Quality begets quality. This axiom can hold true for many things, not the least of which is egg quality. If the objective is high survival from egg to first feeding, preparation is months prior.

It is now well established that brood fish need be on a special diet at least 10 months prior to spawning date. The preferred is 12 months. This has some ramifications that are not immediately apparent.

Sorting Brood

The sorting of brood fish from production fish is commonly at harvest time when the fish are up close and accessible. Some farms sort at grilse grade thinking that the larger percentage of remaining fish will be female (this is not always a sound practice). In both these cases the fish have been on grower diet in the magical period of gamete growth.

The problem of using a grower diet on broodfish is that the fish receive a high- energy ration that is aimed at promoting somatic (body) growth not the growth of gametes. Early brood nutrition is important to the developing gonad and has different fat and protein profiles compared to grower diets. A couple of examples: oils from terrestrial animals are saturated, meaning the carbon chains do not have knots in them; they are relatively lower in energy; they are solid at room temperature. Fish oils are highly unsaturated and are knotted between carbons; they are high in energy; cold water fish don’t form into fishcicles. Protein from grains or non-fish sources may not be complete: they are fine for growing flesh, but not yolk. High quality proteins from fish sources tend to grow fine gametes.

So, if broodstock are selected from harvest or grilse sort, they may not have a good start to producing quality eggs.

The Perfect Brood Diet

What is the perfect brood diet? Generally speaking it should contain oils from fish sources, those that are particularly high in the famed omega – 3 and –6 fatty acids. These are the highly unsaturated fatty acids (HUFA) most often referred to as EPA and DHA. The ratio of the EPA and DHA is also important. These HUFA are important in the construction of new cell walls, embryonic metabolism and the construction of nervous tissue. This is why Mom made you eat cod liver oil every morning. Another reason to appreciate your broodmom.

There is a condition in incubating eggs known as the "pimple". This is a little white disk or zit that develops just under the surface of the egg about 2-3 days post-fertilization. It is indicative of saturated diets in brood diet. Oil from the fish (food or extracted from flesh) is deposited in the egg for energy. If the source of the oil is saturated or unsaturated, it still gets deposited in the egg. The problem is, butter is solid at room temperature and it’s saturated oil. Broodstock are held at higher temperatures than egg incubation. Put the fertilized egg in colder water and watch the pimple form as the saturated oil droplet becomes solid like butter.

Protein sources should also be from quality sources. ‘Balanced’ amino acid diets make sure that no one amino acid dominates the scene and essential amino acids are present. However, no one knows what the optimal mix of proteins is for brood fish. Low temperature manufacturing and quality fishmeal is a safe bet for good diet.

Vitamins and minerals are an important aspect to brood diet except that little research has been done. There are good ideas on things like the type of pigment and levels of selenium, but the profit margin is not there to really investigate further. And who wants to donate their broodstock to a nutrition study?

How much to feed

Now to feeding: Nial Brommage and coworkers (in: Brommage and Roberts, 1995) undertook a ‘when and how much’ to feed study. In this work they fed groups either high or low rations and changed the rates to the opposite prior to spawning. The study went from September to September with the switch in the last summer. For example: a group on low ration was switched to a high ration a few months prior to spawning. Similarly, high was switched to low and every combination in between was tried. The group looked at fecundity (eggs per kilo), fertility and survival.

The results clearly showed that starving fish was not an option. Fish at a low ration and switched to high ration were large, but the fecundity was low. Fish at high ration were large, but fecundity was not the best. The best results in all categories were when the fish were fed a high ration for the first nine months and reduced in ration prior to spawning.

The take home messages: 1) Select broodstock early, 2) Feed a quality broodstock diet for a year prior to spawning and 3) Decrease feeding 1-2 months prior to spawning.

Literature cited:

Brommage, N.R. and Roberts R.J. (eds)1995. Broodstock Management and egg and larval quality. Blackwell Scientific. Oxford England.