3. CONCLUSIONS AND RECOMMENDATIONS

The necessary infrastructure has been set up to enable FARTC to carry out its research programme in carp nutrition. The capability to carry out proximate chemical analysis, basic to diet formulation, is now firmly established at the Centre. This capability will be extended to include analysis of amino acids, vitamins, minerals and energy content of feeds when a full complement of technical staff is reached.

To achieve the objective of making available efficient and economical diets to farmers-engaged in carp polyculture in various parts of the country, a programme for diet development was also started. A physical survey, whereby samples of ingredients suitable for fish feed manufacture were collected, analysed and evaluated, was conducted in Bhubaneswar. At the same time, a literature survey covering the country as a whole was also carried out. In view of the wide variations in quality found among the ingredients surveyed in Bhubaneswar, the physical survey should be extended to the rest of the country. An initial step in this direction was taken when CIFRI substations throughout the country agreed to cooperate in submitting samples, together with economic information, to the Centre for analysis and evaluation. The survey would not be limited to common feed ingredients but would also include unconventional feed materials that can be developed for compound fish feed manufacture. On the basis of more complete information becoming available, appropriate diets can be formulated for testing in the various locations.

Modifications to the current supplementary diet for carp polyculture were made and tests conducted on rohu fingerlings. Initial results indicate improvement of the diet by fortification with vitamins and minerals. More extensive tests involving other species of the polyculture need to be conducted to determine the relative benefits of such a diet. Testing of the diet in pond polyculture is also desirable to determine the relationship between efficacy of feeding the artificial diet and availability of natural foods, especially zoo-plankton in the pond.

Production of water-stable pelleted feed was successfully carried out using kitchen utensils. With the installation of a laboratory pellet mill in the near future, experimental diet-making capability of the laboratory will be enhanced. However, to properly meet future needs of the Centre, provision should be made for the installation of a mill capable of producing up to 1 t/h of dry, pelleted feed. Preparation of fairly large quantities of purified and semi-purified diets in the future for experimental purposes will also require special equipment. Diet manufacturing equipment suggested for purchase is listed in Table 7.

A continuing programme for carp nutrition research at FARTC is recommended. This should focus on two major areas:

1. nutritional requirements of Indian major carps; and

2. practical diets for mono- and polyculture of Indian major carps.

(i) Nutritional Requirements

Studies on nutritional requirements should be aimed at determining specific nutrient requirements with respect to species, age, size, and rearing purposes. Priority should be given to the study of amino acid requirements, and protein-energy relationships.

Amino acid requirements:

Amino acid requirements for growth in individual species of Indian major carps should be studied in the context of satisfying such requirements in practical diets. As such, experimental diets should be the less expensive semi-purified type. Feed ingredients known to be limiting in specific essential amino acids (EAA) should be used in conjunction with synthetic forms of the corresponding EAAs in test diet formulations.

Comparison of post-prandial with fasting plasma amino acid levels provides a good indication as to which amino acid is limiting in the diet. This is based on the premise that amino acids supplied by an ingested protein are removed from the blood at rates proprotional to the animal's requirement for each amino acid. Blood samples sufficient for quantitative amino acid analysis by partition chromotography can be safely and easily obtained from the caudal vein of fish weighing 100 g or more. Care should be taken to prevent haemolysis from occurring in the sampled blood. Heparin, sodium-EDTA, or sodium citrate should be tested to determine the anti-coagulant of choice.

Protein-energy relationship:

Protein-energy relationship in diets for individual species should be studied to determine the optimum ratio of these two nutrients for maximum protein accretion by the fish. Utilization of various forms of carbohydrates, such as raw and cooked starch, by individual species under different temperature regimes should be studied. The protein-sparing effect of dietary carbohydrates can thus be determined for individual species.

(ii) Development of Practical Diets

Development of practical diets should be based on ingredients which are inexpensive and easily obtainable. Although priority should be given to improvement of supplementary diets currently used in the polyculture system, complete diets should also be developed for testing to determine their economic feasibility in monoculture among the respective species. Of particular importance is the development of artificial substitutes for natural live foods for hatchery-rearing of larvae. To obtain a complete list of ingredients suitable for use in diet formulation, the physical survey begun in Bhubaneswar should be continued and extended to cover all regions and include materials which can be developed for this purpose.

A. Larval diets

Recent studies have shown that larval diets which meet both nutritional and feed particle size criteria can be developed from whole chicken egg. Studies have also shown that certain types of food yeasts support high growth and survival rates among larvae of certain species of warmwater fish. Successful development of a universal larval diet based on locally-available feed materials will remove an important constraint for carp polyculture.

