Optimization of Lipid Extraction and Determination of Fatty Acid Compositions in Edible Meats of Freshwater and Marine Shrimps

Response surface methodology was applied to determine optimal conditions for lipid extraction from shrimp. Box-Behnken Design including independent variables such as extraction time, extraction temperature, and ratio of mixed solvents was used. The optimal conditions for lipids extraction were the use of petroleum ether:ethyl acetate (2.3:1, v/v) with 62 min of extraction at 52ºC. Under the optimal conditions, the extraction yields of lipids from Euphausia superba, Penaeuschinesis, Macrobranchium nipponense, and M. rosenbergii were 4.39, 2.80, 2.98, and 3.30%, respectively. Gas chromatographic analysis showed that M. rosenbergii presented the highest level of polyunsaturated fatty acid (PUFA) (48.28%) among the shrimps studied. In addition, the 20:5n3 (EPA) + 22:6n3 (DHA) value (26.43%) was second only to E. superba (31.27%). The finding suggests that M. rosenbergii is a potential PUFA source for food supplementation.     

Variation in the Fatty Acid Composition Between and Within Two Mantis Shrimp Species,Harpiosquilla harpax and Miyakea nepa: Impact of Season and Sex

ABSTRACT

Harpiosquilla harpax and Miyakea nepa are two out of 400 marine crustaceans commonly known as mantis shrimp. Mantis shrimp are commercially valuable and can be found in fish markets of some Mediterranean and many Asian countries. This study focused on a comparative analysis of variation throughout the year in regards to proximate and total fatty acid composition in the muscle of male and female H. harpax and M. nepa. The most abundant fatty acids identified in the muscle of both species were C16:0, C18:0, docosahexaenoic acid (DHA; C22:6n-3), eicosapentaenoic acid (EPA; C20:5n-3), and C20:4n-6. Results of this study revealed that the muscle fatty acid profiles of H. harpax and M. nepa were not significantly different (p > 0.05), except for C14:0, C16:0, C22:0, and DHA amounts, and were mostly influenced by sex within each sampling month. Generally, the muscle of H. harpax contained higher (p < 0.05) levels of DHA than the muscle of M. nepa. The male mantis shrimp, within each species and most of the sampling months, appeared to have higher (p < 0.05) DHA, total n-3 polyunsaturated fatty acid (PUFA), and PUFA/saturated fatty acid ratio compared to the females. Both species could be considered as a good source of n-3 PUFA in the human diet.     

Long‐chain PUFA enrichment in microalgae and metabolic dynamics in Tapes philippinarum larvae

The possibility of increasing n‐3 and n‐6 long‐chain polyunsaturated fatty acids (PUFA) content in microalgal mixtures used to feed Tapes philippinarum larvae was explored by lowering culture temperature from 26 to 14 °C. Although fatty acid composition of different microalgal species has a genetic basis, the algal cultures grown at 14 °C significantly increased the content of long‐chain n‐3 PUFA in Isocrysis galbana and in Thalassiosira pseudonana, while in Tetraselmis tetrathelo, the PUFA increase only involved shorter chain PUFA, namely 16:4n‐3 and 18:4n‐3. However, larvae fed on the PUFA enriched microalgal mixture did not show improvements in growth and survival performances with respect to the control group fed the microalgal mixture grown at 26 °C. From a biochemical perspective, two key aspects emerged from the results: (i) clam larvae have adequate biotransformation and selection skills to adjust fatty acid profile to their requirements as they can even modulate the incorporation of essential long‐chain PUFA as 20:5n‐3 and 22:6n‐3 when the dietary supply exceeds the physiological requirements; (ii) bivalve can biosynthesize non‐methylene‐interrupted dienoic (NMID) fatty acids as confirmed by the constancy of relative proportion with larvae growth in spite of the NMID fatty acid absence in the diet.     

