Enrichment of Artemia nauplii with the probiotic yeast Saccharomyces boulardii and its resistance against a pathogenic Vibrio

Enrichment of Artemia nauplii with a known probiotic yeast Saccharomyces boulardii (SB) and its role in enhancing resistance against the pathogen Vibrio harveyi was investigated. SB was cultured, then fed to instar II Artemia nauplii in three different treatments; 10² (T1), 10³ (T2) and 10⁴ (T3) colony forming units (CFU) per ml in triplicate. The algae Nanochloropsis sp. was used as control diet. Survival and total count of CFU nauplii⁻¹ was observed on different media (Sabouraud, for enumerating yeasts, thiosulphate citrate bile salts sucrose, for enumerating Vibrio and seawater agar, for enumerating total aerobic flora) for each replication. Enhanced survival of nauplii was observed in treatments as compared to control. Results indicated that enrichment of SB in Artemia nauplii proceeded in a linear fashion, and up to 3500 CFU of SB could be detected in one nauplii at 10⁴ CFU ml⁻¹ treatment. No conclusive trend could be observed in the count of Vibrio and total aerobic flora due to treatment. Enriched nauplii were then challenged with the pathogen V. harveyi for 24 and 48 h at a concentration of 6.1 × 10⁶ CFU ml⁻¹. The survival counts at 48 h showed that the resistance of the nauplii was significantly (P < 0.01) improved in those fed with 10⁴ CFU  ml⁻¹ SB (90% survival rate after 48 h of challenge versus less than 40% for the infected control group without SB and treatments T1 and T2). This study shows that SB, which has been used for the first time in an aquatic live feed organism, has a profound beneficial effect on the nauplii by increasing its resistance to a pathogenic Vibrio infection. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> L.) larvae rearing under controlled conditions: density and basic supply of <Emphasis Type="Italic">Artemia</Emphasis> nauplii as the sole food

After artificial reproduction of tench, larvae must be maintained indoors, and studies on rearing conditions are needed, focussing on the reduction of labour and costs. Three experiments on larvae (5th day post-hatch) were conducted for 25 days using Artemia nauplii as the sole food in order to determine basic feeding and density conditions during the first rearing period. Tench were maintained in 25 l fibreglass tanks, supplied with an artesian water flow throughout of 0.2 l min⁻¹. Water temperature was 22.5 ± 1°C, and the photoperiod was natural. Larvae fed on a restricted amount of nauplii reached high survival rates, even with the minimum of 50 nauplii larva⁻¹ day⁻¹. This amount of food may be sufficient at least for the first 25 days of exogenous feeding if fast growth is not the priority, and high densities can be maintained with good survival rates (over 90% up to 160 larvae l⁻¹ and 77% with 320 larvae l⁻¹). When food was supplied in excess once a day, high survival rates were achieved (91–97%), without differences among the densities tested. Animals at a density of 100 l⁻¹ reached the highest length (15.57 mm) and individual weight (46.8 mg). This growth is greater than those reported in studies feeding several times a day. It could be deduced that, while live food remains available for tench, it is not necessary to feed so frequently. Considering the relationship among the initial number of animals, final survival and growth and ration supplied, the new data reported here are useful to establish suitable stocking densities under both culture and experimental conditions.     

Studies on digestibility and digestive enzyme activities in Labeo rohita (Hamilton) juveniles: effect of microbial α-amylase supplementation in non-gelatinized or gelatinized corn-based diet at two protein levels

