D.M. Smith

Oxygen consumption and ammonia-N excretion in fed and starved tiger prawns, Penaeus esculentus Haswell

Abstract Prawns, 17.7 ± 0.26 g wet weight, were held at 25°C (full moulting cycle at this size, 18–20 days) until 2 days after moulting. Groups of seven, eight or nine were then starved for 5, 10 or 15 days, respectively. Control groups of seven prawns each were fed ad lib for the same periods. The oxygen consumption and ammonia-N excretion over 24 h of each prawn was measured, using antibiotics to minimise bacterial growth during the excretion measurements. Oxygen consumption fell sharply by 24–29% during the first 5 days of starvation and then levelled out. Ammonia-N excretion increased 46–73% with starvation. O:N ratios fell to about 7:1 after the first 5 days of starvation and remained at this level up to 15 days, indicating that protein is virtually the only energy substrate under these conditions. These results support previous research that showed that the carnivorous P. esculentus uses muscle protein preferentially as a source of energy during starvation. In fed prawns, O:N ratios were also low (13.6–16.4:1), indicating that protein is normally a major source of energy.

The effect of feeding frequency on water quality and growth of the black tiger shrimp (Penaeus monodon)

Abstract The feeding strategy used in the commercial culture of shrimp can have a significant impact on pond water quality and hence growth, health and survival of the shrimp, as well as the efficiency of feed utilization. These factors contribute to the profitability of production and to the environmental impact of shrimp farming. The effect of four different feeding frequencies (3, 4, 5 and 6 feedings day −1 ) on the growth and survival of the black tiger shrimp, Penaeus monodon , and water quality was studied in an 8-week growth trial. The shrimp were held in 20×2500-l outdoor tanks containing water and sediment from a shrimp pond. The water management and aeration strategies were designed to simulate a shrimp pond system. The shrimp (initial weight of 5.6 g) were stocked at a density of 25 animals m −2 and fed a widely used, commercial pelleted feed, with all the feed being placed on feeding trays. The uneaten feed on the feeding trays was removed at specific time intervals so that in all treatments, the shrimp had access to the feed for 12 h day −1 . There were no significant ( P >0.05) differences due to feeding frequency on growth rate (1.4±0.08 g week −1 ), feed conversion ratio (FCR) (2.0±0.27) or survival (84±7.6%) of shrimp. Similarly, the water quality parameters (total N, ammonium, nitrate/nitrite, dissolved organic nitrogen, total phosphorus, phosphate, chlorophyll a , oxygen, pH, temperature, salinity, turbidity) were not different among treatments. The results suggest that there is no benefit from feeding P. monodon more frequently than 3 times day −1 when using a feed that is nutritionally adequate and has high water stability. Therefore, it may be possible to reduce feeding frequency in commercial shrimp ponds without adversely affecting water quality, shrimp growth rate and survival, thereby improving farm profitability.

Optimal dietary protein level for juvenile southern rock lobster, Jasus edwardsii, at two lipid levels

This study determined the effect on growth efficiency, nutrient retention and apparent digestibility of varying dietary protein concentration and protein/energy ratio for juvenile southern rock lobster, Jasus edwardsii. Isoenergetic diets were formulated at six crude protein levels (5% increments between 24% and 50%) and at each of two lipid levels (5% and 9%). Duplicate groups of 10 lobsters (initial weight mean 3.58 SE 0.86 g) were held in 50-l tanks, in a recirculating seawater system at 18 degrees Celsius and fed to 95% satiation over a 12-week growth trial. There were significant ( P < 0.05) differences in apparent crude protein digestibility (76.4-83.2%), but no difference in dry matter (mean 59.1 SE 0.8%) or energy digestibility (mean 77.7 SE 0.8%). Survival, feed intake, digestive gland index, protein efficiency ratio, energy efficiency ratio and whole-body composition were not significantly affected by dietary treatment. The relationship between nutrient intake and weight gain indicated optimal dietary digestible crude protein (DCP) levels of 29% and 31% when lobsters were fed diets containing 5% and 9% lipid, respectively. For the two lipid levels studied, the optimal dietary protein/energy requirement was similar for maximum weight gain (29 gDCP/ MJ DE) and feed conversion ratio (FCR, 30 gDCP/MJ DE).