Evaluation of Schizochytrium meal in microdiets of Pacific white shrimp (Litopenaeus vannamei) larvae

A feeding trial was conducted to assess the effects of dietary Schizochytrium meal supplementation on survival, growth performance, activities of digestive enzymes and fatty acid composition in Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Four isonitrogenous and isolipidic diets were formulated to contain graded levels of Schizochytrium meal: 0% (S0, the control diet), 2% (S2), 4% (S4) and 6% dry matter (S6). Results showed that there was no significant difference in survival of shrimps among dietary treatments (P > 0.05). Shrimps fed diets with 2% and 4% microalgae meal had significantly higher specific growth rate (SGR) than that of shrimps fed diets with 0% and 6% microalgae meal, and no significant differences were observed between shrimps fed diets with 2% and 4% microalgae meal (P > 0.05). Activity of trypsin in the pancreatic and intestinal segments, and activity of amylase in the pancreatic segments were not significantly affected by dietary microalgae meal levels (P > 0.05). Specific activities of both alkaline phosphatase and leucine‐aminopeptidase in intestine and purified brush border membrane of intestine were significantly higher in shrimps fed diet with 2% microalgae meal (P < 0.05). There were no significant differences in C18:2n‐6, n‐3 fatty acids, n‐6fatty acids, PUFA and n‐3/n‐6 in muscle samples among dietary treatments. C16:1n‐7, C18:1n‐9, MUFA, C18:3n‐3 and C20:5n‐3 decreased, however, C20:4n‐6 increased in the muscle as dietary microalgae meal level increased. In conclusion, 4% Schizochytrium meal in microdiets of shrimps can improve growth performance and may be a valuable additive in the microdiets of shrimps.     

Nutritional values of Apocyclops dengizicus (Copepoda: Cyclopoida) fed Chaetocerous calcitrans and Tetraselmis tetrathele

The cyclopoid copepod Apocyclops dengizicus was isolated from a marine shrimp pond, Penaeus monodon, Kuala Selangor, Malaysia, and reared in the laboratory for 3 months to establish a pure population stock. Amino acids and fatty acids of A. dengizicus were determined when fed Chaetocerous calcitrans (C), Tetraselmis tetrathele (T) and their combination (CT) (1:1 by number). The protein contents in A. dengizicus that received C, T and CT were 46.8%, 60.5% and 55.3% of dry weight respectively. Correspondingly, the lipid was 19.0%, 17.8% and 19.1% of dry weight for C, T and CT respectively. The A. dengizicus cultured on C, T and CT had total essential amino acids without tryptophan measurement of 57.1, 60.3 and 67.8 and total non‐essential amino acids of 42.9%, 40.0% and 32.2% of total amino acids. The fatty acid content of A. dengizicus showed that it was able to synthesize docosahexenoic acid (22:6n‐3, DHA), eicosapentaenoic acid (20:5n‐3, EPA) and arachidonic acid (20: 4n‐6, ARA) from examined microalgal diets. The DHA:EPA:ARA ratios of A. dengizicus fed on C, T and CT were 6.8:3.0:1, 14.0:5.8:1 and 11.6:2.6:1 respectively. Apocyclops dengizicus could be suitable live food for larval fish and shrimp rearing because it meets their nutritive requirements.     

A description of the ovarian development stages of penaeid shrimps from the coast of Pakistan