A 60-days feeding trial was conducted to delineate the effect of both gelatinized and non-gelatinized corn with or without supplementation with exogenous α-amylase at two dietary protein levels (35% and 28%) on dry matter digestibility, digestive enzymes and tissue glycogen content of Labeo rohita juveniles. Three hundred and sixty juveniles (average weight 10±0.15 g] were randomly distributed into 12 treatment groups with each of two replicates. Twelve semi-purified diets containing either 35% or 28% crude protein were prepared by including gelatinized (G) or non-gelatinized (NG) corn as carbohydrate source with different level of microbial α-amylase (0, 50, 100 and 150 mg kg⁻¹). The dry matter digestibility of G corn fed groups was significantly higher (P < 0.05) than that of the NG corn fed groups. Hepatosomatic index (HSI), liver glycogen and intestinal amylase activity of G starch fed groups were significantly higher (P < 0.05) than those of the NG corn fed groups. However, the reverse trend was found for gastrosomatic index (GSI), muscle glycogen and intestinal protease activity. Addition of 50 mg α-amylase kg⁻¹ feed improved the dry matter digestibility of NG starch fed groups, which was similar to that of the G corn fed groups or NG corn supplemented with 100/150 mg α-amylase kg⁻¹ feed. HSI, liver glycogen and intestinal amylase activity were significantly increased (P < 0.05) at minimum level of α-amylase in the feed (50 mg kg⁻¹) and did not increase due to further inclusion of amylase in the diet. Supplementation with α-amylase at 50 mg kg⁻¹ increased the intestinal amylase activity beyond which no significant changes were observed. Protease activity of liver and intestine was highest (P < 0.05) in higher crude protein (CP) fed groups, but protease activity of the intestine was significantly higher in the α-amylase supplemented groups. Hence, it was concluded that feed with 28% CP containing either G corn without α-amylase or NG corn with 50 mg α-amylase kg⁻¹ may be used as the alternative carbohydrate source for L. rohita juveniles.     

The influence of feeding rate on growth, feed efficiency and body composition of juvenile grass carp (Ctenopharyngodon idella)

An 8 weeks growth study was conducted to estimate the optimal feeding rate for juvenile grass carp (3.08±0.03 g, mean ± SD). Fish were fed with a casein purified diet (360 g protein, 56 g lipid and 3000 kcal total energy/kg dry diet) at six feeding rates: 1.0, 1.5, 2.0, 2.5, 3.0, 3.5% body weight per day (BW d⁻¹). Each feeding rate was randomly assigned to three tanks of fish with 30 fish per tank (50W × 50H × 100L, cm). Fish were maintained in recirculating systems at a water temperature of 24.97±2.23 °C and were fed four times per day. After 2 weeks, fish fed on 3.5% BW d⁻¹ could not finish the diet and this treatment was cut-off. Analysis of variance showed that growth performance was significantly (p<0.05) affected by different feeding rates. The nutrient compositions of whole body, muscle and liver were also significantly different among treatments. The body weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), apparent digestibility coefficiency (ADC), retention of protein (PR), mesenteric fat index, body moisture and protein content were significantly (p<0.05) affected by feeding rate. The WG, SGR and digestion rate were highest at 2% BW d⁻¹, although the FE and PER decreased with increasing feeding rate. Broken line analysis on specific growth rate indicated that the optimum feeding rate of juvenile grass carp is 1.97% body weight day⁻¹.     

Effect of a probiotic bacterium <Emphasis Type="Italic">Bacillus circulans</Emphasis> PB7 in the formulated diets: on growth,nutritional quality and immunity of <Emphasis Type="Italic">Catla catla</Emphasis> (Ham.)

