Effects of dietary l-tryptophan on the agonistic behavior,growth, and survival of freshwater crayfish Astacus leptodactylus Eschscholtz

In this study, the effects of dietary tryptophan (a precursor of 5-hydroxytryptamine, 5-HT, serotonin) on the agonistic behavior, growth, and survival of freshwater crayfish were investigated. For this aim, a control diet (D1) and three experimental diets (D2, D3, and D4) were prepared. D1 contained no additional tryptophan (TRP), but D2, D3, and D4 diets were supplemented with TRP at 0.50, 0.75, and 1.00 % in dry diet, respectively. The control contained 0.33 % TRP. Results revealed that higher supplemental dietary TRP levels caused a significant decrease in the aggressive behavior (P < 0.05), but an increase in the calmness of crayfish. In addition, the results showed that 5-HT levels in the hemolymph before the fight (after 15 days of feeding; resting) were significantly different (P < 0.05) between D1 and D4. There was a significant difference (P < 0.05) in the 5-HT level of hemolymph between the crayfish fed control and D4 after 15 days of feeding. However, after the fight, 5-HT concentration was significantly higher (P < 0.05) in TRP-supplemented A. leptodactylus as compared with the control. The findings of this study showed that supplemental dietary TRP caused a significant increase (P < 0.05) in the growth and survival rate of A. leptodactylus. The crayfish fed D4 had the best survival rate at the end of the experiment (91.60 % in August). The findings of this study also showed that difference in survival rate between the crayfish fed control and D2 in June, July, and August was not significant (P > 0.05). In addition to these, supplemental dietary TRP gave rise to significantly higher specific growth rate (SGR) values in June and July (P < 0.05). For example, in June, it was 0.38 for the crayfish fed D4, 0.28 for the crayfish fed D3, 0.18 for the crayfish fed D2, and 0.13 for the crayfish fed control. However, in August, the highest SGR (0.56) was obtained from the crayfish fed control. The results also showed that the SGRs of females were lower than the males in June, July, and August (P < 0.05). In conclusion, this research shows that the aggressive behavior of A. leptodactylus can be suppressed, and rearing efficiency (i.e., increased growth and high survival rate) of this species can be improved by increasing TRP levels to 1.00 % in its diet.     

Meat yields in the introduced freshwater crayfish, Pacifastacus leniusculus (Dana) and Astacus leptodactylus Eschscholtz, from British waters

The freshwater crayfish industry in Britain is based on two species, Pacifastacus leniusculus (Dana) and Astacus leptodactylus Eschscholtz, which were introduced during the 1970s and 1980s. The former is widely cultivated but both are also established in the wild, from where they are harvested. Very few studies have been made of the meat yield in these two species and none on British populations. Two essentially wild populations were assessed for their meat yield. Due to its more massive claws male P. leniusculus had a higher meat yield than male and female A. leptodactylus and female P. leniusculus in both winter and summer months. Less difference was found between the yield of tail meat between the sexes and species. Compared with other studies, meat yield in the two British populations of P. leniusculus (11–15%) and A. leptodactylus (9–13%) would appear to be lower; possible reasons for this are discussed. However, expressing meat yield as a percentage of wet body weight, although useful for comparative purposes, can give conflicting results – examples of this are given. Meat yields from the claws of the two species indicated that positive allometric growth continued after sexual maturity.     

Incisor ridge modification of the mandibles in freshwater crayfish, Astacus leptodactylus

The differences in the ridge structure of the mandibles of different size Astacus leptodactylus (32–80 mm carapace length, CL) were investigated. The results showed that a modification occurs with an increase in size in the incisor ridge of mandibles in A. leptodactylus. The results also showed that A. leptodactylus possesses four different types of ridge structure in the mandibles. These are: (1) Incisor ridge with big teeth (dentate crenate), (2) Blade-like incisor ridge with numerous small teeth, (3) Blade-like ridge (toothless), (4) Blunt ridge. In conclusion, it is thought that the incisor ridge modification of the mandibles may cause the difference in the food choice of different size A. leptodactylus, because, crayfish possessing different ridge structures of the mandible may probably feed on different type of food.     