In this study, four species of penaeid shrimp from Pakistan's inshore waters were studied. These were Penaeus penicillatus (Alcock), Penaeus merguiensis (de Man), Metapenaeus affinis (Milne Edwards) and Parapenaeopsis stylifera (Milne Edwards). During maturation, shrimp ovaries pass through a series of colour changes. The various colours observed in the ovaries of the four species of penaeid shrimps were translucent, white, cream, yellow, green‐yellow, green‐white, light green and dark green. The different type of oocytes observed in histological sections of the penaeid ovaries are as follows: chromatin nucleolar oocytes, perinucleolar oocytes, yolkless oocytes, yolky oocytes and oocytes with cortical bodies. The ovarian developmental stages recognized in these shrimps are: undeveloped, developing, nearly ripe, fully ripe, resorbing and resorbing/ developing. The ovarian developmental stages were similar in all the four species with the exception of the fully ripe stage. In the fully ripe stage of P. penicillatus and P. merguiensis, the cortical bodies were present at the periphery in two shapes; spherical as well as rod‐like. On the other hand, in the fully ripe stage of M. affinis and P. stylifera, the cortical bodies were present only at the periphery and were only spherical. A relationship between colour of ovaries and histological stages of ovarian development was established. A female shrimp with a dark‐green ovary is an indication of the ready‐ to‐spawn condition. In P. merguiensis and Penaeus penicillatus, respectively, 100% and 88.1% females with dark‐green ovaries had oocytes with cortical bodies, whereas in M. affinis and P. stylifera, respectively, 50% and 28.6% females with dark‐green ovaries had oocytes with cortical bodies.     

Nutritional evaluation of fatty acids for the open thelycum shrimp, Litopenaeus vannamei: II. Effect of dietary n-3 and n-6 polyunsaturated and highly unsaturated fatty acids on juvenile shrimp growth, survival, and fatty acid composition

This study evaluated the nutritional value of dietary n‐3 and n‐6 polyunsaturated fatty acids (PUFA) such as linoleic (LOA) and linolenic (LNA) acids, and highly unsaturated fatty acids (HUFA) such as arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids for juvenile Litopenaeus vannamei, based on their effects on growth, survival, and fatty acid composition of hepatopancreas and muscle tissue. Diets contained 5% total lipid. A basal diet contained palmitic and stearic acids each at 2.5% of diet. Five diets contained 0.5% dry weight of LOA, LNA, AA, EPA, or DHA. An additional diet evaluated HUFA in combination by supplementing at 0.5% of diet, a mixture of n‐3 HUFA. All HUFA showed higher nutritional value than PUFA for shrimp and produced significantly (P < 0.05) higher final weight, weight gain, and total lipid in shrimp muscle. Fatty acid profiles of shrimp tissues reflected the composition of the dietary lipids. In general, saturated fatty acids were more abundant in the neutral factions, while PUFA and HUFA were more abundant in the polar fractions of tissues. Under these experimental conditions, HUFA had much greater nutritional value than PUFA for juvenile L. vannamei; moreover, dietary requirements for PUFA were not demonstrated.     

Enhancement of survival and metamorphosis rates of <Emphasis Type="Italic">Penaeus monodon</Emphasis> larvae by feeding with the diatom <Emphasis Type="Italic">Thalassiosira weissflogii</Emphasis>

The purpose of this study was to compare the performance of two species of diatoms, Thalassiosira weissflogii and Chaetoceros gracilis, in the larviculture of the black tiger shrimp Penaeus monodon. Shrimp larvae were fed with either C. gracilis, T. weissflogii, or a combination of the two species of diatoms. The larvae fed solely with T. weissflogii or a combination of the two types of diatom had significantly higher survival rates and faster metamorphosis than those fed solely with C. gracilis. The numbers of diatom cells consumed by larvae during 3-h periods were determined, revealing that larvae consumed significantly higher numbers of C. gracilis than T. weissflogii. However, when the protein, total fatty acid, and polyunsaturated fatty acid content of the two species of diatom are compared, significantly higher amounts of each are found in T. weissflogii. Converting the number of diatom cells consumed into equivalent protein, total fatty acid, eicosopentaenoic acid, and decosahexaenoic acid reveals that larvae fed with T. weissflogii received significantly higher amounts of all the nutrients, compared to those consuming C. gracilis. The results showed an advantage of feeding T. weissflogii to C. gracilis in enhancing survival and metamorphosis in P. monodon larvae.     