Optimising the essential fatty acids in the diet for weight gain of the prawn, Penaeus monodon

Abstract A study of the influence of the proportion of dietary essential fatty acids (EFA) in the lipid of diets fed to the prawn, Penaeus monodon , showed clearly that these nutrients are required as a proportion of the total fatty acids in the diet. A factorial array of diets were prepared to contain optimal levels (g kg −1 ) of the fatty acids, linoleic (LOA, 18:2 n −6), linolenic (LNA, 18:3 n −3), eicosapentaenoic (EPA, 20:5 n −2) and docosahexaenoic (DHA, 22:6 n −3). As a second factor to the study, the total amount of lipid in the diet was also increased at incremented levels from 45 to 135 g kg −1 at 30 g kg −1 increments. The weight gain of prawns was greatest (156.2±6.2%) when their diet contained 75 g lipid kg −1 , of which 30 g kg −1 was essential fatty acids. Weight gain of prawns fed with diets containing 45 g lipid kg −1 with 17 g of essential fatty acids kg −1 was greater (148.0±3.4%) than prawns fed with the diet that had 45 g lipid kg −1 and 30 g of essential fatty acids kg −1 (124.0±6.8%). The nutritional condition of the prawns, as determined by the amount of lipid in their digestive glands, was generally reflective of weight gain, though there were exceptions, with higher lipid levels in prawn DG from faster growing prawns. The fatty acid composition of the DG lipid generally mimicked that of the dietary lipid. The proportions of each of the essential fatty acids in the DG lipid varied marginally between treatments, but generally LOA, LNA, EPA and DHA levels in the DG fatty acids were present in slightly lower proportions than that in the diet. The amount of dietary lipid present influenced the composition of the fatty acids in the DG lipid when the lowest inclusion level of lipid was compared with the higher inclusion levels. The results of this study clearly indicate that EFA are required as a proportion of the total fatty acids in the diet, and not as a proportion of the diet. Accordingly, it is suggested that EFA should be defined as a percentage of the total fatty acids in conjunction with an indication of the amount of lipid in the diet. This study also showed that for weight gain, the optimal total lipid level of the diet is less than 105 g kg −1 .

Carotenoids in the tiger prawn Penaeus esculentus during ovarian maturation

Female Penaeus esculentus Haswell were collected by 15 to 20 min duration trawls during 1990. Carotenoids were analysed in the digestive gland, abdominal muscle, the remainder of the body (hereafter called “integument”) and ovary of prawns in Stage 2 through Stage 4 (fully mature) of maturation. The only oxycarotenoids (xanthophylls) identified were astaxanthins or astaxanthin esters; occasionally low levels of β-carotene were detected in the digestive gland. The concentrations of astaxanthin monoesters (AM) and diesters (AD) were highest, with only minor amounts of free astaxanthins (Ast), except in the maturing ovaries, where free astaxanthins predominated (up to 80% of the total carotenoid). Of the total carotenoid, 82 to 94% was in the integument, but at maturity the digestive gland contained 10.7±3.4% and the ovary 5.6±0.9% of the total carotenoid. Only the ovary increased in mass during maturation, reaching up to 5.2% of total prawn mass. During this period, digestive gland concentrations of AM, AD and Ast all increased (tota 20 to 120 μg g-1); levels in the muscle and integument varied little throughout maturation (total ∼0.4 and 100 μg g-1, respectively); ovary AM levels remained low throughout (1.5 to 1.2 μg g-1), AD increased from only 2 to 5 μg g-1, but Ast increased from 2 to 34 μg g-1. Apart from the ovary, AM concentrations were the most variable. In common with other decapod Crustacea, the maturing ovary of P. esculentus contained high levels of carotenoids, indicating that these may have an important role in early development. The natural diet of P. esculentus includes a variety of carotenoids, but except for a little β-carotene, the digestive gland, where absorption occurs, contained astaxanthins, with only an occasional trace of β-carotene. This suggests that the conversion of dietary carotenoids to astaxanthin occurs soon after ingestion.