The effect of dietary vitamin E on the pleopodal egg number of Astacus leptodactylus (Eschscholtz, 1823)

The effect of vitamin E on the pleopodal egg number of Astacus leptodactylus (Eschscholtz, 1823) was studied. Crayfish were fed 2% of their total wet weight daily with vitamin E supplemented diets and a control for 70 days. The vitamin E content of the control diet, diet 1, diet 2 and diet 3 were 20 mg kg^–1, 40 mg kg^–1, 80 mg kg^–1 and 160 mg kg^–1 respectively on a dry weight basis. Vitamin E levels of the control and experimental diets were analysed by High Performance Liquid Chromatography. Results showed that diets containing supplemental vitamin E were associated with an increase in the number of pleopodal eggs. The best result was obtained with diet 2 containing 80 mg kg^–1 supplemental vitamin E.     

A comparison of the growth and survival of two freshwater crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), under different temperature and density regimes

Growth experiments carried out with two juvenile crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), at different temperatures and densities highlighted the problem of cannibalism under conditions aimed at intensifying crayfish production. Cannibalism proved to be much lower in A. leptodactylus than P. leniusculus, suggesting that the former might be the better candidate for astaciculture. In the first of two population survival trials, A. leptodactylus showed a higher survival rate than P. leniusculus, with 26% of P. leniusculus surviving in the first replicate, compared to 42.3% of P. leniusculus, and 40.76% surviving in the second replicate, compared to 47.6% of P. leniusculus. The same trend was observed in the second experiment, with P. leniusculus showing survival rates of 48.5 and 55.3% (first and second replicates, respectively) in comparison to 65.2 and 68.2%, respectively, for A. leptodactylus. It is therefore highly likely that if P. leniusculus were to become established in Turkey, it would outcompete the native A. leptodactylus even if it were not to be devastated by the crayfish plague that has decimated the native species. The experiments also highlighted the problem of differential growth, with some juveniles hardly growing at all while others reached a relatively large size. The range in carapace length (CL) was 9–18 mm for A. leptodactylus and 8.5–18.5 mm CL for P. leniusculus at the end of the first experiment. While both species grew quickly, P. leniusculus hatched earlier, giving it an advantage over A. leptodactylus; consequently, by the end of the summer, the juveniles of the former were larger than those of A. leptodactylus. Specific growth rate values showed that the juveniles of the two species had similar growth rates. The results also revealed that growth was not significantly affected by density in both species at 15°C, but at 25°C, growth was significantly better at a density of 234 juveniles m⁻² than at 468 juveniles m⁻², and better at 468 juveniles m⁻² than at 937 juveniles m⁻² (P < 0.01 and P < 0.001, respectively). We conclude that P. leniusculus is a good candidate for aquaculture as it has a rapid growth rate and early hatching and maturity; however, its aggressive behavior may make it a less attractive proposition than A. leptodactylus, which is also fast growing but less aggressive. This study is a part of PhD study of M.M. Harlıoğlu, who is supported by Fırat University Elazığ, Turkey.     

The present situation of freshwater crayfish, Astacus leptodactylus (Eschscholtz, 1823) in Turkey

The only native crayfish species in Turkey, Astacus leptodactylus, is widely distributed in lakes and ponds in many parts of the country. Its distribution area was considerably expanded in Turkey after 1985 because of its commercial importance and declined catches from traditional good fisheries. Although consumption of A. leptodactylus has always been very low in Turkey, it was exported to western Europe until 1986. Due to over-fishing, pollution and a disease (crayfish plague), the total production decreased dramatically to 200 from 5000 tonnes annually. In recent years (1991–1998), there has been a gradual increase in the production of crayfish in Turkey from 320 to 1500 tonnes, but plague is still present.     

