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Discussion Starter · #1 ·
Choosing foods based on calorific values

I’ve had this odd idea bouncing around in my head for quite a while now about calories and wonder weather fish look at this as well, maybe not to the same degree that we humans do, but none the less is it possible.

fish can be opportunist when feeding, we know this because of the variety of food item’s found in there stomach content’s etc, but do they have a preferred food over another when available and if so, why ?.

if they do have a preference, is this chosen on the easy availability of forage at that time of year or is it based on something else like calorific value of said forage.

it’s a question that I find very interesting and also very complex.

So out of all there available food sources which ones have the highest or lowest amount of calories per gram and where do they sit in the glycemic index.

The more calories and a lower G.I a food item has the less time a fish needs to hunt for more, so this in turn uses less energy, on the other hand when they can only eat low calorie foods with a high G.I it may use more energy than it receives from what it’s eating, making it use up vital fat reserves to survive.

The fishy menu,

how can we find out what calories etc are in the food items that our fish eat, the only way I can see is by lots of scientific research by us, which will take time, I mean how do you find out just how much energy, fat, carbs, protein etc, is in a 2 oz hard back crab or a 3” long prawn, a small wrasse or a 6” sand eel, does it really matter I hear you say, I don’t know, they maybe just the rambling of a crazy man that can’t seem to get the idea out of his head, if I knew all the above information I’d feel that it would be another part of the jigsaw puzzle that I’ll be able to put in place though.

All of this may mean nothing, but then again it could be a major key to being able to know what should be there preferred forage at any given time of year, this information then can be used to improve our knowledge over lure choice and presentation techniques, a little food for thought maybe ?

kev
 

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I tend to believe in the inbuilt predator instinct - Bass would hopefully choose a big slow bait over a small fast one - the energy gained vs energy expended ... all hypothesis of course :D if that was the case they would never take a lump of plastic with hooks!
 

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Do Bass learn ?

Calorific value ? I don't know.

I think Bass have instinct for what is good and what is bad just like we do. We get those gut feelings and I'm sure that left out in the wild long enough, we'd learn to pick the good from the bad whilst instinctively leaving other stuff well alone. I think this is why we have inbuilt fears of certain creatures and stuff.

But, a returned Bass ?

Different story. I reckon they do learn given the opportunity.

Bass also travel great distances sometimes and, I think we often forget, they experience, or can experience forage far more wide ranging than available locally.
 

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Not sure about bass, but White Sharks do. I remember watching somethin on Discovery a while back and the white sharks they studied would attack most things but let go as soon as they realised it wasn't what they wanted through sensory glands in the mouth or soemthing, hence most human attacks are single bites, grab a leg, they sense not much blubber on it and let go. Nice juicy seal, loads of blubber, yummy.
 

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What you are talking about here, is Optomal Foraging Theory (OFT). the principles of this theory is that organisms
focus on consuming the most energy whilst expending the least amount of energy, based on the assumption that decisions
made when forageing maximise the net rate of energy gain.

before you can determine the amount of energy gained by the consumption of one prey item, there are a few factors
that must be considered:

-The time it takes for a fish to search for food.

-The time it takes to persue capture and eat a prey item.

-Nutritional value, and digestibility of prey.

-Defence, and anti-predation mecanisms of prey.

and many more.


To answer your question can you determine the Calorific Value of each prey item?

Yes, fairly easily, with a good knowlege of nutrition and chemistry, and a good lab.
But it is very difficult to determine the actual energy gain that a fish gets from consuming a particular food source
without knowing all of the factors which have determined the choice of prey.

I hope this helps, can forward you many references if you wish to read more about this.


Gareth
 

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Interesting!
For them to choose what they eat, there would have to be a choice. Do the bass we catch feel like they are stuffed full of anything or is there still room for more food in there. Do they make a conscious choice or it is just what is in front of them?
I could believe that they follow seasonal trends in their feeding pattern, availability would dictate that. Apparently our brains can tell us unconsciously that we need certain food types or components like salt,perhaps fish have the same sense. If they are lacking in minerals (not salt obviously!) do they target certain food types? If so, how often and for how long?
As for whether it would change how I fish in order to target certain food types, other than seasonal variations I doubt it but I will reserve judgement for now.....
 

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Discussion Starter · #7 ·
What you are talking about here, is Optomal Foraging Theory (OFT). the principles of this theory is that organisms
focus on consuming the most energy whilst expending the least amount of energy, based on the assumption that decisions
made when forageing maximise the net rate of energy gain.

before you can determine the amount of energy gained by the consumption of one prey item, there are a few factors
that must be considered:

-The time it takes for a fish to search for food.

