Larval Feeds Dr. Craig Kasper

Introduction Last time…we spoke about live feeds for larval fish. Most live feeds are preferred over processed diets for many reasons, most involving superior fish performance when on the feeds. If you decide to feed diets which are not live, then you have several choices to make. Today we will consider options to traditional live feeds for larval fish.

Table 1 Composition of (chicken) Egg Whole egg egg white egg yolk Protein, % 48.8 76.9 32.8 Fat, % 43.2 - 62.2 Gross energy, kcal/kg 5 830 3 070 6 910 Metabolizable energy (ME), kcal/kg 4 810 2 533 5 700 ME: protein ratio 9.8 3.3 17.3 Calcium, % 0.2063 0.0427 0.2653 Phosphorus, % 0.873 0.282 1.020

Eggs or Not? Raw egg contains avidin (growth inhibitor) de-activated with heat. Cooking unprocessed egg, however, causes irreversible separation of the two egg fractions, yolk and white, due to denaturation of protein components in both fractions. Blending the two fractions requires binders ($$$).

Is my fish full?? Wolf’s index is usful for some applications, but you have to sacrifice fish to make it work. Sometimes you can just look! 1                                                                                                                                                                       

Feed Training Nearly every larval fish will eat a microorganism, but getting them to take to man-made diets is something else. Some fish don’t care (i.e. channel catfish, convict cichlids) while others won’t eat unless extensive feed training takes place (yellow perch). Other challenges include: confirmation of diet ingestion, feed efficacy, and feeding rates, etc. 1                                                                                                                                                                       

Feed Training continued… Feed training isn’t difficult, but time consuming. The goal is to put as much food in front of the fish’s face as the system can withstand! Start hand feeding as soon as the fish are free swimming if you suspect you’ll be feed training.

Yeast Easy to maintain batches. Good source of protein and complex B vitamins. Sometimes Brewer’s yeast is better, but often more expensive.

Microencapsulated Feeds Designed to deliver the maximal amount of nutrition in the smallest package. Difficult manufacturing process (and you pay for it in the end) due to the grinding process needed to make the starter paste. Capsules actually can interfere with some fish guts and cause problems.

Krill? Not as is (too big), but an excellent attractant!! Can get fish which aren’t eating to start eating. Expensive, but a little goes along way.

Organ and Blood Products Great for flavor. Difficult to get due to “mad cow” prion scare. Might be able to contact a local butcher here. Some dried blood products don’t work as well, due to oxidation.