The effect of darkness on mating and pleopodal egg production time in a freshwater crayfish, <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz

In the present study, the effect of darkness on the timing of mating and pleopodal egg production in Astacus leptodactylus was investigated. Crayfish were exposed to three different light regimes: natural day light regime (control, mean 10.04-h light/13.96-h dark); 24-h dark (24 h D); 8-h light/16-h dark (8 L:16 D). Experiments were carried out between November 2006 and January 2007 with 36 males and 144 females. The results showed that darkness did not have an effect on the onset of mating and pleopodal egg production in the groups, but it did affect significantly the timing of individual matings; the higher percentage of ovigerous females in the darkness group at the first observation means that on average females under this condition mated and spawned earlier than in the other groups (P < 0.01). The percentage of ovigerous females exposed to constant darkness in the first observation in which crayfish started to mate and spawn was 62.50. These figures for those exposed to 16 D:8 L and control were 43.75 and 37.50%, respectively. Therefore, it can be concluded that the reproduction efficiency (i.e., rate of ovigerous females) of A. leptodactylus can be enhanced under controlled conditions by exposing broodstock to constant darkness in their mating and spawning season.     

细鳞鲑幼鱼n-3 HUFA需求量的研究

为确定细鳞鲑(Brachymystax lenok)n-3 HUFA需求量以减少鱼油使用和降低养殖成本,研究饲料中不同水平的n-3 HUFA对细鳞鲑的生长性能、体成分和肌肉脂肪酸组成的影响。以脱脂鱼粉、脱脂豆粕、明胶和酪蛋白为主要蛋白源,通过调节饲料中的猪油和浓缩油EPA、DHA水平,使饲料n-3HUFA的含量分别达到0.25%、0.50%、0.75%、1.00%、1.25%、1.50%,配制出6种等氮等能的试验饲料(D 0.25、D 0.50、D 0.75、D1.00、D 1.25和D 1.50),分别投喂细鳞鲑幼鱼(60.0 g±2.8 g)84 d。结果显示:饲料中n-3HUFA不同水平对细鳞鲑成活率和饲料系数没有显著影响,但是显著影响了其末重(FW)、增重率(WGR)和特定生长率(SGR)。随着添加饲料中n-3HUFA水平的升高,FW、WGR和SGR有先升高后下降的趋势,且3者在饲料中n-3HUFA水平为0.75%均最大。随着饲料中n-3 HUFA水平的升高,鱼肌肉18∶1n-9的含量逐渐下降,而22∶6n-3的水平相应升高。结果表明,以WGR为评价指标时,用二次曲线模型推测出细鳞鲑对饲料n-3 HUFA的需求量约为0.69%。     

A preliminary study on the use of mannan oligosaccharides (MOS) in freshwater crayfish, <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz, 1823 juvenile diets

The effects of dietary mannan oligosaccharides (MOS) on the survival and growth of Astacus leptodactylus juveniles were evaluated. Experimental diets were prepared by using supplementation of 0 (Control), 1.5, 3.0, and 4.5 g MOS kg⁻¹ commercial trout larvae diet containing 43 g kg⁻¹ protein and 15.74 g kg⁻¹ lipid. A. leptodactylus juvenile with an average total length of 3.6 ± 0.46 cm (TL) and average weight of 1.25 ± 0.43 g was stocked in 0.2-m² aquariums at a rate of 50 crayfish/m² and reared for 60 days at 22.8°C. The experiment consisted of four treatments with three replicates each. Each aquarium contained ten crayfish. Crayfish juvenile fed with 0, 1.5, 3.0, and 4.5 MOS attained 6.15 ± 0.49, 5.94 ± 0.29, 7.34 ± 0.39, and 5.94 ± 0.27 cm final total length and 50, 56.67, 46.67, and 50% survival rates, respectively. Moreover, molting frequencies in 0, 1.5, 3.0, and 4.5 g kg⁻¹ MOS groups were detected as 44.44, 61.11, 83.33, and 38.88%, respectively. At the end of the experiment, a general enhanced growth performance (P < 0.05) and feed conversion ratio were observed in crayfish fed on the diet containing 3.0 g kg⁻¹. Crayfish juveniles fed with 3.0 g kg⁻¹ MOS had the highest final length (7.34 ± 0.39 cm), although their survival was the lowest (46.67%) compared to other treatments but not significant. Specific growth rates were significantly different (P < 0.05) among the treatment groups at the end of the 60-day experiment. There were no significant differences (P > 0.05) in percentage moisture, protein, and ash (wet-weight basis) in the tail meat of A. leptodactylus juvenile among treatments (diet) that averaged 82.3, 16.1, and 1.2%, respectively. However, lipid value was significantly different among the diets P < 0.05), with values between 0.13 and 0.32. From the current results, it could be advised to use MOS at the rate of 3.0 g kg⁻¹ in A. leptodactylus juvenile diets.     

