Ilda G. Borlongan

Studies on the digestive lipases of milkfish, Chanos chanos.

Milkfish grown on two natural foods were examined to determine the distribution pattern of the digestive lipases along the digestive tract and to identify the optimum condition for lipase activity. One food consisted of a biological complex of unicellular algae and diatoms (Food A) and the other consisted of fibrous filamentous green algae, predominantly Chaetomorpha brachygona (Food B). The major sites of lipase secretion in milkfish digestive tract were the intestines, pancreas and pyloric caeca. Lipase activity was somewhat higher for fish grown on Food A than those grown on Food B. Intestinal lipase activity was observed to be maximal at 45°C and at pH 6.8 and 8.0. Activity of pancreatic lipase was observed to be maximal at 50°C and at pH 6.4 and 8.6. The detection of two well-defined pH optima, one at slightly acidic and the other at alkaline pH for both the intestinal and pancreatic lipases suggests a physiological versatility for lipid digestion in milkfish.

Lipid and fatty acid composition of milkfish (Chanos chanos forsskal) grown in freshwater and seawater

Abstract The lipid and fatty acid compositions of the various organs of milkfish fed with an invariant diet and reared in seawater (SW) and freshwater (FW) were determined using column chromatography and gas chromatography. Phospholipid content of the gills, kidney, liver, intestines and depot fat was higher in SW than in FW while the organs from fish in FW had higher contents of neutral lipid. Fatty acid patterns of total lipids in the liver, intestines and depot fat of milkfish reared in FW and SW were similar. There were marked differences in fatty acid patterns of gills and kidney. The proportions of saturated to unsaturated fatty acids in gills and kidney were lower in SW than in FW. Likewise, the ratio of n -3 to n -6 fatty acids and total polyunsaturated fatty acids (PUFAs) of gills and kidney were higher in SW than in FW. The fatty acid patterns of the phospholipid fractions showed that SW-reared milkfish have higher total PUFAs, especially of the n -3 fatty acids, than the FW-reared milkfish not only in gills and kidney but in all organs examined. The differences in lipid and fatty acid composition reflect a physiological response to the salinity in which milkfish were reared.

Quantitative Lysine Requirement of Milkfish (Chanos chanos) Juveniles

Abstract A feeding experiment was conducted to determine the quantitative dietary requirement of milkfish juveniles for lysine. Milkfish (Chanos chanos Forsskal) of mean weight 5.92±0.14 g were fed diets containing 7.0, 11.0, 15.0, 19.0, 23.0 and 27.0 g lysine/kg dry diet for 12 weeks. The amino acid test diets contained white fish meal and zein supplemented with crystalline amino acids to provide an amino acid profile similar to milkfish proteins except for lysine. Each of the six diets was fed to four replicate groups of 25 fish in a completely randomized design and at a feeding rate of 5% of the fish body weight per day. On the basis of the growth response, lysine requirement of juvenile milkfish was found to be 20 g/kg diet. This value corresponds to 4.0% when expressed as a percentage of the dietary protein. Survival (94–97%) was consistently high in all treatments. Except for loss of appetite resulting in low food intake and depressed growth, no nutritional deficiency signs were observed in fish given the lysine-deficient diets.

Techniques on algae harvesting and preservation for use in culture and as larval food

A method of algae harvesting and preservation was developed. Test algal species consisted of two diatoms: Chaetoceros calcitrans and Skeletonema costatum, and two flagellates: Tetraselmis chui and Isochrysis galbana. Chemical flocculation using alum and lime were evaluated as methods of harvesting algae. Freezing and sun-drying were used as methods of preservation with viability tests done on frozen samples. The usefulness of sun-dried algae was evaluated through its ability to support survival of Penaeus menodon larvae. Results showed that alum and lime flocculation were effective for Chaetoceros, Tetraselmis and Skeletonema but ineffective for Isochrysis. Optimum pH for algae removal with alum was found to be 6.5. With lime, algae removals increased with pH and was optimum at pH 9.5. A simple freezing technique preserves the viability of algal concentrates for culture purposes. Good performance of sun-dried Chaetoceros and Tetraselnlis suggests that these algae may be used as larval feed for Penaens monodon alone or supplementarily to eliminate complete dependence on carefully-timed live algal production.

