GuppyLabs - Guppy Nutrition

By Sergio Chaim

Guppy Nutrition - Part 1

Energy, Protein and Amino Acids.

I am not intended to re-invent the wheel so I strongly suggest you read the articles I cite under further reading topic, placed below, for an introduction to fish nutrition.

Right now is agreed among researchers that fishes have nutritional requirements for energy, protein and animo acids, lipids and fatty acids, minerals and vitamins.

At this Part 1 I'll freak out through the informations I gathered, and my personal thoughts (*_*)..., on nutritional requirements of guppies for energy, protein and amoni acids.

Energy.

As far as I understand this whole stuff the first nutritional requirement of any animal is to satisfy its energy needs. If we supply it with enought energy it will stay alive, possibily with no growth, perhaps with some weight loss, or even no reproduction, but yet alive.

The gross energy content of foods and feddstuffs is determined in laboratories mensuring the amount of heat released by a sample during its complete combustion.

Unfortunately I never saw in any ornamental fish food pack any direction about its energy content so I use a trick to figure their gross energy content. The trick is multiply amount of feed fractions which works as energy sources (protein, fat and carbohydrates) for their mean values of heat combustion, 5.64, 9.44 and 4.11 kcal/g.

If you are thinking in pure animal origin foods/feedstuffs (animal meals, live food and some animal origin ingredients used in pastes) you should do not take into account their carbohydrate content, well, if they were not adultered..., because animals do not store significant amounts of carbohydrates. As far as I remember animals only store some glycogen in the liver and some few glucose, both in neglegible amounts.

On the other hand while thinking in manufacturated fish foods, which usualy contains plenty carbohydrate rich vegetal matter, and vegetable origin feedstuffs we have to use a second trick to figure a fraction called "nitrogen free extract", that is not clearly cited in labels too and whicht could be taken as its carbohydrate content. This way you subtract from 100% the amounts of protein, fat, fiber and ash and the leftover is assumed to be the nitrogen free extract or carbohydrates. Of couse this fraction will also contain a lot of errors from analytical methods applied in the deternination of former fractions...

From a nutritionist view point the gross energy content is not the best way to judge the energetic value of a food or feedstuff because many losses occurs during digestion and absorption processes as excretory and heat losses. So researchers prefer talk in terms of digestible energy requirement in order to discount fecal energy loss that is the most significant excretory loss and the one mostly effected by feed quality and/or type . They could also use metabolizable energy form like made for most species of land animals but the deternination of these values for fishes represents a chalenge in the sense that the metodology available today is too stressing for fishes, several times producing doubtfull data

Figure 1 - Schematic presentation of the fate of dietary energy for fish, categorizing the losses that occur as feed is digested and metabolized, leaving a fraction of the energy to be retained as new tissue. Source: Adapted from National Research Council. 1981. Nutritional Energetics of Domestic Animals and Glossary of Energy Terms. Washington, D.C.: National Academy Press. From NRC (1993), pp 3.

About "feed quality" I have to say that vegetables which enclose nutrirents inside fibrous walls are not well digested, usually fiber is not digestible, broke. Fish meals produced with by-products of fish processing industry, usually containing too much scales, bones, viscera, and another non digestible thinks, so called white fish meal, is not as well digested as darker ones which get this darker color due presence of higher amounts of highly digestible fish flesh. A very long time ago I read anywhere that Dr. Jim Alderson recommended to avoid feed guppies with fish meals produced from freshwater fishes due intrinsic sanitary risks, I personaly would be even more concerned if the fish meal were produced from visceras and its content, s#$%... Crustacean meals is another dificult by product, usually it contains a lot of carapaces, chitin that is indigestible for itself, but it also contain a substance called chitosan that, as far I know, when weted forms a gel in digestive tube, this gel at least binds fat, may be it binds carbohydrates and proteins too, preventing their absorption. In short all these non digestible feeds usually produces relatively high amounts of mineral matter, nickname in labels is ash, them in some sense we can see ash content of feeds as an indicator of their quality.

Fishes take relatively more energy from protein metabolism than mammals and birds because they readly excret ammonia in the water instead wasting energy to produce uric acid and urea as by product of protein catabolism. Togheter with our almost complete unknowledge of ornamental fish nutritional requirements for proteins and amino acids this can explain why ornamental fish feeds have so high protein levels, the fishes could switch the use of protein for energy or amino acids supply, an wild card. Well, since protein is the most expensive fraction of a diet, that it is potentialy the most poluting feed fraction and that there is a sparing effect of energy level in diet on protein requirements the main concern of food fish nutritionists is express energy requirements based on the protein content of diets looking for the minimal protein level required to sustain maximum growth. This way researchers determined that ratios of protein to energy (mg/kcal) for maximum weight gain range from 81 to 117 mg of digestible protein per kcal of digestible energy.

Usually feed intake is ruled by the satisfaction of energetic needs, I mean animals eat until their brain say they thats enought. If a diet is relatively high in energy may be the fish will not take all the protein, and other nutrients, it needs. When diet energy is yet higher the fish will take much more energy before the brain sign to stop feeding allowing the deposition of body fat. On the hand if energy is relatively low the fish will waste protein to satisfy its energy needs.

As far as I know only Fah & Leng (1986) gave us some light on the energy requeriments of guppies.Frankly speaking I do not know or where they got data for metabilizable energy of experimental diets. They do not make reference to any data source and they do not clearly state that they performed such determinations. I think they simply "adapted" data determined for another species or there was a typing error. Anyway Sales and Janssens (2003) concluded: "The protein requirements of these juvenile omnivorous (guppy, goldfish, tin foil barb), carnivorous (discus) and herbivorous (redheaded cichlid) ornamental fish species are in accordance with requirements reported for food fishes (NRC, 1993).".

Table 1 - Protein:Energy ratios recommended for different fishes species. Adapted from Fah & Leng (1986) Tables 1 and 2, Sales and Janssens (2003) Table 1 and NRC (1993) Table 7-1.