Nutritional studies on the different life stages of cultured abalone, Haliotis asinina Linne and prawn, Penaeus monodon Fabricius in the Philippines

Abstract

Nutrition and feeding studies were conducted on the various life stages of tropical farmed abalone, Haliotis asinina and cultured shrimp, Penaeus monodon. Studies were focused on diet development and feed evaluation with emphasis on protein/energy levels and protein sources for juvenile abalone. Reproductive performance of abalone broodstock using artificial diet was assessed, Shrimp studies were centered on the quality assessment of feeds and feed ingredients focusing more on the levels of thiobarbituric acid, aflatoxin, urease activity, and calcium:phosphorus ratio and their effects on juvenile and adult shrimp. Utilization of feed pea meal as an ingredient for juvenile shrimp and the response of these animals at this stage to varying protein/energy ratios in the diet were assessed. Testing of diets for the shrimp larvae was likewise done both in small and large scale hatcheries.

1. Abalone Studies. Various diets containing different protein/energy levels were evaluated for abalone juveniles diet development. Biological evaluation included weight gain, increase in shell length, specific growth rate, protein efficiency ratio, feed conversion ratio and for physical evaluation in terms of shell coloration of the animal. Regression analysis showed that growth rate as a function of protein content was optimum at 27% with an energy level of 3150 kcal/kg ME for juvenile abalone, Haliotis asinina. Animals fed the formulated diets produced shells with light bluish green color while those fed seaweed retained the original brown color. Diet formulation containing 27% protein, 5% lipid and 40% carbohydrates with an energy value of 3150 kcal/kg ME was found to be best as basal diet for the rearing of juvenile abalone, Haliotis asinina.. Despite the herbivorous nature of the juvenile Haliotis asinina, a combination of dietary plant and animal protein sources is best in feed preparation for juvenile abalone to attain maximum growth rate. This could be attributed to the fact that some limiting amino acids in plant protein sources such as methionine and lysine may be compensated by the availability of these amino acids in the animal protein sources, thus resulting in a better profile of the diet formulation and better growth for the abalone.

Reproductive performance of broodstock abalone was notably high in those fed the formulated diet alone or in combination with natural diet. Results would suggest that the nutritional quality of the feed has a marked effect on reproductive capability of the animal. Although, it is possible to mature and spawn abalone using natural feed, the provision of an effective artificial diet, given solely or in combination with natural diet may greatly enhance reproductive performance, thus may further result in the production of good quality seeds for abalone hatcheries. Dietary nutrients, especially in terms of proteins, lipids, and fatty acids such as 20:4n-6, 20:5n-3, and 22:6n-3 which are found to be insufficient in natural diet may be compensated with the addition of high quality artificial diet supplement. Fatty acid analysis showed that the n-3/n-6 fatty acid ratios of abalone hepatopancreas reflected those of their diets. The formulated diet had more or less simulated that of mature abalone ovary with an n-3/n-6 ratio of 1.3.

The formulated diet developed not only enhanced growth and reproduction but was also used as a marker for sea ranching and stock enhancement purposes. An experimental release in outdoor tanks with natural growth of seaweeds and diatoms, and in marine reserve showed that the shell band remained clear and distinct, indicating the usefulness of the shell marking method using the artificial diet formulated for abalone juveniles.

II. Shrimp Studies. The performance of an artificial practical diet, kappa-carrageenan microbound diet (C-MBD) was assessed on Penaeus monodon larvae both in small and large scale hatchery operations. Prawns were reared from zoea1 to post-larvae1 using five dietary treatments: (a) natural food, Chaetoceros calcitrans and Artemia salina; (b) C-MBD; (c) combination of natural food and C-MBD; (d) commercial diet (microencapsulated, MED); (e) combination of natural food and commercial diet. Results showed slow development with larvae fed the commercial diet. Feeding with C-MBD in combination with natural food resulted in the highest % survival among treatments (69.6%), but this was not significantly different (P>0.05) from those obtained with larvae fed natural food alone, C-MBD alone or their combination. While mean values for survival of larvae fed the commercial diet, either alone or in combination, was significantly lower (P<0.05) than all treatments, their mean growth indices were comparable with larvae fed C-MBD alone or in combination. The low levels of protein, lipid, and essential fatty acids (which are considered important nutrients during larval development) contained in the commercial diet may well justify the results on metamorphosis, survival and growth of the larvae fed this diet. Same results were noted when larval diets were tested in large scale hatchery operations. Kappa Carrageenan Microbound diet (C-MBD) can be used as partial or total replacement to the traditional algal food.