Encapsulated whole egg diet

Poultry eggs are readily available in most towns and villages throughout the country. Although expensive and used almost exclusively as food for humans, its cost as a food for fish larvae is probably no higher than that of artemia. Indeed, boiled egg yolk continues to be used as a larval feed by hatcherymen in the country. However, there are problems associated with its usage. Growth response to egg yolk appears to be far inferior to live natural food, possibly due to its protein-energy imbalance and to its deficiency in certain vitamins and minerals. Moreover, its usage often results in high mortality among fish larvae due to fungal infection arising from deteriorating water quality.

Recently, an encapsulated diet was developed based on the use of whole egg. This novel diet provides a better nutrient balance while at the same time produces no adverse effect on water quality. Most important, each diet particle has the same nutrient balance as the whole egg. Preparation of this diet is simple and, on a small scale, can be carried out with simple kitchen utensils. Further development of this diet is necessary to further improve its nutritional value and handling properties.

Torula yeast (Candida utilis)

Pasteurized torula yeast has long been recognized as a valuable feed ingredient for poultry and livestock. It is produced from molasses, a by-product of the sugar refining industry, available cheaply and in abundance in the country. Feed-grade torula yeast is much less expensive than artemia as a food for fish larvae.

Tests should be carried out to determine the efficacy of dried, pasteurized, as well as live, torula yeast in terms of larval growth and survival.

B. Complete balanced diets

Development of complete practical diets for growth among individual species of the polyculture is desirable from two standpoints. Intensive monoculture with complete feeding of species such as the rohu and catla may, in some areas, be highly feasible economically. Efficient, balanced diets will then be required. Second, evaluation of new feed resources can only be accomplished through tests involving the new feed materials as components in balanced diets.

Development of complete diets should, therefore, be aimed at achieving high feed efficiency at low feed cost. To accomplish this, application of knowledge gained in studies on nutrient requirements plus knowledge acquired on optimum feed particle size for different age/size fish and optimal feeding rates and frequency will also be necessary. Methods for dispensing dry as well as moist pelleted feed should also be studied.

C. Supplementary feeds

Although considered essential for increased fish production in the polyculture system, supplementary feeding is not without problems. Depending upon the natural fertility of the pond, species mix, and type and quantity of feed given, supplementary feeding may be inadequate under one set of conditions while excessive and wasteful in another.

To prevent the possibility of nutrient imbalance in the overall diet of those species in the polyculture expected to benefit most from such feeding, supplementary feeds should be well balanced with respect to nutrients. In fact, the safest and probably most efficient type of supplementary feed should be similar to feeds used in full feeding. The difference need only be the quantity of feed given. The development of supplementary feeding should, therefore, aim at establishing proper feeding rates and frequencies for maximum efficiency under changing conditions mentioned above. As in the case of complete feeds, methods for dispensing supplementary feeds should also be studied.

Four considerations are relevant to nutrition studies. These are:

1. Experimental design

The design of an experiment should be guided by the following principles:

1. No more than two experimental questions should be asked of one experimental design;

2. The number of replicates should depend on the expected degree of difference between treatments, with at least one replicate for each treatment group;

3. Except in comparative feeding trials test diets should be compared against a control diet containing all known nutrient requirements of species. The experimental diet should be different from the control in only one factor, and no change should be made of diets during the course of the experiment;

4. A feeding schedule, based upon age, size of stock and physical parameters such as water temperature and dissolved oxygen levels, should be established;

5. Proximate analysis should be conducted on all test diets (including control diets where applicable);

6. The experimental period will depend upon the experimental question asked. For most growth studies involving fry or fingerlings in aquaria, a 90-day period is often adequate.

For statistical considerations, three experimental designs are applicable to studies in fish nutrition:

1. The completely randomized design, for homogenous experimental units;

2. The randomized complete block, when there is no homogeneity in one direction;

3. The Latin square, when the replicate units are randomly assigned, such as in studies conducted in sectioned-off raceways or in ponds arranged in a matrix.

In nutrition studies involving diet treatments, experiments are often conducted on the premise that if the test animals in the experimental groups are balanced with respect to age (or size), or sex, these causes of variation balance out and do not affect the outcome of the experiment, and whatever differences may be observed are due to the differences in treatment alone. However, the possibility of one or more of these variables having an effect on response to the diet treatment makes the separation or “factoring” of these variables for statistical analysis highly desirable. An experiment which lends itself to such an analysis is known as a factorial experiment. This is the most common statistical approach in nutrition studies. A highly simplified example of such a factorially-designed experiment is given in the Appendix.

