The way fish diets have changed

19-10-2016 | |
The way fish diets have changed
The way fish diets have changed

It’s a given that fish health and fish nutrition are linked. As are fish health and environmental conditions. As are fish health and husbandry routines, and genetics for that matter. But let’s look at fish diets and their changing composition.


In business there’s a drive to make a profit; to make a profit by either increasing margins, increasing productivity or reducing costs. Ideally, by all 3. The biggest single expense item, and a prime target for budget pruning – is obviously feed. However, 2 questions arise:

  1. Are we compromising productivity – and jeopardizing our businesses – in striving for lowest cost diets?
  2. And are we losing the very thing we tout as an advantage in choosing fish over terrestrial animals as a protein source?

Fish health and inadequate nutrition

Health issues seem to be springing up around the planet. True, many are dominated by environmental issues, but to what degree is the fishes’ immune system compromised by inadequate nutrition?

Natural species specific diet v cheap and convenient

The premise I’d like to propose was actually raised in conversation with Bill Wiadrowski of Natural Balance Pet Foods. Over the years Bill has designed highly efficient diets for eels, barramundi, silver & jade perch, and Murray cod. He proposes that when natural, species specific ingredients – such as fishmeal & fish oil – are replaced by cheaper, or more conveniently available, non-species specific components, general health diminishes.

Because of the range and degree of other limiting or stock-threatening factors, it’s difficult to quantify the actual degree to which the immune system is compromised by a diet made up of ingredients that the fish wouldn’t naturally encounter in their natural state, it’s at least one that can be rectified fairly easily.

Finding substitutes for fishmeal

The issues driving the trend are of course worthy ones: non-reliance on a finite resource; lowering staple food production costs; recycling of by-products from other food sectors.

Fishmeal is most certainly a finite, and let’s face it, an endangered resource. The same environmental factors that plague open system aquaculture endanger the wild harvest of fishmeal species. The rush to find substitutes in respect of this is commendable, but from Bill’s observations, since the experiments with vegetable oils & proteins, terrestrial animal proteins, and such delights as feather meal, the general health of fish has diminished. This is especially so in the case of high order predators such as salmonids, and some of the pioneer aquaculture candidates such as kingfish.

The financial driving force

To produce a low cost diet only escalates the shortcomings of the above supply driven strategy, but leans more toward an outright dollar saving goal than a balanced nutrition without loss of productivity.

The real question is what is the long term viability of such an approach, and with the added pressure of extreme weather events and long term climatic shift, what steps is the industry taking to cope?

Fish don’t make omega-3 – they store it

The second question raised – the altered nutrient profile of the finished product – hinges on the fact that fish don’t make long chain fatty acids, omega-3 included; they store it. Some fish store more than others. If the ingredients of the rations they’re fed don’t contain them, they can’t store them. This has been demonstrated on more than one occasion when fish tested while being fed on a diet of aquatic-based ingredients, including fish oil and fish meal, gave a high reading, however, when tested subsequently, while fed on a diet of alternative, terrestrial-based ingredients, such as soymeal, were unable to reach the same high levels. The search for a viable fishmeal & fish oil replacement, like the search for the holy grail, is ongoing. The outcomes thus far have been as equally frustrating.

Another step in seeking resolution in this situation could be to bring the farms on-shore into recirculating aquaculture systems. That would at least eliminate, or at least monitor, water quality & temperature factors as culprits. And it would pinpoint the influence of husbandry practices on productivity. That just leaves nutrition & genetics as limiting factors. I’ll concede that it’s a quantum leap for aquaculture, but one that some growers have already fruitfully explored. And one that we may all have to ponder at some stage.

John Mosig Aquafeed

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