Essential fatty acids in Atlantic salmon: effects of increasing dietary doses of n-6 and n-3 fatty acids on growth, survival and fatty acid composition of liver, blood and carcass

Atlantic salmon fry (4 g) were fed for 4 months on semi-synthetic diets containing fatty acid methyl esters of either 18:2 n-6, 18:3 n-3 or a mixture of equal amounts of 20:5 n-3 and 22:6 n-3. The different amounts of polyunsaturated fatty acids added were 0, 0.1, 0.2, 0.5, 1 and 2% (by dry weight). Increasing levels of dietary n-3 fatty acids up to 1% gave faster growth rates in salmon fry, and fish fed the mixture of 20:5 n-3 and 22:6 n-3 seemed to grow faster than fish fed only 18:3 n-3. No significant effect on growth rate was seen when the dietary level of 18:2 n-6 was increased. Dietary inclusions of n-3 fatty acids reduced the mortality of salmon, while dietary 18:2 n-6 had no such beneficial effects.
The dietary treatments caused substantial changes in the fatty acid composition of blood and liver phospholipids (PL), whereas the total lipid fraction of the carcass was less affected. Increasing doses of 18:2 n-6 in the diet resulted in an increased percentage of 20:4 n-6 in liver and blood PLs, while the percentage of 20:3 n-9 decreased. The percentage of 18:2 n-6 also increased in liver, blood and carcass. Dietary 18:3 n-3 resulted in increased percentages of 18:3 n-3 and 20:5 n-3 in liver PLs, while the percentage of 20:3 n-9 decreased. There was, however, no significant increase in the percentage of 22:6 n-3. Dietary 18:3 n-3 produced no significant changes in the composition of blood fatty acids, but increased the percentage of 18:3 n-3 in the carcass. The dietary combination of the n-3 fatty acids 20:5 and 22:6 resulted in an increased percentage of 22:6 n-3 in blood and liver lipids and a decreased percentage of 20:3 n-9, but there were no changes in the percentage of 20:5 n-3.     

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.     

Effects of dietary (n-3) and (n-6) polyunsaturated fatty acid ratio on the immune response of Atlantic salmon, Salmo salar L.

To examine the influence of the dietary ratio of (n-3) to (n-6) polyunsaturated fatty acids (PUFAs) on the immune system of Atlantic salmon, Salmo salar L., two dietary trials were carried out in which parr were maintained on diets containing either fish oil [(n-3)/(n-6) PUFA = 5.2] or sunflower oil [(n-3)/(n-6) PUFA = 0.3] and assessed for differences in immunological parameters. There were no significant differences in blood cell counts, differential leucocyte counts or haematocrit values between dietary groups, and while no apparent differences were observed in the non-specific immune parameters measured, there was a significantly higher number of B cells responding to Aeromonas salmonicida, in the kidney and spleen of vaccinated fish maintained on high (n-3)/(n-6) PUFAs diets. There was also a significant difference (P≤ 0.01) between the dietary groups in trial 1 and trial 2 when non-vaccinated fish were challenged with Aeromonas salmonicida and Vibrio anguillarum, respectively, with the (n-6) group succumbing to the bacterium before the (n-3) group. The results suggest that Atlantic salmon fed diets with a low ratio of (n-3)/(n-6) PUFA may be less resistant to infection than those fed diets containing lipid with a high (n-3)/(n-6) PUFA ratio.     

Polyunsaturated fatty acid metabolism in cultured fish cells: Incorporation and metabolism of (n-3) and (n-6) series acids by Atlantic salmon (Salmo salar) cells

The incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids (PUFA) supplemented to growing cultures were studied in Atlantic salmon (AS) cells. A fatty acid concentration of 25 μM considerably altered the fatty acid composition of AS cells without increasing the neutral lipid content of the cells or inducing the production of cytoplasmic lipid droplets. Whereas Δ6 and Δ5 desaturase activities were significantly expressed in AS cells, Δ4 desaturase activity was very low. Both the Δ6 desaturase activity and the Δ5 desaturase activity showed some preference for (n-3) PUFA.     