2. Experimental parameters

Experimental parameters needing description are:

1. Location of experiment (whether indoors or outdoors) and a description of the environmental conditions, such as light and temperature regimes, as well as chemical parameters;

2. Number of fish in each container - depending upon the size of the container and the age and size uniformity of the animals experimented, from as few as 10 to as many as 500 fish may be placed in each container. Increasing the number of replicate containers (e.g., in a wet laboratory) may substitute for high numbers of fish in each container;

3. Fish should be graded to ensure minimum size variations;

4. Fish from a single family or from many families may be used, but this must be stated;

5. Stocking density should be consistent with size of the fish, type of enclosure, and as far as possible, relevant to commercial practice;

6. The ration, frequency of feeding, and feeding methodology (such as external stimuli to warn the fish of impending feed) should be described;

7. Fish lost through escape, death, or to predators, must be recorded.

3. Data collection and analysis

Growth, feed intake and feed conversion values form the bulk of the data collected in nutritional studies. Sometimes, proximate analysis of the experimental animals is also desirable.

1. Growth is measured as weight gain at the end of the experiment. This is either expressed as percentage of body weight, or as percentage of body weight per unit of time. Although body length measurement by itself is seldom used as a measure of growth, such measurements are recommended at least at the start and at the end of the experiment for determination of the condition factor, k

   

2. Feed intake must be recorded for the experimental period and for each sub-period (if applicable). The quantity of ration may have to be altered to take into account stock loss;

3. Feed conversion is the most commonly used measure of feed efficiency and is expressed as amount of feed consumed per unit weight (wet) gain. Protein efficiency ratio (PER) gives an indication of protein value of the diet and is expressed as weight gain per unit protein intake. Cost parameters have limited value except in comparative feeding trials involving practical diets, and may be expressed as the cost of feed/1 kg gain;

4. Proximate analysis of small numbers of fish (whole ground) before and after the experimental period provides useful information relating increments of body constituents to intake of dietary constituents.

4. Interpretation of results

Since the interpretation of results of an experiment is based on statistical analysis of data collected, a proper choice of experimental design facilitates the process.

Table 1

EQUIPMENT INSTALLED IN FARTC's NEW NUTRITION LABORATORY

Table 2

PROXIMATE ANALYSIS OF FEEDSTUFFS COMMONLY AVAILABLE IN ORISSA STATE ¹

¹ Analyses were carried out by counterpart staff at the newly established Nutrition Laboratory, FARTC, during the period of the consultancy

² Nitrogen-free extract (obtained by difference)

NA Prices not available

Table 3

INDIAN FEEDSTUFFS SUITABLE FOR FISH FEED

¹ Percentage dry matter

² Nitrogen-free extract

³ Included in NFE

Sources: Nutritive value of Indian cattle feeds and the feeding of animals. By K. C. Sen, S. N. Ray and S. K. Ranjhan, ICAR, New Delhi, 1978, and Joint Publications, Commonwealth Agriculture Bureau, No.10, London, 1947

Table 4

TEST DIETS FOR ROHU FINGERLINGS

¹ Diets were made into dry pellets as described in the text. All diets presently under testing, with the exception of Diet No. 5. Feeding trials conducted in 3 ft Æ plastic pools placed indoors with water depth of 10 in. Duplicate pools for each treatment with 10 fish per pool (average group weight, 38 g). Pools are continuously aerated using a common air-line, maintaining 7–7.5 ppm dissolved oxygen monitored by Beckman II system with recorder attachment. Indoor water temperature in February ranged between 24–28°C. Water change is carried out once every other day. Diet No. 5 was not tested due to shortage of sesame oil cake at the time of diet preparation.

² Trace mineral mix made from CuSO₄.5H₂O, FeSO₄.7H₂O, MnSO₄.H₂O, ZnO, CoCl₂.6H₂O, Kl and CaHPO₄ (filler) to provide the following (ppm total diet): Cu, 10; Fe, 100; Mn, 50; Zn, 50; Co, 0.05; and I, 0.1.

³ Vitamin mixture to provide the following (per kg total diet):
Vitamin A, 5 000 IU; vitamin D, 600 IU; thiamin, 10 mg; riboflavin, 20 mg; pantothenic acid, 30 mg; niacin, 50 mg; and ascorbic acid, 200 mg. Due to the unavailability of individual vitamins at the time of diet preparation, Miles Brand multivitamin tablets were used at the level of 1 tablet/kg diet.

Table 5

RECOMMENDED TEST DIETS FOR CARP FRY

¹ Test diets to be made into dry pellets as described in text. Pellets should be ground to particle size not larger than 0.5 mm

² As in Table 4

³ As in Table 4

⁴ Estimated cost: I.Rs. 50/kg

Table 6

RECOMMENDED TEST DIETS FOR CARP BROOD STOCK

¹ Test diets to be made into dry pellets as described in text

² No data available on lysine and sulphur amino acid content

³ As in Table 4

⁴ As in Table 4

Table 7

EQUIPMENT LIST FOR A 1-t/h PELLET MILL

¹ Estimated dockside prices quoted in mid-1980 by one US manufacturer. All items except the pelleting system can be fabricated in India.

² Excluding boiler cost