Felicitas P. Pascual

Midgut gland as monitor organ for the nutritional value of diets in Penaeus monodon (Decapoda)

Midgut gland cells of Penaeus monodon postlarvae were investigated by electron microscopy after starvation and refeeding with different diets. Well nourished postlarvae could be starved for 5 days without irreversible detriment. They recovered easily on a good diet. Only R cells were affected by a short starvation period. After 13 days of food deprivation the structures of all cell types were disintegrated. The postlarvae were able to starve for a maximum of 15 days. The most diversified ultrastructure was obtained by refeeding with cod liver oil and 2s (mixed diet). Casein was not well utilized. Sucrose was the poorest diet. The midgut gland of Penaeus monodon seems to be lipid oriented. Only fat was used as storage material; glycogen was lacking. Different ultrastructures were induced in R cells by a given diet after longer starvation periods. The reestablishment of their ultrastructure by means of a definite diet seems to be impossible after a certain period of starvation (point of no return). R cells are very sensitive to different diets. B cells show slight reactions, while F and E cells remain relatively unchanged. This indicates that R cells could be used to monitor the nutritional value of prawn diets in aquaculture.

Carbohydrate requirements of Penaeus monodon (Fabricius) juveniles.

Abstract P. monodon juveniles with an initial mean weight of 0.62 g were fed isonitrogenous (45%) and isolipidic (10%) semi-purified diets containing 10, 20 and 30% trehalose, sucrose and glucose for 56 days. Shrimp fed the diet with 20% trehalose had the highest weight gain. Of the three types of sugar tested, shrimp fed diets containing trehalose and sucrose exhibited better weight gains than those fed glucose diets. A dietary sugar level of 20% resulted in the best weight gain whereas the 30% level gave the lowest weight gain. The survival of shrimp was also affected by the type of carbohydrate fed. Trehalose and sucrose diets promoted higher survival rates than glucose diets. The different types and levels of carbohydrates showed combined effects on the dry matter percentages of crude protein and total lipid. Trehalose and sucrose diets generally promoted increased protein deposition. Trehalose at 30% and sucrose at 20% depressed lipid content.

A preliminary study on the protein requirements of Chanos chanos (Forskal) fry in a controlled environment

Milkfish (Chanos chanos) fry with an average weight of 40 mg per fish were stocked in 60-l wooden-glass aquaria filled with 30 l of filtered sea water with a salinity of 32–34 p.p.t. and a temperature of 25–28°C. They were fed diets containing 20, 30, 40, 50 and 60% protein and 2740 kcal of digestible energy per kg at a daily rate of 10% of the biomass for a period of 30 days. Fish which were fed the diet containing 40% protein had the highest weight gain which was significantly higher (P < 0.05) than those of fish receiving the lower dietary levels of protein. Slightly lower weight gains were obtained when fish were fed diets containing 50 and 60% protein. Although feed conversion values were not statistically different (P < 0.05) among all treatments, the value for the 40% protein diet (1.96) was the best. The mean survival rates were low for all treatments but was highest for the 40% protein diet. No significant difference (P < 0.05) was found in the survival rates of fish receiving different treatments. Results show that a dietary level of 40% protein was required by milkfish fry for maximum growth, efficient feed conversion and high survival rate.

Early effects of nutritional stress on the liver of milkfish, Chanos chanos (Forsskal), and on the hepatopancreas of the tiger prawn, Penaeus monodon (Fabricius).

Abstract After periods of food deprivation and subsequent feeding, hepatocytes of Chanos chanos fry and R-cells of Penaeus monodon juveniles were investigated by means of transmission electron microscope. They clearly reflect the quality of different diets and thus can be used as monitor cells. For purposes of comparison, the same diets were offered to land-dwelling isopods which are known to accept a variety of different diets. Thus, this technique could also be used as a method of determining the effectiveness of binders in artificial diets.