Bacillus circulans PB7, isolated from the intestine of Catla catla, was evaluated for use as a probiotic supplement in the feeds for the fingerlings of Catla catla. The effect of supplement on the growth performance, feed utilization efficiency, and immune response was evaluated. Catla fingerlings (ave. wt. 6.48 ± 0.43 g) were fed diets supplemented with 2 × 10⁴ (feed C1), 2 × 10⁵ (feed C2), and 2 × 10⁶ (feed C3) B. circulans PB 7 cells per 100 g feed for 60 days at 5% of the body weight per day in two equal instalments in triplicate treatments. The control feed (CC) was not supplemented with the B. circulans. All the feeds were isocaloric and isonitrogenous. Fish fed with feed C2 displayed better growth, significantly (P ≤ 0.05) highest RNA/DNA ratio, a lower feed conversion ratio (FCR), and a higher protein efficiency ratio (PER) than the other experimental diets. Highest carcass protein and lipid was also observed in the fish fed C2 feed compared to the others. Significantly (P ≤ 0.05), highest protease was recorded in fish fed feed C2 (47.9 ± 0.016) and lowest in fish fed feed C3 (32.10 ± 0.009), where α-amylase activity did not differ significantly (P ≤ 0.05) beyond the lowest inclusion level. ALP, ACP, GOT, and GPT in the liver of Catla catla were the highest (P ≤ 0.05) in fish fed C2 feed. The highest TSP, albumin, and globulin was observed in fish treated with C2 feed after 60 days feeding trial, but the lowest glucose level was observed in the same treatment. After the feeding trial, the non-specific immunity levels and disease resistance of fish were also studied. Phagocytic ratio, phagocytic index, and leucocrit value were the highest in fish fed feed C2. After the feeding trial, the fish were challenged for 10 days by bath exposure to Aeromonas hydrophila (AH1) (10⁵c.f.u. ml⁻¹ for 1 h, and, after 7 days, 10⁷c.f.u. ml⁻¹ for 1 h). Highest survival percentage was observed in fish fed with feed C2 compared with only 6.66% in the controls, which indicated the effectiveness of B. circulans PB 7 in reducing disease caused by A. hydrophila.     

Bioaugmentation in the growth and water quality of livebearing ornamental fishes

Bacillus subtilis isolated from the intestine of Cirrhinus mrigala (Hamilton) was incorporated into the rearing water of Poecilia reticulata (Peters), Poecilia sphenops (Valenciennes), Xiphophorus helleri (Heckel) and Xiphophorus maculatus (Gunther) at four different concentrations (5 × 10⁸ cells ml⁻¹, 5 × 10⁷ cells ml⁻¹, 5 × 10⁶ cells ml⁻¹ and 5 × 10⁵ cells ml⁻¹) and its effect on fish growth performance and survival, water quality parameters and bacterial population of water were assessed. The results showed that the addition of bacterial cells in the rearing water resulted in greater survival and a faster growth rate and, hence, greater length and weight increments of the livebearers. The use of a bioaugmentor in the rearing water of the livebearing fishes resulted in significantly lower (P < 0.05) concentrations of dissolved organic matter and total ammonium nitrogen. The counts of motile aeromonads and total coliforms recorded in the water of bioaugmented tanks were also lower than that in the control tank. Bioaugmentation between 10⁶ and 10⁸ cells ml⁻¹ in the rearing water is sufficient in establishing a bioaugmentor and the use of a higher concentration of bacterial cells did not always lead to significantly better results.     

Use of vitamin C as an immunostimulant. Effect on growth,nutritional quality,and immune response of <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.)

Teleost fish lack the enzyme for endogenous synthesis of ascorbic acid (AA), an essential micronutrient for fish. The aim of this study was to examine the effect of higher levels of dietary vitamin C on growth, nutritional quality, and immunomodulation in the Indian major carp, rohu (Labeo rohita). Four groups of L. rohita were fed experimental diets containing either no vitamin C (control) or supplemented with vitamin C at 500 mg kg⁻¹ (Exp-1), 1000 mg kg⁻¹ (Exp-2), or 1500 mg kg⁻¹ (Exp-3) for 60 days. Growth parameters (NWG, ADG, and SGR), serological parameters (TSP, TSA, TSG, and A:G), haematological parameters (TLC, TEC, Hct, MCV, and MCH), and different non-specific immunological parameters (PR, PI, respiratory burst activity, and bactericidal activity) were evaluated during the experimental trial. Fish fed a vitamin C-supplemented diet showed higher specific growth rate (SGR) up to 1000 mg kg⁻¹ compared with control fish. Different haematological and serological parameters along with non-specific immune parameters were influenced by vitamin C supplementation. Among the non-specific immune parameters phagocytic activity (PR and PI) and respiratory burst activity (NBT cells) were significantly (P ≤ 0.05) enhanced by increasing doses of vitamin C supplementation. Higher levels of dietary vitamin C significantly (P ≤ 0.05) enhanced protection against Aeromonas hydrophila (AH1) infection compared with controls. Results from this study help to establish the beneficial effect of vitamin C on growth and immunmodulation in rohu (L. rohita).     

