Effect of triploidization on juvenile African catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>)

Triploid African catfish (Clarias gariepinus) produced through cold shock 3 min post fertilization were compared to diploid offspring of the same parentage at 66 days of age. Triploid fish were significantly shorter (11%) and weighed less (18%) than diploids but showed no significant difference in mortality or cannibalism, which can be an important source of losses under aquaculture conditions. Erythrocytes of triploid fish were more oval shaped than the normal spherical shape of diploid erythrocytes, were significantly larger (38%) and had nuclei that were significantly larger (25%) than observed in diploid fish. Erythrocyte morphological characteristics show potential as an indicator for the detection of triploidy in African catfish.     

Modulatory effect of lycopene against carbofuran toxicity in African catfish, <Emphasis Type="Italic">Clarias gariepinus</Emphasis>

In the current study, African catfish, Clarias gariepinus, was exposed to a sublethal concentration of carbofuran (CF) to investigate its negative effects on biochemical and oxidative stress biomarkers. Also, the putative role of lycopene (LYC) administration in alleviating these negative effects was evaluated. Fish were divided into six groups in triplicates as follows: group I was without treatment, group II was orally administered corn oil, group III was orally administered 18 mg LYC/kg body weight, group IV was exposed to 0.121 mg CF/L, group V was orally administered 9 mg LYC/kg body weight and exposed to 0.121 mg CF/L, and group VI was orally administered 18 mg LYC/kg body weight and exposed to 0.121 mg CF/L for 4 weeks. At the end of this period, blood and tissue (liver and kidney) samples were collected and biochemical and oxidative stress biomarkers were analysed. Also, histopathological changes were determined. Carbofuran caused significant increments of glucose, cortisol, aspartic amino transferase, alanine amino transferase, cholesterol, urea, and creatinine; meanwhile, serum acetylcholinesterase, total protein, albumin, and total lipids were significantly reduced. Significant increments in hepatic and renal malondialdehyde (MDA) and superoxide dismutase (SOD) levels and marked reduction in hepatic and renal catalase (CAT), glutathione (GSH), and total antioxidant capacity (TAC) levels were observed in CF-exposed fish comparing to the control group. Treatment with LYC attenuated the CF-induced oxidative stress, and this improvement was more pronounced in fish received the high LYC dose (18 mg/kg body weight). Further, congestion of the central vein with infiltration of mononuclear inflammatory cells, vacuolar necrosis, and haemorrhage was observed in the livers of CF-exposed fish. Oral administration of LYC reduced behavioural changes and histopathological alterations. All the altered biochemical parameters and antioxidant biomarkers were also restored to be near the normal levels. The obtained results evoked that LYC administration alleviated the destructive effects of carbofuran and reduced its toxicity effect on African catfish.     

Effects of red clover extract on growth performance and body composition of African catfish <Emphasis Type="Italic">Clarias gariepinus</Emphasis>

ABSTRACT:   The present study was conducted to investigate the effects of the red clover extract on growth, body composition and survival of African catfish Clarias gariepinus . Three concentrations (25, 50 and 75 mg/kg) of red clover at dietary were used for 120 days. The final weights of red clover-treated groups were significantly different from each other and the control group. The best growth was observed in the group receiving the 75 mg/red clover kg diet. Fish fed with all levels of red clover had higher weight gains than the control. The highest values of the specific growth rate and the food conversion rate were 1.14 ± 0.01 and 2.26 ± 0.04, respectively, for the 75 mg/red clover kg diet group. During the red clover administration period, the survival ranged from 97.78% for the 50 p.p.m. group to 95.56% for the 25 and 75 p.p.m. groups. Protein contents of the dosage groups were significantly different from control ( P  < 0.05). The highest value of protein content (19.97%) was observed for the 75 mg/ red clover kg diet. Lipid and ash contents were significantly affected by the red clover levels in the diets. The highest lipid contents were in the 75 mg/red clover kg diet (4.67%), and the highest ash content was 1.39% for the 25 mg/red clover kg diet.     