Use of a <Emphasis Type="Italic">Noctiluca</Emphasis>-killing bacterium <Emphasis Type="Italic">Marinobacter salsuginis</Emphasis> strain BS2 to reduce shrimp mortality caused by <Emphasis Type="Italic">Noctiluca scintillans</Emphasis>

The ability of an algicidal bacterium Marinobacter salsuginis strain BS2, isolated from shrimp pond water, to reduce shrimp mortality was investigated under laboratory conditions. When two species of shrimp (Penaeus monodon and Litopenaeus vannamei) (body length 1.5–1.8 cm) were cultured together with the dinoflagellate Noctiluca scintillans, nearly 80 % of the shrimps died within 7 days. However, when bacterial strain BS2 was also added to the culture, N. scintillans was killed within 48 h, and shrimp survival rates on the 7th day improved from 23 to 87 % for both P. monodon and L. vannamei. The bacterium BS2 alone had no effect on shrimp condition. Under conditions of increased dissolved oxygen, the effect of using BS2 was greater, and shrimp survival rates improved even more dramatically, from 26 to 98 %. These studies provide the first evidence that the use of killing bacteria, isolated from shrimp culture water, can suppress harmful algal blooms (HABs) and thus restore the efficiency of shrimp production. The control of HABs in this way in shrimp culture farms would be a major benefit for shrimp production.     

Effects of Decomposing Rhizophora apiculata Leaves on Larvae of the Shrimp Penaeus monodon

We studied the effects of different concentrations of decomposing Rhizophora apiculata leaves and their leachates on larvae of the shrimp Penaeus monodon under laboratory conditions. Shrimp mortality was highly dependent on the concentration of oxygen in the water, which in turn was strongly correlated to the amount of decomposing leaves in the same water. Shrimps died after 5 min when placed in water containing the highest concentration of mangrove leachates (15 g l⁻¹) tested in our experiments. Shrimp survival and biomass decreased significantly when the shrimp were cultured at the relatively higher concentrations of leaves and leachates (10 and 15 g l⁻¹); in contrast, moderate amounts of leaves or their leachates (2.5–5 g l⁻¹) had positive effects on shrimps. The survival and biomass of shrimps cultured with plastic leaves was lower than those of shrimps cultured with mangrove leaves, indicating that food derived from mangrove leaves contributed to a higher shrimp survival and biomass. These results have important implications for the culture of shrimps in extensive mangrove-shrimp systems. While litter may promote shrimp production, high leaf concentrations may have negative effects due to the drop in the oxygen concentration. Water circulation may help to prevent low oxygen conditions and reduce local accumulations of mangrove leaves.     

Seasonal and nutritional effects on the fatty acids of three species of shrimp, Penaeus setiferus,P. aztecus and P. duorarum

The fatty acids of three species of shrimp from the Gulf of Mexico, white (Penaeus setiferus), brown (P. aztecus), and pink (P. duorarum), were analyzed periodically for 1 year. The fatty acid patterns of varied species of shrimp collected at the same time of the year differed very little from each other. On the other hand, a slight but distinctive seasonal variation of the fatty acid composition, irrespective of Penaeus species, was observed. Saturated fatty acids increased during the warm seasons and decreased during the cold months, while the opposite behavior was exhibited by monoenoic and polyenoic fatty acids. When the variations in fatty acid levels were compared to the temperature of the water, there was a 2-month lag period between a change in water temperature and the corresponding variation in fatty acid composition. This slow alteration of the shrimp fatty acids suggests that the changes are effected through the food chain rather than by endogenous adjustment to an alteration in water temperature.Further studies were performed in which the fatty acid patterns of pond- and laboratory-reared shrimp were compared with those of their food. Evidence was obtained confirming the significant effect of diet on the fatty acids of shrimp lipids. Shrimp incorporated certain dietary fatty acids readily but showed little ability for the conversion of C₁₈ polyunsaturated fatty acids into C₂₀ and C₂₂ fatty acids of higher unsaturation. Thus, the C₂₀ and C₂₂ fatty acids which are essential for shrimp growth cannot be substituted in the diet by C₁₈ precursors.Considered in toto, these experiments suggest that diet exerts a strong influence on the composition of shrimp body lipids and that, contrarily, endogenous synthesis or modification occurs to a low degree.     