Effect of stocking density on survival and growth performance of pikeperch, <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.), larvae under controlled conditions

The effect of stocking density on the survival and growth of pikeperch, Sander lucioperca (L.), larvae was examined in two consecutive experiments. In experiment I, 4-day-old larvae [body wet weight (BW): 0.5 mg; total body length (TL): 5.6 mm] were reared in 200-l cylindro-conical tanks in a closed, recirculating system (20 ± 0.5°C) at three stocking densities (25, 50 and 100 larvae l⁻¹) and fed a mixed feed (Artemia nauplii and Lansy A2 artificial feed) for 14 consecutive days. At densities of 25 and 100 larvae l⁻¹, growth rate and survival ranged from 2.7 to 1.9 mg day⁻¹ and from 79.2 to 72.3%, and fish biomass gain ranged from 0.6 to 2.0 g l⁻¹, respectively. There were two periods of increased larval mortality: the first was at beginning of exogenous feeding and the second during swim bladder inflation. In experiment II, 18-day-old larvae (BW: 35 mg; TL: 15.6 mm) obtained from experiment I were reared under culture conditions similar to those of experiment I, but at lower stocking densities (6, 10 and 15 larvae l⁻¹). The fish were fed exclusively with artificial feed (trout starter) for 21 consecutive days. At densities of 6 and 15 larvae l⁻¹, the growth rate and fish biomass gain ranged from 28.8 to 23.1 mg day⁻¹ and from 2.0 to 3.3 g l⁻¹, respectively. The highest survival (56.5%) was achieved at a density of 6 larvae l⁻¹. Mortality at all densities was mainly caused by cannibalism II type behaviour (27–35% of total). In both experiments, growth and survival were negatively correlated and fish biomass gain positively correlated with stocking densities. The present study suggests that the initial stocking density of pikeperch larvae reared in a recirculating system can be 100 individuals l⁻¹ for the 4- to 18-day period post-hatch and 15 individuals l⁻¹ for the post-19-day period.     

The effect of feeding on oxygen consumption and ammonia excretion of juvenile tench Tinca tinca (L.) reared in a water recirculating system

The effect of feeding frequency (one, three, and continuous feeding), feed ration (0.2, 0.5, 0.8% of total fish biomass), and feeding per se on the oxygen consumption (OC, mg O₂ kg⁻¹ h⁻¹) and ammonia excretion (AE, mg TAN kg⁻¹ h⁻¹) of juvenile tench (body weight 15–19 g) and variations in these parameters in daily cycles were examined. Fish metabolism was studied in a recirculating system (rearing tanks of 0.2 m³, water temperature 23 °C). It was found that oxygen consumption and ammonia excretion depended significantly on feed ration. An increase of feed ration from 0.2 to 0.8% of fish biomass caused an increase of OC and AE from 126.80 mg O₂ kg⁻¹ h⁻¹ and 1.95 mg TAN kg⁻¹ h⁻¹ to 187.35 mg O₂ kg⁻¹ h⁻¹ and 8.80 mg TAN kg⁻¹ h⁻¹ (p<0.05). There was no dependence between feeding frequency and the mean rate of oxygen consumption. However, the relationship between feeding frequency and ammonia excretion by juvenile tench was statistically significant (p<0.05). Feeding frequency significantly affected daily fluctuations of AE and OC. It was found that diurnal variations in metabolic rates were strictly related to tench feeding, and the daily variations of AE were significantly higher than OC.     

