Determining production characteristics of dusky kob, Argyrosomus japonicus, grown in sea cages under commercial conditions in Richards Bay, South Africa

Thesis (MScAgric)--Stellenbosch University, 2019.

ENGLISH ABSTRACT: With aquaculture in South Africa being in its infancy there are many questions regarding the production characteristics of potential candidate aquaculture species, one such species being the dusky kob (Argyrosomus japonicus). Production results were obtained from the DST SU KZN Aquaculture Development Project that was implemented and managed by Stellenbosch University from 2015 to 2017 in Richards Bay, KwaZulu-Natal. The project assessed the technical, environmental and financial feasibility of farming dusky kob in sea cages. In August 2015, 25000 dusky kob fingerlings of 9 grams each were stocked into the cages. Two size classes emerged in the growth trial; the fish reached average weights of 1580 grams and 1082 grams respectively. Total FCR calculated over the course of the production period (23 months) was 2.25 at an average water temperature of 21°C. Fish size had no effect on fillet yield (%), but had a significant effect on fillet proximate composition. As fish size increased, lipid content increased and moisture content decreased. Initially, protein content increases as fish grew in size, although the rate of increase also declined. Using a copper alloy net cage to farm marine fish in an attempt to reduce or eliminate biofouling caused no significant difference in metal concentrations in meat samples derived from fish grown in traditional polyester versus copper alloy net cages. The maximum concentrations measured for the various metals in meat samples were below the upper limits as set by South African, EU and USA regulations for safe human consumption. A summary of harvesting methods used to harvest dusky kob from sea cages and the subsequent logistical cold chain, as well as general observations and recommendations regarding the production of dusky kob is provided.

AFRIKAANSE OPSOMMING: Akwakultuur in Suid Afrika is ‘n jong en ontwikkelende industrie met verskeie potensiële kandidaat spesies wat ondersoek word om produksie verwante vrae te beantwoord; een sodanige spesie is die kabeljou (Argyrosomus japonicus). Produksie resultate is verkry vanaf die DST SU KZN Aquaculture Development Project wat deur Stellenbosch Universiteit geïmplementeer en bestuur was gedurende 2015 tot 2017 in Richardsbaai, KwaZulu-Natal. Die projek het die tegniese, omgewings en finansiële uitvoerbaarheid van kabeljou produksie in hokke geassesseer. Gedurende Augustus 2015 is 25000 kabeljou vingerlinge van gemiddeld 9 gram elk in ‘n hok geplaas. Tydens produksie (23 maande) het twee grootte klasse ontstaan wat onderskeidelik ‘n gemiddelde massa van 1580 gram en 1082 gram bereik het. Die voeromset bereken oor die totale produksie tydperk was 2.25 by ‘n gemiddelde water temperatuur van 21°C. Vis grootte het geen effek gehad op die filet uitslag-persentasie nie, alhoewel, dit het ‘n noemenswaardige effek gehad op die filet vleis-samestelling. Soos vis grootte toegeneem het, het lipied inhoud toegeneem en vog inhoud afgeneem. Aanvanklik neem proteien inhoud toe met ‘n toename in vis grootte, maar die tempo van toename verminder. Die gebruik van ‘n koper allooi hok vir die uitgroei van die vis as ‘n poging om die ontwikkeling van bio-organismes “biofouling” te verminder of verhoed het geen noemenswaardige verskil veroorsaak in die metaal konsentrasies in vleis monsters afkomstig van vis in ‘n koper allooi hok teenoor vis in ‘n tradisionele polyester hok nie. Die maksimum konsentrasies wat gemeet is, was laer as die voorgeskrewe maksimum limiete vir veilige menslike gebruik soos gespesifiseer deur die Suid Afrikaanse, EU en USA regulasies. Die oes metodes wat gevolg was om die kabeljou te oes met die daaropvolgende verkoeling en vervoer is opgesom, asook algemene aanmerkings en voorstelle rakende kabeljou produksie.