Laboratory investigation of daily food intake and gut evacuation in larvae of African catfish <Emphasis Type="Italic">Clarias gariepinus</Emphasis> under different feeding conditions

Temporary accumulation of ascorbic acid 2-sulfate (AAS) was measured to estimate food intake and gut evacuation in larvae of African catfish. Fish larvae were fed decapsulated cysts of Artemia containing AAS. In a first experiment it was found that no biosynthesis of AAS occurs in the larvae of this species. In a second experiment, the gut contents of the fish larvae fed were calculated as they changed during development. In a third experiment, the gut evacuation rate of fish larvae was determined during continuous and discontinuous feeding regimes in the first five days after the start of exogenous feeding. Food consumption by catfish larvae increased from 46.5% of their body dry weight (BDW) on day 1 after the start of exogenous feeding to 53.8% BDW on day 3. Thereafter, food consumption decreased to 27.8% BDW on day 5. A similar pattern was observed for gut evacuation, which increased during the first days of exogenous feeding and decreased as fish growth continued. The rate of gut evacuation in a continuous feeding regime was significantly higher (P < 0.05) than that under discontinuous feeding. On day 1 post-hatch and 7 h after first food ingestion the fish larvae evacuated 87% of the food in continuous feeding compared with 43% under discontinuous feeding. It was found that gut emptying differs during larval development. Under continuous feeding, on days 1 and 3 post-hatch and 11 h after the first meal 90% of the food was evacuated compared with 71% evacuated on day 5. The advantages and limitations of the AAS method for estimation of food consumption by fish larvae are discussed.     

Hepatotoxic responses of 4-nonylphenol on African catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>): antixoidant and histochemical biomarkers

4-Nonylphenol (NP) toxicity in fish attracts much attention due to its ability in targeting several organs; however, the researches regarding its potential hepatotoxicity are conflicting and still require further investigation. Therefore, the objective of this study is to focus on this issue from the histophysiological point of view using NP intoxicated African catfish (Clarias gariepinus) as a model of hepatotoxicity. Twelve adult fish (6 per group) were divided into two groups; the first was considered as a control and the second was exposed to NP dissolved in water at a dose of 0.1 mg/kg BW for 3 weeks. A significant reduction in the hepatic alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase levels was observed in NP-exposed fish. Concerning the oxidant/antioxidant balance, a significant depletion in superoxide dismutase, catalase, and glutathione peroxidase was found along with a significant elevation in total peroxide and malondialdhyde. The histopathological examination of the hepatic tissues revealed that NP had marked hepatotoxic effects including hepatitis, centrilobular and focal hydropic and fatty degeneration, fatty change (steatosis), hepatic coagulative necrosis, and nuclear alterations in addition to apoptosis of hepatocytes and necrosis of endothelial cells. Depletion of the glycogen and increased in pigments (lipofuscin and hemosiderin) content in the hepatocytes were also recorded. Hemosiderosis and proliferation of the connective tissue around the blood vessels and branches of bile ducts and in the portal areas were also observed. In light of these findings, it was concluded that NP has a well-defined hepatotoxic impact paving the road towards other studies to investigate other detrimental cyto-physiological influences of this aquatic pollutant.     

Physicochemical and kinetic characteristics of rhodanese from the liver of African catfish <Emphasis Type="Italic">Clarias gariepinus</Emphasis> Burchell in Asejire lake

Two forms of rhodanese were purified from the liver of Clarias gariepinus Burchell, designated catfish rhodanese I (cRHD I) and rhodanese II (cRHD II), by ion-exchange chromatography on a CM-Sepharose CL-6B column and gel filtration through a Sephadex G-75 column. The apparent molecular weight obtained for cRHD I and cRHD II was 34,500 ± 707 and 36,800 ± 283 Da, respectively. The subunit molecular weight determined by sodium dodecyl sulphate–polyacrylamide gel electrophoresis was 33,200 ± 283 and 35,100 ± 141 Da for cRHD I and cRHD II, respectively. Atomic absorption spectrophotometric analysis revealed that cRHD II contained a high level of iron (Fe), which presumably was responsible for the brownish colour of the preparation. In contrast, no Fe was identified in cRHD I, and its preparation was colourless. Further characterization of cRHD II gave true Michaelis–Menten constant (K _m) values of 25.40 ± 1.70 and 18.60 ± 1.68 mM for KCN and Na₂S₂O₃, respectively, an optimum pH of 6.5 and an optimum temperature of 40°C. The Arrhenius plot of the effects of temperature on the reaction rate consisted of two linear segments with a break occurring at 40°C. The apparent activation energy values from these slopes were 7.3 and 72.9 kcal/mol. Inhibition studies on the cRHD II enzyme showed that the activity of the enzyme was not affected by Mn²⁺, Co²⁺, Sn²⁺, Ni²⁺ and NH₄ ⁺, but Zn²⁺ inhibited the enzyme considerably.     

