2. DIETARY/FORMULATION ASPECTS

The general sequence of diet evaluation and development is outlined in Table 1, with composition of appropriate diets listed in subsequent tables. Protocol for modifications is discussed along with observations on animal response. The basic approach was to stimulate fry feeding activity with reduction of mortality during the period following collection at the Bardawil Lagoon. Subsequent formulation changes were affected by availability of ingredients and the need for dietary substitutions based on comparable compositional analysis.

Various prepared formulations, especially flake diets, dry mixes, and an assortment of dietary ingredients were brought to Elat by the Consultant for use in the programme. Flake products, notably those containing shrimp meal, were produced on double-drum dryer equipment at Louisiana State University in Baton Rouge. Such materials have proven to be invaluable in the feeding of young fry and have warranted the inclusion of flake manufacturing equipment in the recommendations of this Consultant.

Sparus auratus wild fry, of 0.3 – 0.6 g size, were tested under intensive culture stocking conditions in a variety of holding tanks at the Elat facility. Feeding and mortality rates were tabulated daily and diets developed were based on observations of animal response.

Due to various hatchery problems, it was not possible to utilize hatchery-reared fry in the experiments or to conduct extensive tests with larval foods, including capsulated and flake-type diets, A limited number of such tests are in progress with the surviving post-hatchery animals. Evaluation of hatchery tests, especially system maintenance aspects, is in progress and will be used in projections for the 1976 – 77 spawning season.

Table 1

SEQUENCE OF DIET DEVELOPMENT FOR Sparus auratus FRY

Initial tests were made of the olfactant or attractant value of various additives to the 1 104 71/76 diet (Table 2). Among others, these additives consisted of fish solubles, fish oil, shrimp meal and shrimp protein concentrate, and a selection of specific chemical olfactants. In addition, freeze-dried shrimp meat was evaluated. These shrimp products were derived from waste products of the Louisiana shrimp industry and will be discussed fully in subsequent formal research communications. A continuing line of cooperation has been established whereby newly developed shrimp dietary products will be shipped to Elat for evaluation.

Striking feeding frenzy was noted on the freeze-dried shrimp meat, indicating a decided attractant effect by shrimp-based materials. This was further supported in related tests in which shrimp meal-fortified diets elicited noteworthy feeding responses. Additional observations indicated the desirability of a soft-textured substrate, especially to avoid “mouth-feel” rejection by the animal, often seen with hard particles. Thus, there is a need for a uniform, or homogeneous, small particle that will rehydrate rapidly, resulting in a soft meat-like texture. As noted, flakes were particularly useful in this regard. Based on these initial observations, it was seen that during the initial 72 hours of fry feeding, application of a shrimp-based food, (i.e., as much as 50 percent shrimp meal or the equivalent of a shrimp flavour concentrate) would be desirable. Furthermore, in all likelihood, the initial “starter” diets must contain a minimum of 50 percent protein and 20 percent lipids. Young fry can be rapidly “trained” to respond to an automatic feeder using flakes or small particles. As discussed subsequently, the node of feeding is correlated with the type of holding container and the specific water-distribution pattern.

It should be noted that a response of marine fish larvae to a shrimplike material is not uncommon and has been reported by other workers. The CNEXO laboratory at Brest, France (Section 7), working on sea-bass larvae (Dicentrarchus labrax), attempted adaptation to pellet formulations using various concentrations of Artemia powder (lyophilized and used as an attractant) compared with a natural food. Incorporation of 10 percent Artemia powder to the pellets appeared to give better results. However, more definitive results were seen in terms of survival. Evidence suggested that comparable growth and survival can be achieved on either living food or on pellets. The optimal diet used contained 52.6 percent protein, 12.8 percent lipid and 9.9 percent salt. The shrimp-fortified diets used at Elat, in all likelihood, simulated the biological/nutritional value of the Artemia, brine shrimp, supplement used by other workers.

The composition of the initial diets used, i.e., 1 102 - 71/76, 1 104 - 71/76 and 1 105 - 71/76 IOLR - 1, is given in Table 2.

Table 2

Composition of Initial Diets

Formulations are based on those originally developed at Louisiana State University (LSU) by the Consultant with subsequent modifications made at Elat in collaboration with Dr G. Kissil Source and availability of all commodities used in diet development have been communicated to Dr. Kissil prior to the initial Elat trip. Continual up-dating of information is in progress.

2.1 DISCUSSION OF VARIOUS DIETS

1 104 - 71/76

This formulation differs from the basic 1 102 - 71/76 preparation in that fish protein concentrate (85 % protein) was substituted for the egg protein concentrate (75 % protein) and rice starch pre-gelatinized starch) is used instead of rice bran. These modifications were effected to produce a more uniform flake product since the egg protein tended to coagulate on the drum surfaces of the double-drum dryer when prepared at LSU. The rice starch, in view of its binding ability, provides a smoother blend and more uniform final flake. One series of flakes was prepared in distilled water, another in shrimp blanching water obtained from the Louisiana shrimp canning industry. This blanch water high in flavour compounds (i.e., glycine, arginine, glutamic acid, and nucleotides) may prove to be particularly attractive to young fry. Comparable evaluation of such materials at research facilities other than Elat will permit improvement of formulation, especially its value as an artificial food source for larval early post-larval fish.