The Effects of Natural Antioxidant Extract Isolated from Giant Red Shrimp (Aristaeomorpha foliacea) Shells on Fatty Acid Profiles of Anchovy (Engraulis encrasicolus) During Refrigerated Storage

The aim of the present study was to determine the effects of natural antioxidant extract isolated from the shells of giant red shrimp (Aristaeomorpha foliacea) on the changes in fatty acid profile of anchovy (Engraulis encrasicolus) during refrigerated storage (2.7°C). Total antioxidant activity of shell extract was determined as 45.84%, total phenolic compound as 17.87 mg/100 g shell, and total carotenoid content in shell as 20.31 mg/100 g shell. Total saturated fatty acid (SFA), monounsaturated fatty acid (MUFA), and polyunsaturated fatty acid (PUFA) contents in the control group and the group with 0.1% shell extract addition were found to be affected by the duration of storage (p < 0.05). A percentage increase was determined in MUFA content, while decreases were observed in PUFA content. No statistically significant change was detected in SFA, MUFA, and PUFA contents of groups with added butylated hydroxytoluene (BHT) and 0.5% of shell extract (p > 0.05). It was concluded that the extract isolated from shrimp shells could be used during the cold storage of fish fillets instead of synthetic antioxidants.     

An Invasive Shrimp Species,Machrobrachium nipponense,in Anzali Wetland Demonstrated a Potential Source for Commercial Fishing

ABSTRACT

The proximate content, fatty acids composition, and nutritional quality index (NQI) of Macrobrachium nipponense at three habitats in the Anzali wetland in Iran were investigated as a potential source for human consumption. The highest amounts of protein, lipid, ash, and energy contents in muscle of M. nipponense were showed in autumn (non-reproductive season) (p < 0.05). The main monounsaturated fatty acids (MUFA) were oleic acid (C18:1 n9 C, C18:1 ω9 T) and palmitoleic acid (C16:1). Moreover, the main polyunsaturated fatty acids (PUFA) were docosahexaenoic acid (DHA, C22:6 n3), eicosapentaenoic acid (EPA, C20:5n3), arachidonic acid (ARA, C20:4 n6), linoleic acid (LA, C18:2 ω6), and α-linolenic acid (ALA, C18:3 n3). The predominant individual saturated fatty acid (SFA) was palmitic acid (0.07–13.4%), while oleic acid (14.7–26.3%), EPA (3.5–12.7%) and linoleic acid (0.04–14.9%) represented the most abundant individual MUFA and PUFA in M. nipponense. The highest mean value of EPA+DHA (14.0), n3/n6 (1.02), ΣMUFA/ΣSFA (1.05), ΣPUFA/ΣSFA (1.04), and EPA/DHA (3.8) ratios in M. nipponense was in autumn. The range of atherogenicity index (AI) and thrombogenicity index (TI) was much lower, from 0.42 to 0.6 and from 0.33 to 0.57, respectively, in terms of season. The results obtained in the present study show that M. nipponense is an excellent nutritional food source in the Anzali wetland.     