Arginine and threonine requirements of milkfish (Chanos chanos Forsskal) juveniles

Abstract Growth studies were conducted with milkfish ( Chanos chanos Forsskal) juveniles to determine the quantitative requirements for arginine and threonine. The amino-acid test diets (40% crude protein) contained casein and gelatin supplemented with crystalline L-amino acids to provide an amino-acid profile similar to milkfish protein except for the test amino acid. Each set of experimental diets consisted of six isonitrogenous and isocaloric diets containing graded levels of the essential amino acid to be tested. Break-points in the growth curves which represent the optimum dietary concentration of arginine and threonine for fish growth were determined by the broken-line regression method. Based on dry diet, the requirement of milkfish juveniles for arginine is 2.10% and for threonine, 1.80%. These values correspond to 5.25% arginine and 4.50% threonine when expressed as a percentage of dietary protein.

Potential of feed pea (Pisum sativum) meal as a protein source in practical diets for milkfish (Chanos chanos Forsskal)

Abstract A 12-week feeding trial was conducted to evaluate the use of feed pea meal as a dietary protein source for juvenile milkfish. Six isonitrogenous (30% crude protein) and isocaloric (16.5 kJ/g) practical diets were formulated. The control diet contained fish meal, soybean meal, meat and bone meal and copra meal as principal protein sources. Feed pea meal was progressively substituted at 0%, 5%, 10%, 15%, 20%, 25% and 30% of total protein. A leading commercial milkfish feed was also tested as an additional control. The experimental diets were fed to triplicate groups of milkfish fingerlings (mean initial weight of 0.42±0.01 g) at 10% body weight/day. Growth performance (expressed as percentage of weight gain and SGR), survival, feed conversion ratio (FCR) and protein efficiency ratio (PER) of milkfish fed diets with up to 10% substitution of the dietary protein with feed pea meal were not significantly different ( P >0.05) compared to fish fed the control diet. Replacement with feed pea meal at 15% and higher levels led to milkfish fed these diets showing a significantly lower growth response compared to fish fed with the control without any feed pea meal. Nevertheless, it was observed that milkfish fed diets with up to 20% of total dietary protein substitution with feed pea meal showed better growth rates and feed conversion ratios than the commercial feed control. Whole body composition (crude protein, crude fat, crude fiber, nitrogen-free extracts and ash content) of milkfish fed the various test diets was not significantly different. Apparent digestibility coefficients of feed pea meal and experimental diets in milkfish were also determined. Results indicate that feed pea meal is an acceptable protein source and can replace up to 20% of the total dietary protein in milkfish diets.

The essential fatty acid requirement of milkfish (Chanos chanos Forsskal)

The essential fatty acid (EFA) requirement of milkfish was examined by a 12-week feeding trial using defined, purified diets at water temperature of 28–29°C and salinity of 32‰. The test diets contained varying levels of 18:0 (triglyceride form, TG), 18:3(n−3), 18:2(n−6) and (n−3) highly unsaturated fatty acids (n−3 HUFA). Milkfish juveniles were starved for 7 days and were than fed lipid-free diet for 30 days before the initiation of feeding trials. Low growth and feed efficiency together with high mortalities were observed in fish fed the lipid-free diet as well as in the EFA-deficient diet. Supplementation of 2% 18:2(n−6) to the tristearin based diet did not improve growth rate of milkfish as effectively as feeding with (n−3) fatty acids. The highest weight gain was obtained in milkfish fed a combination of 5% 18:0 + 1.0% 18:3(n−3) + 0.5% 20:5(n−3) + 0.5% 22:6(n−3) although the supplementation of 2% 18:3(n−3) alone or combination of 0.5% 20:5(n−3) + 0.5% 22:6(n−3) to the tristearin based diets were also effective for improvement of growth. Thus, (n−3) fatty acids, such as 18:3(n−3) and (n−3)HUFA were nutritionally more important than 18:2(n−6) for milkfish. The fatty acid composition of the polar lipids from whole body of milkfish juveniles fed the various test diets were influenced by the composition of the dietary fatty acids.