The effects of dietary lipid amount and fatty-acid composition on the digestibility of lipids by the prawn, Penaeus monodon

The digestibilities of the lipid content, and the fatty acids of this lipid, were examined in each of a series of the diets designed to examine the optimal fatty-acid and lipid requirements for the giant tiger prawn, Penaeus monodon. Digestibility of the total lipids was similar for dietary lipid levels of 45, 75 and 105 g kg−1 though the digestibility of total lipids in diets with lipid levels of 135 g kg−1 was significantly (P<0.05) lower. Digestibility of total lipids was unaffected by fatty-acid composition, except when the level of dietary polyunsaturated fatty acids was 17 g kg−1 of the diet and total lipid content was greater than 45 g kg−1. Highest fatty-acid digestibilities were observed for the long-chain highly unsaturated fatty acids, eicosapentaenoic (20:5n−3) and docosahexaenoic (22:6n−3) acids. High levels of digestibility were observed for all fatty acids with unsaturated bonds including the monounsaturated fatty acid, oleic acid (18:1n−9). Longer-chain saturated fatty acids were the least digestible, with digestibilities diminishing as fatty-acid chain length increased. The results of this study clearly demonstrate that amount of lipid in the diet influences its own digestibility and also that the fatty-acid composition of the total lipid in the diet influences the digestibility of the total lipid and also that of the individual fatty acids.

Biochemical composition of some prey species of Penaeus esculentus Haswell (Penaeidae: Decapoda)

A representative collection was made of the very small prey animals that comprise the diet of juvenile Penaeus esculentus in seagrass beds in Moreton Bay, Australia (three gastropod species; two bivalves; four crustaceans; one polychaete). Proximate analyses were made of each group, and whole animals were analysed for total amino acids, lipid classes and fatty acids. The mean protein content ranged from 67 to 83% of ash-free dry weight, the lipid from 10 to 21% and the carbohydrate from 6 to 22%. The amino acid composition was fairly uniform in all species and, except for isoleucine which was lower, similar to that of P. esculentus muscle. Sterols and sterol esters were mostly above 3% of ash-free dry weight; phospholipids ranged from 22 to 80% of total lipid, with phosphatidylcholine a major component in most cases. Saturated fatty acids were <45% of total fatty acids, except in one bivalve; polyunsaturated fatty acids (PUFA) ranged from 23 to 56% of the total, but levels of C18 PUFA were mostly <3% of the total; C20: 4ω6 and higher PUFA were abundant. Overall, the natural diet of P. esculentus is high in protein, with relatively low mean carbohydrate (10.6%) and lipid (12.3%), and with a high proportion of PUFA in the lipid fraction. The relevance of this to empirically derived aquaculture diets is discussed.

Effect of dietary cellulose on digestion in the prawn Macrobrachium rosenbergii

The effects of dietary cellulose on digestion and absorption in Macrobrachium rosenbergii were studied by inclusion of α-cellulose at the expense of starch into four purified diets. The results showed that increasing α-cellulose reduced the apparent digestibility of both dry matter and protein, but also showed that cellulose itself is digestible, with an apparent digestibility of 80%. Increasing dietary levels of cellulose caused an increase in cellulase levels in the gastric fluid, and a decrease in amylase levels in gastric fluid and hepatopancreas. The activity of cellulase was highest between 60 and 180 min after feeding. Increased levels of dietary cellulose were associated with lowered levels of protein in the gastric fluid, and increased levels of protein in the hepatopancreas. Total reducing sugars in the hepatopancreas and glucose in the hemolymph also increased with higher levels of dietary cellulose. Increasing dietary cellulose caused no increase in volatile fatty acids (VFA) in either the gastric fluid or the hemolymph, or in total lipids in the hepatopancreas. It was concluded that the digestion of cellulose in M. rosenbergii was not due to fermentation by endosymbionts producing volatile fatty acids, but to the presence of cellulase which released glucose that was apparently absorbed into the hemolymph, and therefore, dietary cellulose can be a source of both digestible and metabolizable energy for this organism.