Replacement of fish oil with a DHA‐rich Schizochytrium meal on growth performance,activities of digestive enzyme and fatty acid profile of Pacific white shrimp (Litopenaeus vannamei) larvae

This trial was conducted to evaluate the effects of replacing dietary fish oil with Schizochytrium meal for Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Six test microdiets were formulated using Schizochytrium meal to replace 0 g/kg, 250 g/kg, 500 g/kg, 750 g/kg, 1000 g/kg or 1500 g/kg fish oil DHA. No significant differences were observed in survival, growth, final body length and activities of digestive enzyme among shrimp fed different diets (p > .05). No significant differences were observed in C20:5n‐3 (EPA) in muscle samples (p > .05). C18:3n‐3 and C20:4n‐6 in muscle increased as Schizochytrium meal replacement level increased (p < .05). No significant differences were observed in C22:6n‐3 (DHA) and n‐3 fatty acids among shrimp fed diets that algae meal replaced 0 g/kg ‐ 1000 g/kg of fish oil. Shrimp fed diet R150 had higher DHA content than other groups and had higher n‐3 fatty acids than that of shrimp fed diets R50, R75 and R100 (p < .05). C18:2n‐6, PUFA and n‐6 fatty acids in muscle increased, while n‐3/n‐6 ratio decreased with increasing algae meal replacement level from 0 g/kg to 1000 g/kg (p < .05). In conclusion, Schizochytrium meal could replace 1500 g/kg fish oil DHA in the microdiets without negatively affecting shrimp larvae survival, growth and activities of digestive enzyme.     

The contribution of diatoms to bioflocs lipid content and the performance of juvenile Litopenaeus vannamei (Boone, 1931) in a BFT culture system

This study aimed to evaluate the contribution of three diatom species on the lipid content of bioflocs, their permanence on the bioflocs and influence on the growth performance of juvenile shrimps. Juveniles of Litopenaeus vannamei were reared (30 days; three replicates per treatment) in biofloc systems inoculated with diatoms Amphora coffeaeformis (A), Cylindrotheca closterium (C), Conticribra weissflogii (W), or biofloc only (BF, chlorophycean rich). Water quality parameters were monitored daily and the microbiota on days 1, 10, 20 and 30. The lipid content and fatty acid profiles of bioflocs were analyzed at the end of the experiment. Shrimp survival rate (99%) at treatment A was significantly higher than at BF. The bioflocs in A treatment presented the highest lipid content, differing significantly from BF and W. The content of EPA (20:5) (n‐3) was significantly higher in A and lower in BF, while linoleic acid (18:2) (n‐6) was significantly higher in BF. The results indicate that high cell density of diatoms can be successfully maintained with silicate addition in biofloc systems and that the pennate A. coffeaeformis and the centric C. weissflogii are potentially better suited than the pennate C. closterium as food supplements for shrimp diets in biofloc nurseries system.     

The first record of acute hepatopancreatic necrosis disease in the Philippines

A new and emerging disease is threatening the shrimp industry, a bacterial disease which contains a highly pathogenic plasmid, creating a deadly toxin that causes high mortality in shrimps. The disease has been identified as acute hepatopancreatic necrosis disease (AHPND) or commonly known as early mortality syndrome (EMS). To help the efforts of sustaining the shrimp industry, the study focused on detecting Vibrio parahaemolyticus causing AHPND/EMS affecting Penaeus vannamei (Boone, 1931) (Pacific white shrimp) and Penaeus monodon (Fabricius 1798) (Black Tiger shrimp) in different locations in the Philippines. The presence of the disease was determined by microbiological methods and polymerase chain reaction (PCR) and was confirmed by the histopathology of the hepatopancreas of infected shrimp. Results show that the prevalence of the pathogenic strain of V. parahaemolyticus from the shrimps collected were 33% in Luzon, 21% in Visayas and 5% in Mindanao. The study presents the first record of AHPND/EMS in the country. The detection of this newly emerging disease in the shrimp industry is very crucial as it is the first step in identifying affected sites towards strategizing ways to combat the disease.     

