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Rendering koi carp and creating economic value by making pet food

Koi carp is an invasive species fish in New Zealand that severely destroys the aquatic environment in the waterways in the Waikato region. The aim of the project was to look for a method that could make use of captured koi carp. Wet rendering and autoclave rendering was examined for producing fish meal and oil under different processing conditions such as time, temperature and water content. The water content of raw minced fish was around 69-77%, the solids content was between 23%-31%. Ash content was 6.2-7.4% of the dry solids and fat content between 13.7%-30%. Fish with a high fat content were females containing roe. The meal produced from wet rendering contained 22-28% solids, with 5-9% ash and 14-16% fat on a dry basis, while the stickwater contained 3% solids and 12-39% ash on a dry basis. Autoclave rendering produced a meal containing 26-30% solids, 3-5% ash and 30-31% fat on a dry basis and a stickwater containing 3.2% solids and 27-32% ash on a dry basis. Fat reduction in meal increased with rendering time for wet rendering up to 30% at 40 minutes rendering time, while only a 20% reduction in fat was achieved for autoclave rendering. Wet rendering was selected for producing meals. Dry pet food and wet pet food was made by mixing rendered fish meal with chicken mince. The dry food was produced by baked while the wet food was produced by steaming. Taste testing showed that cats preferred wet pet food over the dry pet food. The dry pet food had a strong odour and poor palatability. Most cats in the taste testing hesitated to try or eat much of the dry food. It was hard for them to chew the nibbles. Less koi carp meal should be used to improve palatability. The majority of the wet pet food was consumed and it had a better odour. A customer survey showed acceptance of koi carp for pet food was high. 92% of the participants felt they would buy or try later. People who have pets were more open-minded about using pet food made from koi carp. An economic analysis showed that 165 tonnes of koi carp could be harvested per year from four Waikato lakes by Huntly, maintaining a biomass density of 140 kg/hectare, down from the current average density of around 200 kg/hectare. To reduce the density down to 100 kg/hectare, koi carp would need to be harvested at 205 tonnes per year for the first 12 years, reducing harvesting to 170 tonnes per after this. Wet pet food production is much more profitable than dry pet food production. The price of each 100 g can of wet pet food to break even should be around $1.7 which is comparable to supermarket prices. This is approximately 10 times the price of dry pet food on a per kg basis. The profit made at $2 per can at 165 tonnes of fish per year is $408K while at 205 tonnes of koi carp the profit is $526K. Dry pet food needs to be sold at just under $6 per kg to breakeven at 165 tonnes of koi carp per year. This decreases with increased harvesting to $5 per kg at 205 tonnes of koi carp per year. If the sales price of the dry pet food is $8/kg, the profit obtained processing 165 tonnes of fish per year is $52K, while at 205 tonnes per year, it is $83K. Dry pet food at the supermarket retails for $5 to $15 per kg.
Type of thesis
Wei, J. (2020). Rendering koi carp and creating economic value by making pet food (Thesis, Master of Engineering (ME)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/13803
The University of Waikato
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