黑点青鳉的生长和摄食行为发育

针对黑点青鳉实验室养殖成活率低的问题,对其摄食行为发育进行研究,了解其早期阶段的摄食行为发育状况,为人工养殖提供理论依据。通过单摄像机结合镜面成像的方法,对黑点青鳉胚后发育阶段90 d摄食行为的观察与分析,研究了投喂卤虫无节幼体条件下黑点青鳉的生长特征和摄食行为发育。结果显示,幼体体长平均生长率为2.579%/d,体长与日龄间关系为y=3.132+0.383x-0.004x²+0.000 03x³,R²=0.98。通过各项摄食行为指标将其幼体生长发育分为3期6个阶段:仔鱼期(0～10 d)分为前仔鱼期(0～4 d)和后仔鱼期(5～10 d),稚鱼期(11～30 d)分为前稚鱼期(11～18 d)、中稚鱼期(19～24 d)和后稚鱼期(25～30 d),幼鱼期(31～65 d)。黑点青鳉幼体出膜4 d后开始投喂初孵卤虫,至10 d所有鱼苗均能捕食。黑点青鳉仔鱼期幼体死亡率较高,但摄食能力稳步提升,至该期末,摄食成功率提升至45%～55%,摄食效率达0.5～0.6个/min;稚鱼期幼体的各项摄食指标均有大幅度提升,对饵料的响...     

Evaluation of three phytoplankton species as food for the pearl oyster <Emphasis Type="Italic">Pinctada fucata</Emphasis>

In the pearl cultivation farms of the Ehime Prefecture, Japan, mass mortalities of the pearl oyster Pinctada fucata have occurred since 1994. The occurrences of mass mortality roughly coincided with a shift of the dominant phytoplankton from Skeletonema and Chaetoceros to Chaetoceros and Nitzschia all of which belong to Bacillariophyceae. Hence, we evaluated Nitzschia, together with Chaetoceros and Isocrysis, as food for the oyster. Wet weights, lengths, widths, glycogen contents, and growth rates in terms of wet weight of the oysters in all the feeding treatments were significantly higher than those in the non-feeding treatment. The highest glycogen content (2.34%) and growth rate (2.21 g month⁻¹) were found in the Chaetoceros treatment. Growth rate in the Isocrysis treatment (1.63 g month⁻¹) was also high, although glycogen content in this treatment (0.41%) was low. In the Nitzschia treatment, growth rate of the oyster (0.94 g month⁻¹) was the lowest and glycogen content (0.83%) was also low relative to that in the Chaetoceros treatment. Chlorophyll a concentration in fecal pellets was lowest in the Nitzschia treatment (<2.7 μg mg⁻¹), suggesting more complete digestion of Nitzschia by the oyster. Thus, Nitzschia was edible and digestible but not assimilated by P. fucata. We propose the following scenario for the relationship between Nitzschia dominance and mass mortality. When Nitzschia dominates in a culture area, the physiological condition of P. fucata deteriorates due to low assimilation of Nitzschia by the oyster, followed by susceptibility of the oyster to infection by agents lethal to the oyster.     

Cultivation of <Emphasis Type="Italic">Chondrus canaliculatus</Emphasis> (C. Agardh) Greville (Gigartinales,Rhodophyta) in controlled environments

Increased market demand for algal raw materials has stimulated research and development into new cultivation technologies, particularly in countries with economically important seaweed industries. Chondrus canaliculatus is a red alga endemic to the temperate Pacific coast of South America and produces a complex carrageenan. In Chile, this potential marine resource has been underutilized since the early 1990s, after it was replaced mainly by imports of Kappaphycus and Eucheum from Asia. The study of the cultivation of C. canaliculatus in outdoor tanks demonstrates the potential to produce large quantities of algal material due to the high productivity observed. The material produced may be important in Chile as feed for cultured algal herbivores such as Haliotis spp. Data were obtained on the key factors affecting the growth of this alga, including light, temperature, and nutrient concentrations. The results showed that, on a dry weight basis, productivity varied seasonally between 40 g m⁻³ wk⁻¹ in autumn and 200 g m⁻³ wk⁻¹ in spring, and the optimal stocking density in our experiments was 8 kg m⁻³. Effects of self-shading were among the most important limiting factors in the culture. Discussion is presented on the interactions between temperature, pH, salinity, enrichment with N and P, and water exchange on the maximal growth of C. canaliculatus in this culture.     

