Effects of dietary calcium and phosphorus supplementation on the growth performance of juvenile spotted babylon <Emphasis Type="Italic">Babylonia areolata</Emphasis> culture in a recirculating culture system

A feeding experiment was conducted to determine the effects of dietary calcium and phosphorus, and the interaction between calcium and phosphorus, on the growth of juvenile spotted babylon, Babylonia areolata, cultured in a recirculating culture system. Nine isonitrogenous experimental diets supplemented with three levels of calcium (1, 4, and 7%) for each of three levels of phosphorus (1, 3, and 5%) were prepared using fish meal, squid meal, and shrimp meal as the main protein sources. Juveniles with an initial average body weight of 0.59 ± 0.09 g were fed to satiation once daily with one of the nine diets for 180 days. Absolute and specific growth rates were calculated for both shell length and whole wet body weight. Results showed that dietary calcium and phosphorus supplementation significantly affected the growth of juvenile spotted babylon (P < 0.05), but not survival and feed-conversion ratio. The specific growth rate in shell length (SGRL) ranged from 0.32 to 0.39% day⁻¹. No significant difference among phosphorus levels and no significant interaction between calcium and phosphorus in SGRL of the spotted babylon (P > 0.05) was found, but significant differences were observed among calcium levels, irrespective of phosphorus levels (P < 0.05). For 1 and 7% supplemental calcium, the spotted babylon had significantly higher SGRL than those fed diets supplemented with 4% calcium. However, the specific growth rate in body weight (SGRW) ranged from 0.91 to 1.19% day⁻¹ with no significant difference among calcium and phosphorus levels and no significant interaction between calcium and phosphorus (P > 0.05). Survival and feed-conversion ratio were not significantly affected by dietary calcium and phosphorus levels with ranges from 91.00 to 95.00% and 2.43 to 2.76, respectively. At the end of the experiment, shell abnormality of B. areolata was found for all feeding trials.     

Effect of body size and sub-optimal water quality on some hemato-immunological parameters of spotted babylon snail <Emphasis Type="Italic">Babylonia areolata</Emphasis>

Cellular and humoral effectors are imperative for the innate defense mechanisms of invertebrates, including the spotted babylon snail Babylonia areolata, a marine gastropod belonging to the family Buccinidae. In this study, we have investigated the influence of body size [5–8 g (small), 10–12 g (medium) and 15–17 g (large)], and culture waters of varied quality [natural seawater, low salinity, low alkalinity, high total ammonia nitrogen (TAN) and artificial seawater] on some hemato-immunological parameters [total hemocytic counts (THC), hemolymphatic glucose, total protein concentration, phenoloxidase (PO), agglutinating and lysozyme activity] of the snail. Growth performance measures and survival of test snails were also evaluated after rearing them in culture water of varied quality. Body size did not influence most parameters assessed, except that the lysozyme and PO activities of medium and large-size snails were higher than those of the small-size snails. Sub-optimal culture water quality affected hemato-immunological factors, growth and/or survival of the spotted babylon snail. Seawater with low salinity, low alkalinity and a high TAN level caused decreased THC, hemolymphatic glucose, and PO activity; increased lysozyme activity; and clearly retarded growth of the snail. The snails held in artificial seawater could not survive after 4 weeks, suggesting the lack of certain essential factors necessary for their survival.     

Growout of hatchery-reared juvenile spotted babylon (<Emphasis Type="Italic">Babylonia areolate</Emphasis> link 1807) to marketable size at four stocking densities in flow-through and recirculating seawater systems

Hatchery reared juvenile spotted babylon, Babylonia areolata, were raised in canvas rearing tanks at four stocking densities (100, 200, 300 and 400 ind. m^–2) in flow-through and recirculating seawater systems until they reached the marketable sizes of 100–140 snails/kg. At all stocking densities, final increments in mean length and weight of snails held in flow-through systems were higher than those in recirculating systems, there was a significant effect (p < 0.05) of culture system on final length and weight. Mean (±SE) survival of snails held at 100 ind. m^–2 in the flow-through system was 100.0 ± 0.1% but was not significantly higher than survival in any other treatment (p > 0.05). Mean survival of snails held in the recirculating system was not significantly lower than at any stocking density in the flow-through system (p > 0.05).     

Growth,food efficiency,and biochemical composition of juvenile spotted babylon <Emphasis Type="Italic">Babylonia areolata</Emphasis> (Link) fed on conventional trash fish and a formulated moist diet

A 120-day feeding trial was conducted to determine growth, feeding efficiency, and biochemical composition of juvenile spotted babylon Babylonia areolata (initial mean weight of 1.48 ± 0.06 g) fed on conventional trash fish and a formulated moist diet in a flow-through grow-out system. The snails readily accepted the formulated moist diet and showed good growth and survival during the trial. There were no significant differences in specific growth rate, feeding efficiency, and survival between the snails fed on trash fish or the formulated moist diet. At the end of the experiment, biochemical analysis of the snail flesh showed significant differences in flesh quality, with the snails fed on trash fish having a significantly higher crude protein compared to those fed on the formulated diet, but there was little difference in crude lipid content. Whole body tissue of snails fed on trash fish had significantly higher total amino acid, essential amino acid, and non-essential amino acid levels compared to those fed the formulated diet. This study showed that the formulated moist diet can be readily used for B. areolata growout for maximizing growth, survival, and feeding efficiency; however, further research is needed to improve the flesh quality particularly amino acid and fatty acid levels before its suitability for B. areolata is assured.     