The harvest of the freshwater crayfish <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz in Turkey: harvest history,impact of crayfish plague,and present distribution of harvested populations

This review focuses on the present distribution of populations of the crayfish Astacus leptodactylus that are harvested in Turkey. It also examines the history of this harvest and the impact that crayfish plague has had on them. Crayfish plague, caused by the fungus-like organism, Aphanomyces astaci Schikora, 1906, is a severe parasite of freshwater crayfish and has caused a lot of damage to A. leptodactylus populations in Turkey since 1984. Turkey was the largest provider of A. leptodactylus to Western Europe from 1970 (or possibly earlier) until 1986. For example, the peak production was reached in the early 1980s, with over 5,000 tonnes being exported in 1984. On the other hand, as a result of the crayfish plague the harvest of A. leptodactylus was reduced severely in most populations in Turkey after 1985. The harvest was only 320 tonnes in 1991. After the occurrence of crayfish plague in Turkey, in order to increase crayfish production uncontrolled A. leptodactylus stockings have been carried out in many waterbodies throughout Turkey. These introductions have caused an increase in the number of A. leptodactylus populations, but exploitation of A. leptodactylus is still under the pressure of the plague, although there has been a steady increase in crayfish production in recent years. The harvest increased to 2,317 tonnes in 2004. Fortunately, among those populations affected by crayfish plague, large amounts of A. leptodactylus can still be harvested from three lakes, ?znik (Bursa), E?irdir (Isparta) and Çivril (Denizli). Thus, it seems that A. leptodactylus has a degree of resistance to crayfish plague. It is therefore interesting to investigate the resistance of A. leptodactylus caught from these populations to crayfish plague.     

Effect of salinity on the biosynthesis of n-3 long-chain polyunsaturated fatty acids in silverside Chirostoma estor

The genus Chirostoma (silversides) belongs to the family Atherinopsidae, which contains around 150 species, most of which are marine. However, Mexican silverside (Chirostoma estor) is one of the few representatives of freshwater atherinopsids and is only found in some lakes of the Mexican Central Plateau. However, studies have shown that C. estor has improved survival, growth, and development when cultured in water conditions with increased salinity. In addition, C. estor displays an unusual fatty acid composition for a freshwater fish with high docosahexaenoic acid (DHA)/ eicosapentaenoic acid (EPA) ratios. Freshwater and marine fish species display very different essential fatty acid metabolism and requirements, and so the present study investigated long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis to determine the capacity of C. estor for endogenous production of EPA and DHA, and the effect that salinity has on these pathways. Briefly, C. estor were maintained at three salinities (0, 5, and 15 ppt), and the metabolism of 1?C-labeled 18:3n-3 was determined in isolated hepatocyte and enterocyte cells. The results showed that C. estor has the capacity for endogenous biosynthesis of LC-PUFA from 18-carbon fatty acid precursors, but that the pathway was essentially only active in saline conditions with virtually no activity in cells isolated from fish grown in freshwater. The activity of the LC-PUFA biosynthesis pathway was also higher in cells isolated from fish at 15 ppt compared with fish at 5 ppt. The activity was around fivefold higher in hepatocytes compared with enterocytes; although the majority of 18:3n-3 was converted to 18:4n-3 and 20:4n-3 in hepatocytes, the proportions of 18:3n-3 converted to EPA and DHA were higher in enterocytes. The data were consistent with the hypothesis that conversion of EPA to DHA could contribute, at least in part, to the generally high DHA/EPA ratios observed in the tissue lipids of C. estor.     

Incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids in phospholipid classes in cultured turbot (Scophthalmus maximus) cells

The incorporation and metabolism of various (n-3) and (n-6) polyunsaturated fatty acids (PUFA) supplemented to the culture medium was investigated in a turbot cell line (TF). The distribution, and the occurrence and extent of further metabolism of incorporated PUFA via desaturation/elongation mechanisms in specific phospholipid classes was determined from the different fatty acid compositions. The cells contained Δ6 and Δ4 desaturase activities but were generally deficient in C18–20 elongase activity. Δ5 Desaturase activity was generally masked by this deficiency but was present. The compositional data indicated that there was a high degree of specificity between individual phospholipid classes and particular fatty acids probably driven by the specificities of the acylating enzymes. The highest percentages of the supplemented acids were generally observed in the phosphatidic acid/cardiolipin fraction (PA/CL), suggesting a role for PA in the incorporation of the supplemented acids into the phospholipid pool. PI had a characteristic composition consistent with a putative role as a pool of precursor fatty acid for eicosanoid synthesis. Mechanisms were evident for generating and/or maintaining this composition.     