The effect of dietary cricket meal (<Emphasis Type="Italic">Gryllus bimaculatus</Emphasis>) on growth performance,antioxidant enzyme activities,and haematological response of African catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>)

This study was conducted to investigate the growth performance, biomarkers of oxidative stress, catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST) as well as the haematological response of African catfish after being fed with fish feed containing different levels of cricket meal. The juvenile fish were assigned to three different treatments with isonitrogenous (35 %) and isoenergetic (19 kJ g^?1) diets containing 100 % cricket meal (100 % CM), 75 % cricket meal (75 % CM), and 100 % fishmeal (100 % FM) as control groups for 7 weeks. The results indicated that a diet containing 100 % CM and 75 % CM improved growth performance in terms of body weight gain and specific growth rate, when compared to 100 % FM. The feed conversion ratio (FCR) and protein efficiency ratio (PER) did not differ significantly between all diets, but reduced FCR and increased PER were observed with a higher inclusion of cricket meal. A haematological examination of fish demonstrated no significant difference of red blood cells in all diets and white blood cells showed a significantly higher value in fishmeal-fed fish. On the other hand, haemoglobin and haematocrit significantly increased with increasing amounts of cricket meal in the diet. Antioxidant activity of CAT was higher in the 100 % CM group compared to fish fed other diets, whereas GST and SOD showed increasing trends with a higher incorporation of cricket, although insignificant differences were observed between all diets. These results suggest that cricket meal could be an alternative to fishmeal as a protein source in the African catfish diet.     

Bioaccumulation of cadmium and its biochemical effect on selected tissues of the catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>)

The present study examines the pattern of accumulation of cadmium (Cd) and its biochemical effects on selected tissues of a variety of African catfish (Clarias gariepinus), after exposure to various doses of Cd. The results obtained indicate that at the end of 21 days of exposure, the total tissue organ cadmium concentration followed the pattern kidney > gill > liver > muscle for each of the exposure concentrations. The levels of Cd in these organs were higher than those in ambient water. Moreover, while the rate of uptake of Cd increased with time in the kidney, liver and muscle, it decreased in the gill. Superoxide dismutase (SOD) was significantly elevated only in the kidney of catfish treated with 0.2 and 0.4 ppm of Cd for 7 days compared with the control. Conversely, gill SOD was significantly decreased in the same concentrations of Cd-treated catfish relative to the control. Statistically similar levels of SOD were observed in the liver, brain and muscle with all the treatments after the same duration of treatment. In the fish exposed for 21 days, SOD activity was significantly decreased in the kidney with a corresponding increase in lipid peroxidation (LPO), but it manifested only with the 0.2- and 0.4-ppm Cd treatment relative to the control. In the liver, however, Cd exposure significantly increased SOD in the 0.2- and 0.4-ppm treatments of the same duration. In conclusion, the present study indicates that the accumulation of Cd and its effect on SOD and LPO in C. gariepinus is dependent on concentration, tissue and time     

Growth and survival of grouper <Emphasis Type="Italic">Epinephelus</Emphasis><Emphasis Type="Italic">coioides</Emphasis> (Hamilton) larvae fed free-living nematode <Emphasis Type="Italic">Panagrellus redivivus</Emphasis> at first feeding