The use of enriched 15N as an indicator of the assimilation of individual protein sources from compound diets for juvenile Penaeus monodon

Abstract We examined the potential of using an enriched stable isotope ( 15 N) to trace the assimilation of individual protein sources from compound aquaculture diets by juvenile Penaeus monodon . We used the marine diatom Chaetoceros muelleri as a source of plant protein and the brine shrimp ( Artemia ) as a source of animal protein. The diatoms were labelled by replacing 5% of the nitrogen in their culture nutrient media with 15 N enriched KNO 3 . The Artemia were labelled by feeding them 15 N enriched diatoms. The 15 N enriched diatoms and Artemia were each incorporated into a standard compound pelleted diet. The pellets were fed to juvenile P. monodon (weight range 2 to 5 g) in the laboratory and in enclosures at a local prawn farm. Analysis of the percentage 15 N in the abdominal muscle of juvenile prawns demonstrated rapid assimilation of the enriched isotope from diatoms and Artemia . There was a progressive increase in the percentage 15 N in the abdominal muscle during the 4-week experiment. Application of a simple mixing model showed that the relative assimilation rate of enriched nitrogen from Artemia was approximately 4.3 times that of the diatoms after 2 weeks and approximately 3.6 times that of diatoms after 4 weeks. The results demonstrated that enriched stable isotope tracers can provide rapid and direct information about the assimilation and retention of nitrogen from individual protein sources in compound diets for shrimp.

Comparison of triacylglycerols, esterified and free fatty acids as neutral lipid sources in the diet of the prawn Penaeus monodon

Penaeus monodon were fed purified diets in which the sole neutral lipid source had a defined fatty acid composition supplied as either triacylglycerols (TAG), free fatty acids (FFA), ethyl esters (EE) or methyl esters (ME). Nutrient intake across treatments was kept constant through sub-satiation feeding. After 50 days, the percent weight gain of prawns fed the TAG diet (94 ± 6%) was markedly higher than those fed the FFA diet (84 ± 7%) and significantly higher (P < 0.05) than those fed the ME (73 ± 7%) or EE (54 ± 5%) diets. Poor growth of prawns fed the EE and ME diets was attributed to the inability of prawns to either digest and/or metabolise the ethyl and methyl esters effectively. The apparent digestibility of neutral lipid in the EE diet was significantly lower (90.9 ± 0.9%) than in the other diets (96.5 ± 0.9%: TAG, 98.1 ± 0.6%: FFA, 96.1 ± 0.9%: ME). The digestive gland (DG) of prawns fed the TAG diet had the greatest amount of total lipid. DG lipids of prawns fed the TAG and FFA diets contained similar proportions of neutral and polar lipids (≃ 55% neutral, 45% polar), whereas with the EE diet, neutral lipids dominated (70%) and with the ME diet there was a higher proportion of polar lipid (68%). DG neutral lipids of both the TAG and FFA-fed prawns had high proportions of triacylglycerols and diacylglycerols with small quantities of both cholesterol and free fatty acids. However, prawns fed the ME and EE diets differed from the TAG-fed prawns in both the proportions and total quantities of DG neutral lipids. The DG polar lipids in prawns from the TAG, FFA and EE treatments had similar proportions of each polar lipid class, in contrast to those fed ME where the polar lipid was almost exclusively phosphotidylethanolamine. The fatty acid composition of the total DG lipid of prawns fed the TAG and FFA diets were similar. There was virtually no PUFA and HUFA in the DG lipid of the ME-fed prawns. These studies demonstrate that where a diet with a particular fatty profile is required, trigacylglycerols either singly or as a mixture should be used. If these do not give the required fatty acid profile, free fatty acids may be used to adjust the profile. The use of either methyl or ethyl esters as neutral lipid components in experimental diets is not recommended for examination of fatty acid requirements of P. monodon.