THE ASSIMILATION OF PROTEIN AND CARBOHYDRATE FROM PREPARED DIETS BY THE SHRIMP, Penaeus stylirostris

Feed Intake as an Estimation of Attractability in Pacific White Shrimp Litopenaeus vannamei

A simple bioassay that quantifies feed intake as an estimation of relative attractability of feeds containing different ingredients in the Pacific white shrimp Litopenaeus vannamei is described. Fish meal (FM), fish protein hydrolysate (FPH), squid meal (SqM) and casein (CN) were assessed at the same dietary level for their relative influence on feed intake rates of Litopenaeus vannamei. A bland diet containing 92% whole wheat grain meal, 6% diatomaceous earth and 2% alginate with a known low attractability was used as the standard control or base diet. Ingredients were added to the bland base control diet at a level of 3% as fed. Shrimp were stocked into 80 L glass tanks (n= 20 per tank) in a recirculating aquaculture system. Tanks were randomly assigned to one of five diet treatments (3tanks/treatment). Experiments measuring the attractability of each feed were conducted twice daily at 0900 hours and 1330 hours over a five day period. For each experiment, 40 feed pellets (ca. 1 g) corresponding to the assigned treatment were provided to each tank. To calculate the rate of feed intake, pellets remaining in each tank were counted at six minute intervals for a seventy-two minute period. Differences in rate of feed intake among diets were evaluated using Cox Regression Analysis. This attractability assay required only small amounts of ingredients and incorporated ingredients into a bland feed, which significantly reduces the influence from other ingredients or compound in the pellets. All of the test protein ingredients, especially SqM, in the feeds significantly increased the feed consumption rate. The diet containing SqM was consumed at a significantly higher rate than those containing casein and FM but not FPH. FPH and CN containing diets were not significantly different but consumed at a higher rate than the diet containing FM. Results of these trials indicate that the presence of certain ingredients can increase feed intake, thereby increasing nutrient availability of the diets. This reported method to determine consumption of diets containing certain ingredients can be considered as a valid method to estimate attractability.

Nutrition and Functions of Amino Acids in Aquatic Crustaceans

Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptides is essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, H₂S, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.

Relation between reproductive, physiological, and immunological condition of Litopenaeus setiferus pre-adult males fed different dietary protein levels (Crustacea; Penaeidae)

The present study was designed to evaluate the effect of amount of dietary protein levels on blood indicators of protein metabolism and immune condition (blood protein, hemocyanin, osmotic pressure, and hemocytes concentrations), and reproductive capacity of pre-adult Litopenaeus setiferus males (F0). Assessments were made of the relationship between amount of dietary protein, immune condition, and reproductive condition of the shrimp during the maturation process. Three different diets, with different amounts of protein (DP; 35, 45, and 55%), were evaluated over 55 days and compared with shrimp that were from a baseline group before treatments were administrated. Osmotic pressure, hemocyanin, blood protein, and hemocytes were greater in shrimp from control ponds than those obtained of shrimp fed 35 and 45% DP and similar to that obtained in shrimp fed 55% DP, demonstrating that food in the control pond had a nutritional value to that obtained by feeding amounts of dietary protein beyond 45%. Osmotic pressure, hemocyanin (Hc), blood protein (BP), and hemocytes were influenced by amount of DP with the physiology and immune system of shrimp being influenced by diet. At the same time, a maximum reproductive condition (measured as a proportion of normal cells of the total sperm cells) of shrimp males was observed in shrimp fed 45% DPL with lesser normal cells being present in shrimp fed 35 and 55% DPL. These results indicate that an immune reaction can occur in response to dietary protein with excess DP affecting several physiological functions included the sperm synthesis and sperm quality. Influence on hemocytes concentration in shrimp fed protein in excess could activate an attack on sperm cells in the vas deferens provoking lose of sperm quality in such conditions. Results indicate an optimal DP of 45 for maintaining the broodstock bank of L. setiferus.

Influence of dietary carbohydrate on the metabolism of juvenile Litopenaeus stylirostris

The effect of dietary carbohydrates (CBH) on glucose and glycogen, digestive enzymes, ammonia excretion and osmotic pressure and osmotic capacity of Litopenaeus stylirostris juveniles was studied. The increase of CBH, ranging between 1 and 33%, stimulates activities of alpha-amylase and alpha-glucosidase in the hepatopancreas. High levels of glucose in hemolymph and of glycogen in the hepatopancreas were reached at the highest level of dietary CBH; however, the kinetics of accumulation is different. Shrimps fed with low level of CBH needed 3 h to reached glucose peak, whereas only 1 h is necessary for high CBH levels. A saturation curve was observed in glycogen level and alpha-amylase activity with maximum values in shrimp-fed diets containing 21% CBH. This level could be used to be included as a maximum shrimp dietary CBH level. Pre-prandial glycogen levels were observed in shrimp fed a diet containing 1% CBH, indicating an important gluconeogenesis, which affected the protein metabolism. The present results show that a diet containing 10% CBH may not be enough to cover the CBH requirement, which could be satisfied by dietary protein content. The low osmotic capacity observed in shrimp fed on a diet containing 10% CBH coincided with a relatively low post-prandial nitrogen excretion which reflects a low concentration of amino acids circulating in hemolymph, which affected the osmotic pressure and the osmotic capacity. These results reflect the high plasticity of shrimp species to use protein to obtain metabolic energy from food and its limited capacity for processing dietary CBH.