The free-living nematode, Panagrellus redivivus, was tested as live food for grouper Epinephelus coioides larvae during the first feeding stage. A series of experiments were conducted to determine the acceptability of the free-living nematodes in grouper larvae at first feeding, the optimum nematode density and the response of the larvae to nutritionally enriched nematode. All experiments were conducted in 200-L conical tanks filled with 150-L filtered seawater and stocked at 15 larvae L⁻¹. Duration of feeding experiments was up to day 21 (experiment 1) and 14 days (experiment 2 and 3). Brachionus plicatilis and Artemia (experiment 1) and Brachionus plicatilis alone (experiment 2 & 3) was used as the control treatment. Observations indicated that the grouper larvae readily fed on free-living nematodes as early as 3 days posthatching, the start of exogenous feeding. Optimum feeding density for the larvae was 75 nematodes ml⁻¹. The enrichment of cod liver oil or sunflower oil influenced the total lipids and n-3 highly unsaturated fatty acids of P. redivivus, which in turn influenced those of the grouper larvae, however, growth and survival of the larvae were not affected (P > 0.05). The results from this investigation showed that the nematode, P. redivivus, can be used as first live food for grouper larvae from the onset of exogenous feeding until they could feed on Artemia nauplii.     

Toxicological and hematological effect of <Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract on a freshwater catfish, <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis>

Increasing demand for eco-friendly botanical piscicides and pesticides as replacements for harmful synthetic chemicals has led to investigation of new sources of plant materials. Stem bark of Terminalia arjuna, which has been used as a popular folk medicine since ancient time, was examined for its piscicidal activity. This study aims to determine toxicity of ethanol extract of T. arjuna bark on fresh water stinging catfish (Heteropneustes fossilis), along with evaluation of changes in hematological parameters of the fishes exposed to a lethal concentration. The percent mortality of fishes varied significantly in response to concentrations of the extract and exposure times (between exposure time F = 36.57, p < 0.001; between concentrations F = 39.93, p < 0.001). The lethal concentrations (LC₅₀) of ethanol extract were found to be 12.7, 8.94, 5.63 and 4.71 mg/l for 24, 48, 72 and 96 h, respectively. During acute toxicity test, blood samples of treatment fishes showed significant decreases in the red blood cells count, hematocrit content, hemoglobin concentration, mean corpuscular hemoglobin concentration and plasma protein level when compared to those of the control group, while there were significant increases in the mean corpuscular volume, mean corpuscular hemoglobin, white blood cells count and plasma glucose concentration. These results suggest that T. arjuna bark extract could be considered as a potent piscicide due to its toxic effect on fish, particularly fish hematology.     

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.     

Endocrine disruption,oxidative stress,and testicular damage induced by 4-nonylphenol in <Emphasis Type="Italic">Clarias gariepinus</Emphasis>: the protective role of <Emphasis Type="Italic">Cydonia oblonga</Emphasis>

Exposure to xenoestrogens like 4-nonylphenol (NP) is recognized by disrupting endocrine functions and causes reproductive dysfunction in male fish. The present study aimed at investigating the 4-nonylphenol propensity to induce oxidative stress and hormonal disturbances in male catfish and at studying the protective role of quince (Cydonia oblonga). To fulfill this aim, catfish Clarias gariepinus were exposed to pure 100 μg/L 4-NP and to quince the leaf extract added to 4-NP, both for 15 days. The 4-NP exposure induced a marked increase in 17ß-estradiol (E2), LH, and cortisol, while thyroid hormone (TSH, T3), testosterone (T), and FSH levels noticeably decreased; however, 4-NP had no effect on T4 level. Moreover, 4-NP exposure was accompanied by histological impairments in testes. Existence of 4-NP was associated with oxidative damage as evidenced by the significant increase (p < 0.05) of the enzymes, superoxidase dismutase (SOD), catalase (CAT), acetylcholinesterase (AchE), glutathione s-transferase, total antioxidant capacity (TAC), and malondialdehyde (MDA). Adding quince was effective to neutralize hormonal levels and to repair the testicular histological alterations. In response to quince remedy, the enzymes AchE and MDA reduced significantly (p < 0.05), while limited or no response was detected for other tested enzymes. Our results concluded that quince can antagonize 4-NP toxicity in catfish, confirming that quince leaf extract displayed antioxidant activities against the toxicity of hazardous chemicals.     

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.     