-The time it takes to persue capture and eat a prey item.

-Nutritional value, and digestibility of prey.

-Defence, and anti-predation mecanisms of prey.

and many more.


To answer your question can you determine the Calorific Value of each prey item?

Yes, fairly easily, with a good knowlege of nutrition and chemistry, and a good lab.
But it is very difficult to determine the actual energy gain that a fish gets from consuming a particular food source
without knowing all of the factors which have determined the choice of prey.

I hope this helps, can forward you many references if you wish to read more about this.


Gareth
thanks gaz, i think any info relavent would be helpful, i'd like to have answers like how many calories does a 5lb fish require a day/week to sustain it's weight or increase/lose, i think the more know about your target fish and forage of said fish can only help in hunting it down.

P.S it's amazing how everyone as focused on bass, when it wasn't even mentioned in the first place, strange that.
 

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i'd like to have answers like how many calories does a 5lb fish require a day/week to sustain it's weight or increase/lose,
The sort of figures that you are after have been calculated for some species of fish, as they are used to formulate feeds for farmed fish. The problem is that the metabolic rate and energy budgets of fishes determined in controlled lab conditions may not represent those of wild fish due to a wide variety of factors that determine these. for example, metabolism will be effected by parameters such as; temperature, activity, age, reproductive status etc.

Gareth
 

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I'm sure there's something in this idea although there will always be exceptions. Predatory animals will choose an easy meal over a hard one and a larger one over a small one. I'm not sure that they go so deep as calorific content but clearly a pike will eat a dying 6" roach rather than chase a shoal of 1" fry. Sometimes though they will get so keyed on to a prevalence of prey items that they will lock out the detection of other foods that may pass them by. There have been times when pike fishing when the pike fixate completely on 3" fry and will not look at a 7" lure that passes them by. Because they are hunting the small fry so hard they just can't carry two "prey images" at the same time. There's an excellent book about this theory by Bob Wyatt called "Trout Hunting". Granted its about trout but the ideas he presents are very transferable to lure fishing.

Another example of this singular prey image fixation is shoals of busting tuna. There are times when they are locked on to 3" sardines and will not touch anything bigger. You would look at the foam and leaping fish and imagine they would eat anything you throw at them but not so. Even if that lure or bait you cast would represent a bigger meal.
 

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Keith,
I think you may be on to something. What does make nay fish move an area and concentrate on one particular prey item??
While we know several species of fish that do take advantage of seasonal gluts of food-trout and mayflies for example. Large prey item, taken with little effort-high calorie/low effort.
While I think these "easier" sources of food do effect the movements of any predator, I think most (if not all) predators will remain open for any prey item, that crosses it's senses. The urge to chase is a powerful trigger. If we can identify the better (for the predator) food items, that would give us a powerful tool in locating them.
I my local area, most bass seem to favour crabs, even fish taken on clean ground will often have crabs in their stomachs. So they are searching them out/or finding them easier than the Sandeels that also frequent the clean ground.
 

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There was a program on last night which showed an interesting test - on humans though.

A guy was placed in an MRI scanner while being fed different solutions fat. One was 5%, one 10% and the last 30% fat.

They monitored his brain activity for each one and found that brain activity was significantly increased by the 30% and less so by the 10% when compared to 5% solution.

The 30% actually engaged the part of his brain associated with movement as well as reward.

If this translates to fish, the bait that contains most fat, should in theory be the preferred food - although this is assuming each is equally easy/difficult to catch and the fish recognises the difference.

Maybe we need to run a test on captive bass.... give them the option of each type of food and see what they prefer :-D
 

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P.S it's amazing how everyone as focused on bass, when it wasn't even mentioned in the first place, strange that.
That's my fault.

I used Bass in my initial reply basically because, we seem to know more about the commercially viable species than all the rest.
I figured that any research would have most likely targeted Bass, Cod, etc
 

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I think it is too easy to focus 100% on energy.

Energy will be near the top of the list at all times but fish need a balance in their diet just like anything else. Essential vitamins / minerals / amino acids will always need to be found. I'm not sure fish trust to luck on this.
Horses / cows / sheep will happily lick away at a salt block which contains pretty much no energy when there is plenty of energy rich food - why not similar habits in fish?
A spawning female may well have different requirements to a young non spawning male - food decisions may well be taken accordingly.

Variety is the spice of life....

When we go 'lure' fishing what % of takes are based on the fish wanting to eat the lure? How many takes are just an aggresive response?
 
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