THE ARTIFICIAL PROPAGATION AND CULTURE OF BEAR SHRIMP,Penaeus semisulcatus de HAAN,IN HONG KONG

Penaeus semisulcatus (bear shrimp) was used for biological and culture studies. A peak of reproductive periodicity was shown in the months of May, June and July. Increase in body weight and in gonad weight coincided with the increase in sea water temperature. This suggested that sexual maturation might be a direct response to increased sea water temperature. Fecundity of mature female shrimp was estimated as 415,000 to 479,000 ova. In most cases, half-spent spawnings led to the production of poor eggs, characterized by irregular cytoplasmic formation and final autolysis. The embryonic and larval development of P. semisulcatus proceeded satisfactorily in a slightly alkaline medium (pH range from 7.5–8.5), and in water of salinity ranging from 28 to 35 ppt for egg and nauplius stages, and thereafter 25–35 ppt for zoea and mysis stages. The shrimps exhibited faster increase in body length than body weight in early growth. Later, after the shrimps had reached a body length of about 7.0 cm, the growth rate of body weight increased more markedly than body length. The rate of daily increase in weight was 1.01% in 7.0 cm shrimp. The feed efficiency of the formulated shrimp pellets was found to be 31.4%. During the nutritional study of P. semisulcatus, it was found that the combination of high dietary protein (about 40%) and low dietary lipid produced best growth and survival of bear shrimp. High increase of biomass of the shrimp fed with clam meat and high quality fish meal demonstrated the favorable response of shrimp to these diets. The use of cages for culturing bear shrimp was found to be practicable, but not efficient.     

Aurantiochytrium sp. meal as DHA source in Nile tilapia diet,part II: Body fatty acid retention and muscle fatty acid profile

Nile tilapia juveniles (8.35 ± 0.80 g) were fed on four levels (0.0%; 0.5%; 1.0%; 2.0%, 4.0%) of Aurantiochytrium sp. meal (ALL‐G‐RICH?), a source of docosahexaenoic acid (DHA). The 1% Aurantiochytrium sp. meal diet was compared to a control diet, which contained the same amount of DHA as cod liver oil (CLO) at 1.7% diet. Groups of 25 fish were stocked in 100 L tanks and fed twice daily until apparent satiation, for 57 days, at 28°C. Increasing dietary Aurantiochytrium sp. meal reduced the body retention of DHA and n‐3 polyunsaturated fatty acids (n‐3 PUFA) but increased the body retention of alpha‐linolenic (α‐LNA), linoleic (LOA) and n‐6 polyunsaturated fatty acids (n‐6 PUFA). Fatty acid profile in tilapia muscle was affected by increasing dietary inclusions of Aurantiochytrium sp. meal, with an increase in DHA, α‐LNA, n‐3 PUFA and n‐3 long chain‐polyunsaturated fatty acids (n‐3 LC‐PUFA) but a decrease in monounsaturated fatty acids (MUFA), n‐6 PUFA and n‐6 long‐chain polyunsaturated fatty acids (n‐6 LC‐PUFA). There was a larger body retention of DHA, α‐LNA, LOA, n‐3 PUFA and n‐6 PUFA fatty acids and a higher percentage of DHA, n‐3 PUFA and n‐3 LC‐PUFA in muscle fatty acid profile in fish fed on CLO diets than in those fed on 1% Aurantiochytrium sp. Therefore, Aurantiochytrium sp. meal is an alternative source of DHA for Nile tilapia diets.     

硇洲岛周围水域虾拖网虾渔获组成

根据2005年渔业资源监测船生产调查资料和现场取样数据,运用数理统计方法分析了虾拖网虾渔获组成、生物学特征以及月份变化等。结果表明:硇洲岛周围水域虾拖网捕获的虾类主要是沿岸性底栖虾类,渔获中优质虾种少,幼虾比例高,墨吉明对虾、日本囊对虾、哈氏仿对虾是虾拖网渔业的主捕虾种,虾渔获组成存在明显的月份变化。为合理利用虾类资源和促进虾渔业可持续发展,应根据虾类特性开发适宜广东沿海虾拖网的选择性捕捞技术,减少幼虾兼捕量。