Feed has a critical role to play in improving production efficiency and reducing environmental foot-prints in any aquaculture operation. Lack of knowledge in the use and effectiveness of wide variety of protein sources can be seen as one of the weak links in the nutrition of the target finfish species. Therefore, finding alternative to fishmeal in any carnivore finfish species diet is a step forward in closing the knowledge gap and achieving environmental and economic sustainability in farming the species. Finding suitable fishmeal protein replacement(s) and simultaneously omitting the contributions of other micro-nutrients present in the fishmeal, could be other drawback in including fishmeal alternative ingredient(s) in the diet of carnivore species. The contribution of micronutrients present in fishmeal could be in the area of immune competence, flavour and texture of the final product.
In the light of above the current presentation will use Lates calcarifer as one of the examples of carnivore finfish species, where research target has focused on replacing fishmeal with other locally available ingredients. L. calcarifer also known as barramundi, or Asian sea bass, are catadromous, protandrous hermaphrodites, euryhaline, tropical carnivore species that can be cultured in many environments including freshwater, brackish and marine waters. The species in its various product forms, is one of the most sought after fish as it can be cultured in tanks, ponds and cages.
The Curtin Aquatic Laboratories in Perth, Western Australia has conducted several experiments to investigate the fishmeal replacement values of various ingredients. Some of these ingredients are plant based and some are animal based. Some ingredients were bioprocessed, fermented or treated with bacterial and enzymes with an expectation to improve their replacement efficiencies. Various tools including growth parameters, size-frequency distribution, physiological and immunological parameters have been used to investigate the efficacy of fish meal alternatives in barramundi culture. Some of the alternative ingredients tested so far include Nu ProTM, lupins (various species and types), other legumes (Trifolium glanduliferum and Trigonella balansae), peanuts, Spirulina platensis (SP), tuna hydrolysate (TH), and black soldier fly meal (BSF). Some of the research findings are summarised below:
-The use of NuProTM, an organically certified yeast based protein source as a substitute for fishmeal in barramundi diets, is only economically efficient when the replaced percentage of fishmeal is below 9%. The feed intake and growth performance were improved at 60% replacement of fishmeal by NuProTM. It can be used to replace 15% of the fishmeal in the diet without any adverse biological effect on the fish.
-Replacement of 25% or more of the fishmeal in the diet of juvenile barramundi with either T.balansae or T.glanduliferum results in significant reductions in digestibility, feed efficiency ratio and growth. performance.
-Lactobacillus fermentation can reduce anti-nutritional factors, (phytic acid and tannins), and increased the digestibility of protein, lipid, fibre and phosphorus of sweet lupin and peanut meal.
-Treatment of SP with commercial enzymes, cellulose (Celluclast®1.5L) and proteinase (Alcalase® 2.4L) reduced the peptide sizes, increased the digestibility of protein. However, high inclusion level of SP was not favourable diet for juvenile barramundi as with 20% inclusion level started reduce growth rate.
-The stress resistance of juvenile barramundi increased when they were fed fermented lupin and peanut, and germinated peanut based diets.
-The nitrogen discharge into the rearing environment was reduced when juvenile barramundi fed fermented lupin or peanut meal, or spirulina.
-There is a significant increase in SGR of barramundi if a mixture of already researched ingredients, rather than solo, are used to replace fishmeal.
-Future research directions are focussed on improving gut health by investigating gut microbiome characteristics of the species. BSF has shown promising results.