Measures of egg quality in induced spawns of the Asian sea bass, Lates calcarifer Bloch

The egg morphometry and lipid and protein components were determined in induced spawns (n=14) of the sea bass, Lates calcarifer, to identify measures of egg quality. Based on fertilization and hatching rates, the spawns were classified either in Group I, (zero fertilization) or Group II (where fertilization and hatching occurred). The egg morphometry did not differ between the two groups (p > 0.05). The total lipid was higher in Group II than in Group I, although the difference was not significant (p > 0.05). The EPA and linoleic acid were significantly higher in Group II (p < 0.05). There were positive correlations between the total saturated fatty acids and fertilization rate (p < 0.05; r=0.58), the total saturated fatty acids and percentage of normal zygotes (p < 0.02; r=0.62), and DHA and the percentage of normal zygotes (p < 0.04; r=0.56). The total protein and FAAs were higher in Group I than in Group II, but the differences were not significant (p > 0.05). Proline, glycine, p-ethanolamine, and aspartic acid were significantly higher in Group II (p < 0.05), while tyrosine and glutamic acid were significantly higher in Group I (p < 0.05). Phosphoserine and fertilization rate were positively correlated (p < 0.03; r=0.60), as well as aspartic acid and hatching rate (p < 0.05; r=0.54). Arginine was negatively correlated with fertilization rate (p < 0.03; r=−0.61) and the percentage of normal zygotes (p < 0.03; r=−0.63). Serine was inversely correlated with yolk volume of the newly-hatched larvae (p < 0.03; r=−0.77). The moisture content of the eggs, which was significantly higher in Group II than in Group I (p < 0.03), was directly correlated with the FAAs:protein ratio (p < 0.03; r=0.76). The present results reveal egg components that may be used as quality measures in induced spawns of sea bass, a euryhaline teleost that spawn pelagic eggs containing an oil globule.

Growth and production of milkfish (Chanos chanos) in brackishwater ponds: effects of dietary protein and feeding levels

Abstract The most economical combination of dietary protein and feeding levels for milkfish culture in brackishwater ponds was determined. Milkfish juveniles (average weight, 5 g) were stocked at 7000/ ha and fed two diets containing 24% or 31% dietary protein at 2 or 4% of body weight. There was no interaction between feeding level and dietary protein on growth, feed efficiency, and energy assimilation of milkfish. This indicates that the response of milkfish to change in protein levels is not influenced by ration size. Regardless of protein levels, the final weight, weight gain, specific growth rate, and production of milkfish were significantly higher (α = 0.05) when fed at 4% body weight than at 2%. As culture progresses, differences in weights of fish fed varying protein levels were still insignificant. This could be attributed to the balanced amino acid profile of both diets. The higher growth at the 4% feeding level could be due to the higher amount of amino acids available for protein synthesis. Higher energy assimilated by milkfish at higher feeding rate demonstrates that energy supply also influences growth. Partial budgeting analysis shows that bigger profits can be earned by using a 24% protein diet with balanced amino acids at a feeding rate of 4% of body weight. The greater amount of feed given at higher rate can be compensated by faster growth and higher production.

Dietary requirement of milkfish (Chanos chanos Forsskal) juveniles for total aromatic amino acids

Abstract The phenylalanine requirement of milkfish at two dietary tyrosine levels was determined using a 2× 6 factorial feeding experiment. The amino acid test diets (45% crude protein) contained vitamin-free casein and gelatin supplemented with crystalline L-amino acids to provide an amino acid profile similar to milkfish tissue protein except for the test amino acid. The experimental diets consisted of 12 isonitrogenous and isocaloric diets containing six graded levels of phenylalanine (1.18, 1.3, 1.6, 1.9, 2.2, and 2.5% of dry diet) at two levels of tyrosine (0.45 and 1.2% of dry diet). Each of the 12 diets was fed to triplicate groups of 15 milkfish juveniles (initial mean weight = 0.58 ± 003 g) for 12 weeks. Breakpoint linear regression analysis of the growth data estimated the phenylalanine requirement to be 1.90% of the dry diet (4.22% of dietary protein) at 0.45% dietary tyrosine. In the presence of 1.2% dietary tyrosine, the phenylalanine requirement was estimated to be 1.26% of the dry diet (2.80% of dietary protein), suggesting that tyrosine can supply a portion of the total aromatic amino acid requirement thereby sparing phenylalanine. The optimum total aromatic amino acid requirement of milkfish obtained in the study was 5.22% of dietary protein and the replacement value of tyrosine for phenylalanine was computed to be about 46%. Total aromatic amino acid levels higher than 6.88% caused a significant depression of growth in milkfish juveniles.