Field surveys were done and experiments were conducted to assess the quality of shrimp feeds and feed ingredients in the Philippine market. Researches touched mainly on thiobarbituric acid value, aflatoxin level, urease activity, and their biological effects on Penaeus monodon. Experiments on the effects of antioxidants on feed quality and growth of Penaeus monodon juveniles showed that omission of antioxidants from the diet is possible if the feed is to be used within 60 days under ambient conditions. Results may benefit both the feed millers and shrimp growers as it may lower feed production costs. Studies conducted on the response of Penaeus monodon, both pre-adult (ABW=17.5 ± 0.6g) and juvenile (ABW = 5.65 ± 0.13g) stages showed that based on growth performance of the prawns, both stages can tolerate up to 50µg/kg of aflatoxin B1 (AFLB1). Survey results of commercial prawn feed and feed ingredients in the Philippine market showed that 92% contained 40pg/kg and below indicating an acceptable though narrow margin of safety for the end users. Experiments on shrimp quality changes which were monitored through physical evaluation, thiobarbituric acid values (TBA), fatty acid composition and histological examination showed that fat oxidation levels expressed in terms of TBA values of up to 828 mg mal/kg diet did not show detrimental effect on growth of Penaeus monodon. The feed that contained 1262 mg mal/kg diet showed signs of physical deterioration after 6-8 weeks. Urease activity bioassay showed lowest body weight gain with shrimp fed diet containing the unprocessed soybean. This ingredient has been found to contain trypsin inhibitor parallel to this urease activity which if not properly removed or stopped through proper processing may cause concomitant loss of endogenous protein and thus may retard growth of the animal. Adequate heat treatment that need to be applied to soybean meal in order to be an effective shrimp ingredient is 120°C for 20 minutes.

Experiments to control the chronic soft-shell syndrome in Penaeus monodon through dietary manipulation were done. Adult shrimp (17.0-20.0g) collected from brackishwater ponds were induced to become soft-shelled in the laboratory for 3-4 weeks. Eight isocaloric and isonitrogenous diets containing 0:0, 0:1, 1:0, 1:0.2, 1:1, 1:2, 0.2:1, and 2:1 ratios of Ca to P were fed to soft-shelled shrimp.. Shell quality, survival, and growth of shrimp were observed biweekly. The hepatopancreas, exoskeleton, and residual tissues were analyzed to determine the levels of Ca:P.

Shrimp fed diet with 1:1 Ca:P ratio gave the best response in terms of weight gain (62%) and recovery from soft-shelling (89%). Soft-shelled prawns fed Ca:P deficient diet did not improve in shell quality. Survival ranged from 50-100% and was significantly low with shrimp fed the Ca or P deficient diets.

The highest levels of both Ca and P occurred in the exoskeleton of the normal shrimp. The increased levels of these minerals in the hepatopancreas and depressed levels in the exoskeleton in soft-shelled shrimp indicated impaired mobilization of these mineral elements from the former to the latter for use in the formation and hardening of the shell.

The potential of feed pea meal as an alternative protein source to soybean meal for the juvenile Penaeus monodon was assessed. Protein from the feed pea meal replaced 0%, 20%, 40%, 60%, 80%, and 100% of the protein from the defatted soybean meal in the diets. These values were equivalent to 0%, 5%, 10%, 15%, 20%, 25%, respectively of the total protein in the diet. No significant differences (P>0.05) were observed in weight gain, feed intake, feed conversion ratio (FCR) and protein efficiency ratio (PER) of shrimp fed diet 0 up to the highest level of replacement. Survival was high between 75% and 100%. The apparent dry matter (ADMD) and protein (APD) digestibilities of the dry feed pea in Penaeus monodon were high at 73.38 ± 4.98 and 92.74 ± 2.62, respectively. Digestibility coefficients for dry matter and protein for the feed pea meal-based diets increased with increasing level of feed pea replacement. Feed pea meal could be a substitute protein source up to 100% of the protein from defatted soybean meal which is equivalent to 25% of the total protein in the diet. An inclusion level of up to 42% in the juvenile shrimp, Penaeus monodon practical diet did not manifest any adverse effects on growth, feed intake, FCR, survival, body composition, and digestibility coefficients fro dry matter and protein of the shrimp.

The response of Penaeus monodon juveniles to varying protein/energy ratios in test diets was assessed in two sets of factorial experiments. One set of experiment used casein as the sole protein source while the other used a combination of 70%:30% casein:gelatin for its protein source. A two-fold increase in body weight was achieved for shrimp fed diet combinations of 40-50% protein, 5-10% lipid and 20% carbohydrate with energy values of 285-370 kcal/100g regardless of the protein used. Reduction of protein content of the diet from 50% to 40% while maintaining the total energy level at 330 kcal/100g resulted in a non-significant decrease in growth. The inclusion of 15% lipid in the diet produced adverse effects on the animal while sucrose levels beyond 20% resulted in a decreased growth rate. An increase in energy level, at constant dietary protein level resulted in improved utilization of protein and feed conversion efficiency. Shrimp survival was higher with diets containing casein and gelatin as the protein sources than with those containing casein as the sole protein source