1 105 - 71/76 - IOLR-1

This preparation is based on a modification of 1 104-71/76, using the 1 104 - 71/76 dry mix to which Maine vacuum-dried shrimp meal (at one-third proportion) was added. Final protein percent was calculated at 46 percent. Significant animal response to this formulation using the vacuum-dried shrimp product suggested testing of graded amounts of shrimp meal in the basic formulation. Previous analytical work has shown that this particular meal, from Pandalus borealis, is especially high in lipids (9.2 percent), predominantly triglycerides. . Data from many workers indicate a beneficial role (energy source?) for lipids and fatty acid supplements in aquatic diets. Special attention is being given to the value of polyunsaturated fatty acids, predominantly of the w 3, linolenic acid, series. Specific requirements for linolenic acid have been shown.

1 105 - 71/76 - IOLR-2-3-4

These diets, with graded amounts of Maine shrimp meal, are all based on IOLR stock ingredients along with particular items from Louisiana State University. In general, little difference in gross response was observed between the three levels of shrimp meal examined. Formulations are given in Table 3.

Table 3

Formulation of Diets 1105-71/76-IOLR-2,3,4

¹ IOLR products

1 105 - 71/76 - IOLR - 5

Based on the graded shrimp meal tests, a shrimp meal concentration of 25 percent was selected, with fish oil addition increased to four percent, giving a final protein level of 48.33 percent and a percent fat of 9.3 percent (Table 4).

Table 4

Composition of Diet 1105-71/76-IOLR-5

¹ IOLR products

B - IM 74/76

This is the initial formula developed for fry without shrimp meal (replaced with ten percent soya meal and ten percent brewers yeast), using fish oil at six percent and IOLR vitamin and mineral premixes (Table 5), Final protein concentration is 46.9 percent (37.9 percent animal protein and nine percent plant protein). It should be noted that shrimp meal is unavailable in Israel and must be imported from the Scandinavian area or the United States. Thus, it probably can only be used in early fry diets, where volume is minimal, or as an attractant to stimulate feeding and adaptation to increasing reduced levels of shrimp meal in the fry diet.

Table 5

Composition of Fry Diet B-1M 74/76

¹ IOLR products

Diet B + IM 74/76 was prepared and delivered to the fry in the form of patties, on screens and as dry crumbles. The diet was generally acceptable but elicited a minimal response from newly arrived wild fry. It should be noted that fish meal for this and subsequent diets was finely ground since the original meal was coarse, with irregular particles, resulting in a considerable rejection of substrates by the fish following initial ingestion. A feeding frenzy was common upon introduction of the patties into the tanks, but presentation of food in this manner is wasteful. Furthermore, distribution throughout the tank was not possible. It was recognized that a light particle adapted to an automatic feeder would be superior.

B - IM - 2 74/76

This diet (Table 6) contains protein of 100 percent animal origin, has the soya protein and brewers yeast replaced with fish protein sources, and uses a pregelatinized starch in place of wheat flour. This allows removal of the alginate/sequestrant vehicle as a binding agent. While the alginate is an excellent diet binder, it is expensive and unavailable in Israel, both factors warranting its replacement. Certain items can be readily used in small lots of experimental diets, but any projection into large volumes necessitates careful evaluation of commodity availability over an extended time period. The presence of solubles and fish hydrolysate, each at five percent, gives additional chemotactic value as well as providing possible required fish growth factors and feeding stimuli.

Table 6

Composition of Fry Diet B-1M-2 74/76¹

¹ Protein percent calculated at 47.9%.

² IOLR products.

Experimental fry diets based on variations of B - IM - 2 74/76 are discussed in the following section.

Fry Diet Preparation Procedure

The current procedure in preparation of diets for S. auratus fry is as follows:

A considerable loss of Material occurs in the grinding process, resulting in an excessive amount of “fines”. An example is seen in treatment of 350 g of dried material through the coarse setting on the grinder.

Approximately 10 % (33 g) is lost in the processing operation. The size range currently used for <0.5 g size fry is the 500 – 1 000μ particle, thus nearly 50 % of the material (that in the < 500 μ size range) is “lost”. However, the latter fine particles may be useful in the early post-hatchery stages of development. It was calculated that approximately 800 g food are needed to produce 160 g of 500 – 1 000 μ particles. This latter amount was that calculated to be required per day for stock fry with supplementation of 100 g of the flake diet 1 104 71/76. Further estimates indicated a requirement of ca 10 kg of food for a 20 day period to maintain a fry population of ca 16 000 animals.

Problems in preparation of an adequate supply of dietary material for young fry are noted and attention must be directed to resolve the processing limitations. Recommendations are given in a subsequent section of this report.

Analyses of fry diet preparation at the CNEXO laboratories at Brest, Prance, by Dr. Meyers have indicated various improvements in the procedures used at Elat. The essential component of the Brest diet manufacturing process is a micro-mill pelletting apparatus capable of producing particles of 1 mm diameter. A grinding attachment on a food/dough mixer permits further production of fine particles (<1 mm diameter) in conjunction with a sieving operation.