Leucaena leucocephala leaves in formulated feed for Penaeus monodon: a concrete example of the application of histology in nutrition research☆

Abstract Penaeus monodon postlarvae were fed with formulated diets containing either soaked or unsoaked Leucaena leaves. A similarly prepared feed with soybean in place of Leucaena was used for comparison. Results were analysed by statistical and histological methods. Results of the 4-week feeding experiment showed that mean weight gains and percentage survival of the prawns fed with the two Leucaena -containing diets were higher, but not significantly different from soybean-containing diet. The content of the poisonous amino acid mimosine in the Leucaena leaves could be reduced about 70% by soaking the leaves in freshwater for 24 h. Highest weight gain was obtained with the feed containing these soaked leaves. In addition to growth and survival, the R-cells of the midgut glands of the postlarvae were investigated by light and electron microscopy. Although the statistical growth values and the proximate analyses of the test diets were similar, a food-specific ultrastructure was established after only 4 days of feeding. All diets resulted in subcellular characteristics typical for well fed prawns and, at that time, the Leucaena diets were already slightly superior to the soybean control. This indicates that different sources of macronutrients lead to different ultrastructures even if the proximate analyses of protein, carbohydrate and lipid are similar. Only slight changes in the R-cells were observed after 11, 20 and 28 days in the prawns fed with the soybean diet compared to 4 days of feeding. In the diet containing unsoaked Leucaena leaves, however, many R-cells became heavily damaged after 20 and 28 days, whereas the prawns fed with the diet containing soaked leaves exhibited less pronounced distortion. Statistical analyses of growth and survival rate did not show these adverse effects at that time. Although it is highly probable that the mimosine is responsible for those pathological symptoms, complementary experiments could not clearly prove that. The effects of feed components are visible on the cellular or organ level after only a few days, whereas the individuals (organism level) reflect them about 10 days later. Another 10 days later the changes are manifested in the population. Therefore it is suggested to use histology in nutrition studies as a supplementary source of information to statistical and biochemical parameters. The midgut glands can further be used to monitor the nutritional condition of prawns in aquaculture, sea ranching, and in ecological investigations. The study confirms that Leucaena leaves are a promising protein source for prawn diets if mimosine could be reduced to a very low level. A mimosine level of 0.25% in the feed is still too high, if the diet is used uninterruptedly for several weeks.

Milkfish (Chanos chanos)

Milkfish (Chanos chanos Forsskal), the only species known in the family of Chanidae, is an important food fish in the Indo-Pacific regions (Chen, 1976). In some countries, milkfish fingerlings are also used as bait for the tuna fishing industry. This species is best suited for culture in the tropics because of its fast growth, efficient use of natural foods, herbivorous food habit, propensity to consume a variety of supplemental feeds, resistance to disease and handling and tolerance to a wide range of environmental conditions. Milkfish are euryhaline and can thrive in waters of 0 to 150 p.p.t. salinity (Crear, 1980). Milkfish is cultured on a large scale only in the Philippines, Indonesia and Taiwan. Small-scale or experimental production is being practised in a few other Asian countries, such as Thailand, Malaysia, Vietnam and Sri Lanka, and in Hawaii, Guam and Kiribati. Milkfish farming is believed to have begun in Indonesia some 700 years ago (Ronquillo, 1975) and was introduced into the Philippines and Taiwan more than 300 years ago (Ling, 1977). In 1983, milkfish was the single most important species produced through aquaculture in these countries, using more than 500,000 ha of brackish-water and freshwater areas to produce over 365,000 t (Lee and Banno, 1990). In 1990, the cultured area decreased to 410,000 ha but the production increased to about 460,000 t (Lee, 1995; Bagarinao, 1999). In Taiwan, approximately 12,850 ha of ponds were used for milkfish production in 1990 and yielded an average of 7.0 t ha−1. The Phillippines produced 210,900 t of milkfish from 156,177 ha of brackish-water ponds and 19,000 t from about 10,000 ha of freshwater pens, at an average yield of 1.3–1.9 t ha−1. In 1990, Indonesia devoted the largest pond area (231,000 ha) for milkfish production but the average yield was only 0.6 t ha−1.