Immunostimulating influence of herbal biomedicines on nonspecific immunity in Grouper Epinephelus tauvina juvenile against Vibrio harveyi infection

Herbals such as Cynodon dactylon, Piper longum, Phyllanthus niruri, Tridax procumbens, and Zingiber officinalis were extracted with acetone, benzene, butanol, and petroleum ether and screened against the pathogen Vibrio harveyi isolated from the infected Grouper Epinephalus tauvina. Among the different solvent extractions screening to V. harveyi, petroleum ether extracts were suppressed significantly (P < 0.05). Equal proportions of the all-plant extracts were mixed with the artificial feeds at concentrations of 100, 200, 400, and 800 mg kg⁻¹ of diet and fed to grouper juveniles of 20 ± 2 g average weight for a period of 60 days. Every 20 days, fish juveniles were challenged with V. harveyi and the immune response was studied. The herbal diets significantly (P < 0.05) increased the survival, growth, and immune responses compared to the control group. The herbal diets were significantly improved (P < 0.01) in immune parameters such as phagocytic activity and albumin–globulin (A–G) ratio. Among the different concentrations of the herbals in the diet, the 400 mg kg⁻¹ diet was the most effective in the experiment.     

Evaluation of the Ciliated Protozoa,Fabrea salina as a First Food for Larval Red Snapper,Lutjanus campechanus in a Large Scale Rearing Experiment

ABSTRACT

One of the major challenges of culturing of red snapper, Lutjanus campechanus, is providing an appropriate food source at onset of feeding. Ciliates are abundant in marine waters but their significance as a first food for fish larvae is poorly understood as many have no lorica to facilitate their identification in the gut of a larval fish. Fabrea salina is a naked heterotrich ciliate that can be mass cultured at densities up to 84 ± 10 ciliates/mL in 7 days. Its appropriateness as a first food for red snapper larvae was evaluated in a green-water setting using 1-m³ tanks. Larvae were stocked at 10/L, 36 h post-hatch, before first-feeding commenced. Larvae were fed either (1) copepod nauplii, 20–75 μm, only from days 1 to 10; (2) copepod nauplii from days 1 to 10 plus F. salina from days 1 to 5; or, (3) F. salina only from days 1 to 3 plus copepod nauplii from days 4 to 10. Copepod nauplii were added at 2/mL and ciliates were added at 5/mL. Survival after 28 days was 0.28 ± 0.15% for larvae given only copepod nauplii and 2.39 ± 2.75% for those given F. salina and copepod nauplii. Larvae given only F. salina did not survive past 4 days post-stocking. Larvae were more actively feeding in the tanks given F. salina and copepods as first foods with 34.6 ± 8.5% mean daily reduction in copepod nauplii compared to 15.8 ± 16.2% reduction when only nauplii were provided.     

Effect of light intensity and photoperiod on biomass and fatty acid composition of the microalgae, Chlorella vulgaris

The effects of irradiance and photoperiod on the biomass and fatty acid (FA) composition of Chlorella vulgaris were examined in the exponential growth phase. Results indicated significant differences in biomass and FA at different intensities and photoperiods. Maximum biomass (2.05 ± 0.1 g l⁻¹) was at 62.5 μmol photons m⁻² s⁻¹ and 16:8 h light/dark photoperiod. FA composition changed considerably in different light regimes; the maximum percentage of total saturated (SFA) (33.38%) was recorded at 100 μmol photons m⁻² s⁻¹ and 16:8 h photoperiod, while monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids decreased with increasing irradiance and light duration. The maximum percentage of total MUFA (15.93%) and PUFA (27.40%) was recorded at 37.5 μmol photons m⁻² s⁻¹ and 8:16 h photoperiod.     

