flow-throughoracombinationofboth.
Researcheffortshavefocusedonextendingthecobia spawning season with the aim of reachingyear-roundeggproduction.Todate,eggshavebeensuccessfullyfertilizedduring10monthsoftheyear.
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canadumThe University of Miami and other US institutions have teamed up with feed manufacturing companies, producers and the American Soybean Association to develop competitive practical feeds for this emerging aquaculture species
by Jorge A Suarez, Carlos Tudela, Drew Davis, Matthew Taynor, Lindsay Glass,
Ron Hoenig and Daniel D Benetti
Cobia is the only member of thefamily Ranchycentridae. It is atropical and subtropical specieswidely distributed worldwide
(Briggs, 1960; Shaffer and Nakamura, 1989;Ditty and Shaw, 1992; Benetti et al., 2008),exceptintheeasternPacific,whereitrarely
found(Briggs,1960;Collette,1999;Benettiet al.,2008).Cobiaarerecognisedfortheirfastgrowth,excellentmeatquality,andhavebeenintensively farmed since the 1990s (Liao et al.,2004;Benettiet al.,2007).
Thesecharacteristics,alongwithexcellentmeat quality and good market demand andprice, raised enormous interest in commer-cial aquaculturedevelopmentof this species.Indeed,whilecobiawasalittleknowncandi-date species foraquacultureaboutadecadeago, today it has established itself as a topquality culturedmarine fish tropical/subtropi-calinAsiaandtheAmericas.
Technologyforreliablebroodstockspawn-ing and mass production of fingerlings hasbeen mastered at the University of MiamiExperimental Hatchery (UMEH) and otherprivate companies and government institu-tions around theworld.However,while thefundamentaltechnologyforcobiaproductionfrom egg to market is in place (Liao et al.,2004;Benettiet al.,2008;2010),manyyearsofresearchanddevelopmentarestillneededtorefinethecultureprocess,allowingcobiatodeveloponanindustrialscale,especiallyatthegrow-outstage.
Those working with the species both atthe R&D and production concur that themost crucial remaining roadblocks to be
addressed and resolved at this juncture arerelatedtofeedsandnutrition.
At the present time, feeds represent themostexpensiveitemoftheproductioncostsfor cobia, and the inability to provide asustainable, high-quality feed that meets theenergetic and nutritional requirements ofthese fast growing fish continues to eludeproducers. Top quality diets with high inclu-sion levels of fishmeal and fish are avail-able but costs are prohibitively high frombothecologicalandeconomicalperspectives.Therefore, thecollectivegoalof researchers,feed manufacturers and producers is to for-mulate,developandmanufactureecologicallyefficient and economically viable diets thatwillmeetthenutritionalrequirementsofthisspecies.Thisreviewsummarisestheseefforts.
Theevaluationoffeedingredientsiscrucialtonutritionalresearchandfeeddevelopmentforaquaculturespecies. Inevaluating ingredi-ents, there are several important points thatmust be understood to enable the judicioususeofaparticularingredientinfeedformula-tion(Glencrosset al.,2007).Thedetermina-tionofnutrientdigestibility isthefirststepinevaluating the potential of an ingredient foruseinthedietofanaquaculturespecies(Allanet al.,2000).
Aconstraintfortheexpansionofcobiaaqua-culture is the availability of high quality formu-
lated diets which reduce or eliminate fishmealprotein.Suitablereplacementsareoftenofplantorigin,buttheevaluationofnutrientdigestibilityin new ingredients should be an initial step inevaluatingitspotentialforfishmealreplacement.Therefore,theapparentdigestibilitycoefficients(ADCs)ofproteinandaminoacidsofanovelvariety of non-GMO soybean meal, Navita™,andanindustrystandardsoybeanmeal(defattedsoybeanmeal/roasted solvent-extracted),wereevaluated at University of Miami for juvenilecobia, Rachycentron canadum. Results indicatedthattheNavita™ishighlybio-availabletocobia,asADCsforproteinandaminoacidsobtainedfor this ingredient were significantly higher fornearly every analysed component of the feedthan the ADCs of the conventional soybeanmeal. ADCs crude protein were 81.8% and68.5%, respectively, for Navita™ and conven-tionalsoybeanmeal.Similarly,ADCsofselectedamino acids ranged from 68.3-108.6% for theNavita™ meal, whereas the same coefficientranged from 41.4-97.8% for the conventionalsoybeanmeal.Findingsfromthepresentexperi-ment highlight the potential of Navita™ as asuitable FM replacement in cobia diets andshould help to maximize cobia growth whileminimising the excretion of fish metabolites(Daviset al.,2012).