Remarkably high survival rates under dim light conditions in sutchi catfish <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis> larvae

The sutchi catfish Pangasianodon hypophthalmus is an important species for aquaculture in Southeast Asia. However, larvae typically have low survival rates due to their predilection for cannibalism during rearing. This study investigated larval feeding behavior and rearing conditions. The former experiments were performed to elucidate the role of sensory organs in feeding, and the latter experiments examined the effect of dim light on larval rearing and survival rates. Neither lighting conditions (light and dark) nor blocking of free neuromasts by streptomycin had significant effects on feeding behavior. Therefore, the feeding behavior of sutchi catfish larvae most likely depends on chemosensing rather than visual sensing. In the later experiments, larval rearing at 0.1 l× yielded significantly higher survival rates than other lighting conditions (0.00, 1, 10, 100 l×). Survival in the 0.1 l× group was almost three times higher than in the 100 l× group. Moreover, larvae reared under 0.1 l× showed steady growth. Therefore, it is concluded that 0.1 l× is the optimum light intensity for sutchi catfish larval rearing.     

Different carbon sources affects biofloc volume,water quality and the survival and physiology of African catfish <Emphasis Type="Italic">Clarias gariepinus</Emphasis> fingerlings reared in an intensive biofloc technology system

A 6-week experiment was performed to compare different carbon sources, i.e. sucrose, glycerol and rice bran, to a nitrogen ratio of 15:1 in a biofloc-based African catfish Clarias gariepinus culture system. Catfish survival, growth, whole-body proximate composition, body indices, liver histopathology and glycogen content were measured. Each treatment was triplicated in glass aquaria with each replicate containing 50 fish (500 fish/m³) with an initial weight ± SD of 5.06 ± 0.05 g. Glycerol significantly increased total biofloc production, and both the sucrose and glycerol treatments generally had lower nitrogenous levels, compared to the control. These levels spiked at week 2 in the rice bran treatment, leading to significantly lower survival compared to all other treatments. At both weeks 3 and 6, liver histopathology of fish in the rice bran treatment revealed substantial vacuolation and less glycogen while the highest was in fish from the glycerol treatment. Fish growth was unaffected among the treatments, but survival was highest in the glycerol treatment. Rice bran appears unsuitable for C. gariepinus, likely due to being a slower-releasing carbon source. Instead, glycerol is recommended based on significantly higher biofloc production and subsequently improved water quality and survival of C. gariepinus during their nursery culture.     

Demographic and competition studies on <Emphasis Type="Italic">Brachionus ibericus</Emphasis> and <Emphasis Type="Italic">Proales similis</Emphasis> in relation to salinity and algal (<Emphasis Type="Italic">Nannochloropsis oculata</Emphasis>) density

We isolated the rotifers Brachionus ibericus and Proales similis from the sediment of shrimp tanks and studied their individual demographic characters and competition between them at two food levels (0.25?×?10⁶, 1.00?×?10⁶ cells ml^?1 of Nannochloropsis oculata at 25 °C) and salinities ranging from 10 to 30‰. Our hypothesis was that growth rates would be higher with increasing food levels and salinities. Observations were taken twice a day for life table studies and daily once for population growth experiments. Using survivorship and fecundity data, we derived various life history variables. Although the average life span (7.6?±?0.4 days) and gross reproductive rate (33.8?±?2.9 neonate female^?1 day^?1) of B. ibericus were higher than those of P. similis (average life span 5.4?±?0.6 days and gross reproductive rate 13.0?±?0.6 neonate female^?1 day^?1), the population growth experiments showed that P. similis had higher r values (0.32?±?0.005 day^?1) than B. ibericus (0.23?±?0.002 day^?1) at 1.0?×?10⁶ cells ml^?1 of N. oculata. The rotifer P. similis was more adversely affected due to the presence of B. ibericus than vice versa. The data are important for developing techniques for a large-scale culture of these rotifers as food in aquaculture.     

Spatial learning-induced <Emphasis Type="Italic">egr</Emphasis>-<Emphasis Type="Italic">1</Emphasis> expression in telencephalon of gold fish <Emphasis Type="Italic">Carassius auratus</Emphasis>

The immediate-early gene (egr-1) expression was used to examine the neuron’s response in telencephalon of goldfish during spatial learning in small space. Fishes were pre-exposed in the experimental apparatus and trained to pick food from the tray in a rectangular-shaped arena. The apparatus was divided into identical compartments comprising three gates to provide different spatial tasks. After the fish learned to pass through the gate one, two more gates were introduced one by one. Fish made more number of attempts and took longer time (P < 0.05) to pass through the first gate than the gate two or three. This active learning induces the expression of egr-1 in telencephalon as established by western blot analysis. Subsequently, the fish learn quickly to cross the similar type of second and third gate and make fewer errors with a corresponding decline in the level of egr-1 expression. As the fish learned to pass through all the three gates, third gate was replaced by modified gate three. Interestingly, the level of egr-1 expression increased again, when the fish exhibit a high exploratory behavior to cross the modified gate three. The present study shows that egr-1 expression is induced in the telencephalon of goldfish while intensively acquiring geometric spatial information to pass through the gates.     