Effect of prebiotic xylooligosaccharides on growth performances and digestive enzyme activities of allogynogenetic crucian carp (<Emphasis Type="Italic">Carassius auratus gibelio</Emphasis>)

The effect of prebiotic xylooligosaccharides (XOS) on the growth performance and digestive enzyme activities of the allogynogenetic crucian carp, Carassius auratus gibelio, was investigated. XOS was added to fish basal semi-purified diets at three concentrations by dry feed weight: diet 1, 50 mg kg⁻¹; diet 2, 100 mg kg⁻¹; diet 3, 200 mg kg⁻¹, respectively. Twelve aquaria (n = 20) with three replicates for each treatment group (diets 1–3) and control treated without XOS were used. Weights of all collected carp from each aquarium were determined at the initial phase and at the end of the experiment, and the carp survival was also determined by counting the individuals in each aquarium. After 45 days, there were significant differences (P < 0.05) in the relative gain rate (RGR), and daily weight gain (DWG) of diets 1–3 were compared with the control. However, the survival rate was not affected (P > 0.05) by the dietary treatments. For enzymatic analysis, dissection produced a crude mixture of intestine and hepatopancreas of each segment to measure. The protease activity in the intestine and hepatopancreas content of fish in diet 2 (487.37 ± 20.58 U g⁻¹ and 20.52 ± 1.93 U g⁻¹) were significantly different (P < 0.05) from that in the control (428.13 ± 23.26 U g⁻¹ and 12.81 ± 1.52 U g⁻¹) and diet 3 (428.00 ± 23.78 U g⁻¹ and 14.04 ± 1.59 U g⁻¹). Amylase activity in the intestine was significantly higher for diet 2 compared to diet 1 and the control. As for amylase in the hepatopancreas, assays showed higher activity in diet 2 (P < 0.05) compared to the rest.     

Rearing juvenile tench (Tinca tinca L.) under controlled conditions using Artemia nauplii as supplement to a dry diet

A 120-day experiment was performed with 4-month-old juvenile tench [initial mean weight: 0.31 g; total length (TL): 32 mm] to evaluate live Artemia nauplii as supplement to a dry diet for salmonids. All groups received the dry diet. Five treatments, differing in the amount of supplemented Artemia, were tested: without supplement, 450, 900, and 1,800 nauplii g⁻¹ initial fish biomass, and nauplii in excess. Groups that received Artemia supplement had significantly higher survival (between 89.4 and 98.7%) compared to those that received dry diet alone (49.2%), while among them there was no significant difference. Juvenile tench fed the dry diet supplemented with Artemia in excess had a specific growth rate (1.98), weight (3.40 g), and TL (63.90 mm) significantly higher than those in the rest of the treatments. The latter three features were not significantly different under limited co-feeding (450, 900, and 1,800 nauplii g⁻¹ biomass) averaging 1.26 specific growth rate, 1.40 g weight, and 48.50 mm TL. Tench fed the dry diet alone grew significantly less than the rest. Thus, the drawbacks of feeding juvenile tench with dry foods originally formulated for other fish species can be overcome by providing a supplement of Artemia nauplii.     