Reviewing cobia nutritionIn their thorough review of cobia nutri-
tion, Fraser and Davies (2009) pointed outthe importance of paying special attention tothe amino acid requirements when replacingfishmealwithalternativeproteinsources.Chouet al. (2004)mentions thatmethionine is theprimary limiting amino acid replacement instudiesoffishmealwithsoybeanmeal.Lungeret al.(2007)foundthattheaminoacidtaurinesupplementationatalevelof5gkg1dryweight,increased weight gain and feed efficiency incobiafeddietswithhighlevelsofplantprotein.
Fraser and Davies (2009) conclude thatnutritionalstudiesoncobiaarelimitedbecausemosthavebeenconductedusingjuvenilefishwith much lower weights than harvestablesize.Thecobiacommercialweightisbetween4 and 10 kg; however nutritional require-ments have only been examined in juvenilefishweighing50g.Althoughdifferencesintherequirementswereminimal,itwouldstillhaveahighimportantcommercialimpact,especial-lyconsideringproteinandlipidsarethemajordietarycomponentsinfishdiets.Theaccuracyof the nutritional requirements would notonlyhaveapositiveeconomicimpactontheindustry,butalsodecreasetheenvironmentalpollutionbydecreasingnutrientloadingintheaquaticecosystem.AsreviewedbyWelchet al (2010), the importanceof the responsibleuse of natural resources such as fishmeal,fish oil and vegetable crops to ensure theenvironmental sustainability of aquafeeds iswellrecognised.
Although nutritional principles are similarfor all animals, the amounts of nutrientsrequiredvaryamongspecies.Thereareabout40essentialnutrientsinfishdiets(Akiyamaet al.,1993).AccordingtoTacón(1989),nutri-tionalrequirementsinthedietofallculturedaquaticspeciesmaybecategorizedunderfivedifferent nutritional groups: proteins, lipids,carbohydrates,vitaminsandminerals.
Major nutrient requirements for juvenile cobia
Protein:Oneofthemostimportantnutri-entsinthedietofmarinefishisprotein.Thisis attributed to two factors, which are thehighcostoftheingredientandtheorganisms’high protein nutritional requirement. Excessprotein not only increases feed costs but italso increases the excretionof nitrogen intothe environment. The first article used todetermineproteinrequirementsincobiawasthatofChouet al. (2001),whodeterminedby regressionanalysis, aprotein requirementof44.5%.Craig,SchwarzandMcLean(2006)conductedafactorialstudywithtwolevelsofcrudeprotein(40%and50%)andthreelipidlevels(6%,12%and18%).Theauthorsfoundasignificantdifferenceinfeedefficiencyof7.4g cobia fedwith the lowest levelofprotein.On the contrary, when the authors usedlargercobia(49.3g)nosignificantdifferencesin feed efficiency were found between thedifferentlevelsofprotein.
Amino acids: The nutritional value of aproteindiet is influencedbythecompositionofitsaminoacids.Forthisreason,theproteintobeusedinpracticaldietformulationsmustbe based on digestible amino acid profileand quantitative amino acid requirementsin the targeted species. In cobia, studies ofamino acid requirements are limited, onlytwoof the ten amino acids havebeen con-sidered essential (Wilson 2002). Zhou et al.(2006)determinedmethionine requirementsin juvenile cobia. The authors state that formaximumgrowthandlowerfeedconversionratio,therequirementofmethionineis1.19%(drydiet) in thepresenceof0.67%cysteine,correspondingto2.64%dryweightofdietaryprotein.
