The natural environment of New Zealand is a highly cherished and important factor of the country. Introduced koi carp is considered a pest in New Zealand because it has a deleterious effect on fresh water systems. Hence eradicating the fish is essential. Identifying possible uses for this captured fish will help offset the cost of eradication. The aim of the study was to identify feasible products that could use koi carp as a raw material without the added impediment that a long term stable supply would not exist once fish numbers had been drastically reduced. The applications identified from a literature search could be categorized into three main groups: as food (for example canned carp); processed non-food uses (for example extracting fish collagen); and miscellaneous applications (such as biofertilizer). Silage production is a simple and cost effective method for using whole koi carp. The process involves mixing thawed minced fish with an acid and keeping it at a particular temperature for a short time. The effect of stirring conditions, pH and temperature was determined in the preliminary laboratory trials. A good silage requires a constant pH between 3.5 and 4.0 throughout the process and needed to be kept at 40°C for four days. Throughout the process the mixture needs to be thoroughly mixed. The main trials investigated the effect of different mineral and organic acids (singly and in combination) and the effect of using kiwifruit pulp as a source of proteolytic enzymes. The combination of hydrochloric acid and acetic acid (50:50 v/v) gave the best silage with high soluble solids content. Adding kiwifruit gave higher soluble solids after 36 h but the proteolytic activity then stopped. The process may need daily additions of green kiwifruit pulp to obtain a good silage. It is recommended that further studies on the biochemical changes during the silage process, the effect of other acid combinations in different proportions, the effect of acid strength, and other sources of exogenous proteolytic enzymes be investigated. It is also recommended that the costs of a commercial process be determined.