Effect of combination feeding of <Emphasis Type="Italic">Nannochloropsis</Emphasis> and freshwater <Emphasis Type="Italic">Chlorella</Emphasis> on the fatty acid composition of rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> in a continuous culture

ABSTRACT:   A continuous culture of rotifer was conducted to investigate the effect of combination feeding of both a high density of Nannochloropsis oculata (N) and condensed freshwater Chlorella (FC) on the fatty acid composition of L-type rotifer Brachionus plicatilis in a continuous culture system. The algal feeding of the rotifers was carried out in three successive steps: N-feeding → N+FC-feeding → FC-feeding. The culture was conducted at 24°C and 25–27 psu in a 2000 mL bottle with 50% of water exchanged daily. The combination N+FC-feeding was effective in increasing rotifer density. The rotifers fed on N+FC (N+FC-R) had more non-polar lipids than polar ones, similar to those on N (N-R), opposite to the rotifers fed on FC (FC-R). N+FC-R contained higher levels of 16:2, 18:2n-6 (linoleic acid [LA]) and 20:2n-6, but lower levels of 18:1, 20:4n-6 (arachidonic acid), 20:5n-3 (eicosapentaenoic acid [EPA]) and 22:5n-3 (docosapentaenoic acid [DPA]) compared with N-R. Whereas N+FC-R contained higher levels of 16:1n-7, EPA and DPA, but lower levels of 16:2 and LA compared with FC-R. N+FC-R had more DPA in polar lipids than in non-polar ones. The Σn-6/Σn-3 ratio in N+FC-R was 0.9–1.0, significantly different from those in N-R (0.4) and FC-R (6.6–8.4). Therefore, it is inferred that the fatty acid profile of the N+FC-R cultured in a continuous culture system was affected by both N and FC. Also, the combination N+FC-feeding may be effective in manipulating the Σn-6/Σn-3 ratio in continuously cultured rotifers.     

Digestive enzymes and in-vitro digestibility of different species of phytoplankton for culture of the freshwater pearl mussel, <Emphasis Type="Italic">Hyriopsis</Emphasis> (<Emphasis Type="Italic">Hyriopsis</Emphasis>) <Emphasis Type="Italic">bialatus</Emphasis>

Hyriopsis (Hyriopsis) bialatus has been cultured during the mussel life cycle from glochidia to the adult stage with a low total survival of 6% up to 130-day-old juveniles. The main digestive enzymes (amylase and proteinases) were not detectable in one-day-old juveniles, and increased during development. The stomach, including digestive glands, was the major digestive organ for both carbohydrate and protein. The optimum conditions for amylase activity were 40°C and pH 7; for acidic proteinases they were 60°C and pH 5. Two main alkaline proteinases were found in the intestine, with optimum conditions of 30°C and pH 8 and 60°C and pH 8. To improve mussel survival by finding suitable phytoplankton species and age as food for juveniles and adults, an in-vitro digestibility test was performed on ten algal species three and seven days old using amylase and proteinases in crude enzyme extracts from different mussel life stages. Among the phytoplankton selected, the three most efficiently digested by juveniles were seven-day-old Chlorella sp.2, seven-day-old Chlorococcum sp. and seven-day-old Kirchneriella incurvata, in the ratio 1:1:3 for 30-day-old juveniles and 3:1:1 for 130-day-old juveniles. For the adult mussel, three-day-old Chlorella sp.2, seven-day-old Coccomyxa sp., and seven-day-old Monoraphidium sp., in the ratio 3:1:1, were the most digestible phytoplankton. Levels of in-vitro digestibility were related to the quality (not the concentrations) of carbohydrate and protein in the phytoplankton mixtures, and protein digestibility seemed to be the key factor determining food quality for the mussel.