For lysine,Zhouet al. (2007)determinedtherequirementsinjuvenilecobia.Theresultfor lysine requirements were 2.33% and5.30% dry weight of dietary protein. Thesevaluesofmethionineandlysineareinaccord-ance with the requirement values of otherimportantfishspeciesinaquaculture(Wilson2002).Recently,Renet al.(2012)determinedthe requirementsof arginineon thebasisofSGR and FER. The optimal dietary argininerequirementsofjuvenilecobiawereestimatedtobe2.85%ofthedietand2.82%ofthediet,respectively.
Lipids: Lipids are an important source ofhighlydigestibleenergy,inparticular,freefatty
acids derived from triglycerides constitutingthemajorenergysourceformuscleinalmostallanimals.Theyarealsokeycomponentsofcellular and subcellular membranes (phos-pholipids, sterols, etc.). Performing functionsasbiologicaltransportersintheabsorptionoffat-soluble vitamins are precursors of pros-taglandinsandhormones(FenucciandHaran2006). For juvenile cobia, the lipid require-ment was estimated at 5.76% (Chou et al.,2001).Wanget al.(2005)usedthreeisopro-teicdiets(47%protein)withthreelipidlevels(5%,15%and25%drymatter).Theauthorsfound no significant differences in growthbetweenthecobia(7.7g)feddietscontaining5percentand15percentlipids.Howeverthecobia fed 25 percent lipid had a significantreduction indailydiet consumption, suggest-ingthatlipidlevelsabove15percentreducedgrowthduetodecreasedfeedconsumption.
Carbohydrates: Because cobia commer-cial feedscontainstarchandcerealproducts,related research on carbohydrate require-ments are very important. Schwarz et al.(2007) suggests that cobia are able to useup to 360g/kg-1 of dietary starch from lowmolecularweight carbohydrate such as dex-trin. Webb et al. (2009) determined thatcobia can use carbohydrates to levels of340g/kg-1(drydiet)withanoptimumenergyprotein of approximately 34mg protein kJ-1metabolisableenergy.
Vitamins:Vitaminsarenutrientsnecessaryforgrowth,health,andreproductionoforgan-ismsandare required invery small amountsin fishdiet.Maiet al. (2009)determinedtherequirementsofcholineinjuvenilecobia.Therequirement determined by ‘broken line’ forweight gainwas 696mg/kg-1 choline diet ascholine chloride. Unfortunately there is notenough informationon the requirements forvitaminsandmineralsinCobia.
Future research areasFor the future we propose the following
researchintheareaofcobianutrition:• Determine nutritional requirements at
differentsizesclasses• Further requirements of amino acids,
vitaminsandminerals• Continue research replacementof fish-
meal and fish oil to alternative sourcesofproteinandlipid
• Complement existing information ondigestibility and energy balance of pro-tein ingredients of plant and animalorigin
• Monitoring the quality of commercialfeeds,usedbytheindustry
• Implementation of managementpractices
In conclusion, the collaborative effort ofresearchers, feedmanufacturersandproduc-ers are driving steadfast progress towardsdevelopingpracticalandeconomicaldietsfor
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EXPERTT●PIC
cobiaatalldevelopmentalstages.Governmentsupportaswellasinterestandfundinggener-ated by American Soybean Association andits various affiliated groups have been ofparamount importance in advancing knowl-edgeandtechnologiesthefield.Theindustryis much further ahead than it was about adecade ago. It is recognised that enhancedknowledge and better nutrition are allowingcobia aquacultureproduction tocontinue toexpand exponentiallyworldwidewhilemov-ingawayfrominadequatedietsandtrashfish.The development of an ecologically efficientand economically viable cobia aquaculture
industry is and will continue to benefit allstakeholders,fromproducerstoconsumers.
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EXPERTT●PIC
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