Effect of dietary protein level on growth and survival of juvenile freshwater crayfish Cherax quadricarinatus (Decapoda: Parastacidae)

Protein requirements of juvenile freshwater crayfish Cherax quadricarinatus, with initial mean weight of 1.08 ± 0.34 g, were studied. Juveniles were fed experimental diets containing seven levels of crude protein (CP) (20, 25, 31, 37, 43, 49, and 55%) and 18.73–21.45 kJ  g^?1 of gross energy. The highest mean weight and specific growth rate (SGR) (P < 0.05), with values of 9.6 g, and 3.64% day^?1, respectively, were achieved by feeding a diet of 31% CP. This diet resulted in a survival rate of 80% over 60 days of culture at 27 °C. The higher protein level tested (55% CP), yielded a significantly (P < 0.05) lower mean weight of 6.4 g. However, there were no significant differences in SGR among the 20, 25, and 49% CP diets. Feed Conversion Ratio (FCR) was close to 1 for all treatments except the lowest (20%) and highest (55%) CP. Optimum protein requirements were estimated by fitting mean weight gain data to a quadratic model (y = 1.142+0.484 ? 0.0071x², r² = 0.952, P < 0.05). Optimal growth occurred with 34.2% CP, but the results suggest that optimum protein level for 1‐g juvenile C. quadricarinatus is 31% in least‐cost diets. The information obtained will contribute to the formulation of diets that will enhance production of C. quadricarinatus.     

Incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids in phospholipid classes in cultured rainbow trout (Salmo gairdneri) cells

The incorporation and metabolism of various (n-3) and (n-6) polyunsaturated fatty acids supplemented to the culture medium was investigated in the rainbow trout cell line, RTG-2. The distribution, and the occurrence and relative extent of further desaturation and elongation of the incorporated acids was determined in individual phospholipid classes by analysis of the fatty acid compositions. RTG-2 cells exhibited Δ6 and Δ5 desaturase activities whereas Δ4 desaturase activity was almost totally absent. The percentage of precursor acids was greatest in the phosphatidic acid/cardiolipin fraction (PA/CL), suggesting a role for possibly PA in the initial incorporation of these acids into the phospholipid pool. The compositional data indicated that individual intermediates and products of the desaturation pathways were associated with specific phospholipid classes probably via mechanisms depending upon the specificities of the acylating enzymes. The composition of phosphatidylinositol (PI) and the tightly controlled mechanisms for generating/maintaining it are consistent with a role for this phospholipid in providing precursor fatty acid for eicosanoid synthesis.     

Effect of dietary protein level on the growth and survival of pre-adult freshwater crayfish Cherax quadricarinatus (von Martens) in monosex culture

Feeding trials with five levels of crude protein (CP) (22%, 27%, 33%, 39%, and 45%) and digestible energy ranging from 14.32 to 15.21 kJ g^?1 were carried out to determine optimum dietary protein for the growth and production of pre‐adult freshwater crayfish Cherax quadricarinatus. Triplicate groups of males (ω=23.1±0.58 g) and females (ω=21.8±0.33 g) were fed diets for 70 days in monosex culture. Optimal digestible protein (DP) was estimated for males by fitting mean weight gain to a quadratic model (y=27.86+0.839x–0.0216x², r²=0.945), and a linear model for females (y=32.84–0.0745x, r²=0.959). Optimal male growth occurred with 25.6% CP, equivalent to 19.4% DP. Male crayfish attained significantly higher final weights and absolute growth rate than females fed the 22%, 27%, and 33% CP diets. The results indicated that a 19.4% DP diet, with a P/E ratio of 11.4 mg kJ^?1, produces an optimum growth response for pre‐adult C. quadricarinatus under experimental conditions.