Decapsulated Artemia cysts as dietary supplement for juvenile crayfish (Pacifastacus leniusculus, Astacidae) at different food supply frequencies from the onset of exogenous feeding under controlled conditions

Considering that the use of decapsulated Artemia cysts as direct food for juvenile crayfish could be an alternative to live nauplii, a 100-day experiment was carried out under controlled conditions to evaluate the effects of cysts, comparing with nauplii, as supplement to a dry diet for salmonids on the survival and growth of juvenile signal crayfish (Pacifastacus leniusculus) from the onset of exogenous feeding (stage 2). The reduction of feeding frequency was also tested. According to a bifactorial design, six treatments, differing in the supplement and feeding frequency, were tested: the dry diet supplemented with Artemia nauplii or decapsulated cysts was supplied once a day, once every two days and once every three days. Survival rates ranged from 56.7% to 81.7%, rising significantly with increasing the feeding frequency. The highest growth (12.94 mm carapace length and 593.08 mg weight) was reached by the crayfish that received the dry diet supplemented with cysts once a day, with significant differences from the rest of the treatments. Considering the supplement, the cysts supported significantly higher growth than the nauplii. Regarding the feeding frequency, growth was higher when the food was supplied once a day, showing significant differences from the other two frequencies (once every two days and once every three days). This study shows that decapsulated cysts are better dietary supplement than live nauplii. In crustacean culture, this is the first report of successful use of Artemia cysts from the onset of exogenous feeding.     

珠江口海域双胞旋沟藻赤潮对卤虫幼体、鱼苗和虾苗的急性毒性

为研究2009年10月下旬在广东珠海海域爆发的双胞旋沟藻赤潮对养殖鱼类及水体中其它生物的影响,实验以卤虫幼体、金鼓鱼苗和凡纳滨对虾苗作为受试生物,在赤潮现场测试双胞旋沟藻对卤虫幼体、鱼苗和虾苗的急性毒性效应。结果显示,24 h双胞旋沟藻对卤虫幼体的LC₅₀(半致死浓度)为9.55×10⁴/mL,藻密度为2.5×10³/mL的双胞旋沟藻对卤虫幼体的LT₅₀(半致死时间)为48.5 h。60 h内该赤潮水体对鱼苗和虾苗的存活无不利影响,卤虫幼体和金鼓鱼苗均可摄食双胞旋沟藻,卤虫幼体对双胞旋沟藻的摄食率低。研究表明,双胞旋沟藻赤潮水体对卤虫幼体有一定的毒性作用,但在低藻密度条件下,卤虫幼体能以该藻为食并维持其生命,双胞旋沟藻对金鼓鱼苗和凡纳滨对虾苗无急性毒性作用。     

Comparative growth of Pacific oyster (Crassostrea gigas) postlarvae with microfeed and microalgal diets

Two trials were carried out in the laboratory in order to assess the effect of microparticulated feed (F) and live (Thalassiosira pseudonana, M) diets on the growth of recently set (396 ± 13 μm shell height) and 2 mm Crassostrea gigas postlarvae. Different proportions of M and F (100:0, 75:25, 50:50; 25:75, 0:100) were delivered in a single dose of 3 h d⁻¹ in trial 1. Dietary M:F proportions of 100:0, 50:50, and 0:100 were delivered as a single pulse of 8 h d⁻¹ (P1) or two pulses of 4 h⁻¹ (P2) in trial 2. Maximal daily M ration was 296 cells μl⁻¹ d⁻¹ (trial 1), 150 M cells μl⁻¹ d⁻¹ (trial 2), or their equivalent F dry weight. Shell height (SH), dry (DW), and organic weight (AFDW) were evaluated weekly. Oysters from trial 1 significantly increased their size after 28 days, and exhibited no significant dietary differences in terms of DW (1.21 ± 0.15 to 2.01 ± 0.28 mg) or AFDW (0.091 ± 0.022 to 0.166 ± 0.029 mg). Newly set postlarvae (trial 2) also exhibited significant growth after 25 days. No dietary differences were observed in trial 2, yet P2 oysters attained significantly higher shell heights (825–912 μm) than P1 oysters (730–766 μm) after 25 d. Pulse effects were marginally not significant in terms of AFDW and growth rate. Together, these findings showed that balanced microfeeds have a practical potential for the culture of early C. gigas postlarvae, when they are delivered in pulse-feeding schemes