Effect of dietary supplementation of brewers yeast and nucleotide singularly on growth,survival and vibriosis resistance on juveniles of the gastropod spotted babylon (<Emphasis Type="Italic">Babylonia areolata</Emphasis>)

This study was undertaken to evaluate the use of brewers yeast and nucleotides as a growth promoter and to provide vibriosis resistance for the juveniles of gastropod spotted babylon (Babylonia areolata). Juvenile spotted babylon (0.3 g initial weight) were randomly distributed at a density of 50 snails in 45-L aquaria and fed a basic diet (40% crude protein) containing two incremental levels of 1 and 2% brewers yeast and nucleotides singularly for 4 months. After the feeding trial, snails from each treatment were challenged by pathogenic bacteria Vibrio alginolyticus given by intramuscular injection and kept under observation for 5 days to record clinical signs and daily mortality rates. Results indicated that the snails fed with diets supplemented with brewers yeast or nucleotides exhibited significantly greater growth than those fed the basic diet (P < 0.05) and significantly better food conversion ratios compared to snails fed the basic diet (P < 0.05). These results indicated that dietary supplementation of brewers yeast or nucleotides, at least at the tested dosages, enhanced spotted babylon growth. Supplementing the diet with 1% brewers yeast promises to provide appropriate resistance to V. alginolyticus.     

Differences in fatty acid composition of egg capsules from broodstock spotted babylon, <Emphasis Type="Italic">Babylonia areolata</Emphasis>, fed a local trash fish and formulated diet under hatchery conditions

This study is the first attempt to condition broodstock Babylonia areolata using formulated diets under hatchery conditions. Samples of spotted babylon egg capsules from broodstock fed either a formulated diet or a local trash fish, carangid fish (Seleroides leptolepis) for 120 days were analyzed for proximate composition and fatty acid composition. The formulated diet contained significantly higher levels of arachidonic acid (20:4n − 6; ARA), eicosapentaenoic acid (20:5n − 3; EPA) and docosahexaenoic acid (22:6n − 3; DHA) than those of the local trash fish. The formulated diet also had significantly higher ratios of DHA/EPA and (n − 3)/(n − 6) PUFA than those of local trash fish but not for the ARA/EPA ratio. The compositions of egg capsules produced from broodstock fed formulated diet contained significantly more ARA, EPA and DHA compared to broodstock fed the local trash fish. The ARA/EPA and DHA/EPA ratios in egg capsules were significantly higher in the trash fish—fed group compared to those fed the formulated diet. However, (n − 3)/(n − 6) PUFA ratios in egg capsules produced from broodstock fed the formulated diet did not differ significantly compared to those from broodstock fed the local trash fish. The relatively low DHA/EPA, ARA/EPA and (n − 3)/(n − 6) ratios in the egg capsules produced from the formulated diet—fed broodstock B. areolata suggested that this diet is inferior, when compared to the traditional food of trash fish.     

Effects of dietary lipid levels on growth performance,feed utilization and fatty acid composition of juvenile Japanese seabass (<Emphasis Type="Italic">Lateolabrax japonicus</Emphasis>) reared in seawater

Triplicate groups of 40 Japanese seabass Lateolabrax japonicus (initial weight, 11.3 ± 0.4 g) reared in seawater (salinity, 30.0–33.0 g L⁻¹) were fed with five isonitrogenous (41.3 ± 0.2% crude protein) and isoenergetic (18.5 ± 0.3 MJ kg⁻¹) experimental diets formulated with increasing lipid levels (4.3, 8.4, 12.2, 15.8 and 20.1% lipid) for 10 weeks. Survival throughout the feeding experiment ranged from 87.5 to 100%, but the survival of fingerlings fed with the 4.3% lipid diet was significantly lower than the rest of the diets. At the end of the feeding experiment, fish fed with 12.2% lipid diet showed optimal growth performance (P < 0.05). Lipid contents of whole body, liver and muscle increased in parallel with the increase in dietary lipid levels. Viscerosomatic index (VSI), hepatosomatic index (HSI) and muscle lipid content were higher in 20.1% lipid group than those in the rest of the lipid level groups indicating that viscera and muscle tissues played important contributions to body lipid deposition. High proportions of 18:1n-9, eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), and low concentrations of n-6 polyunsaturated fatty acids (PUFAs) occurring in liver and muscle, to some extent, reflected fatty acid (FAs) composition in the experimental diets.     

Effects of dietary protein levels on growth performance and body composition of juvenile parrot fish, <Emphasis Type="Italic">Oplegnathus fasciatus</Emphasis>

The present study was conducted to evaluate the effects of dietary protein levels on growth, biometrics, hematology and body composition in juvenile parrot fish Oplegnathus fasciatus. Fish averaging 7.1 ± 0.06 g (mean ± SD) was randomly distributed into 15 net cages (each size: 60 × 40 × 90 cm, W × L × H) as groups of 20 fish. Five isocaloric diets (16.7 kJ/g energy) were formulated to contain crude protein levels (CP) as 35 (CP₃₅), 40 (CP₄₀), 45 (CP₄₅), 50 (CP₅₀) and 60 % (CP₆₀) in the diets. Fish were fed one of the experimental diets at apparent satiation twice a day in triplicate groups. At the end of 8-week feeding trial, weight gain (WG) of fish fed with CP₅₀ and CP₆₀ diets were significantly higher than those of fish fed with CP₃₅, CP₄₀ and CP₄₅ diets. Fish fed with CP₄₅, CP₅₀ and CP₆₀ diets had higher feed efficiency (FE) and specific growth rate (SGR) than those of fish fed with CP₃₅ and CP₄₀ diets. Protein retention efficiency (PRE) decreased with increase of dietary protein levels among fish fed with the experimental diets. Whole-body crude protein and lipid contents increased with the dietary protein level up to CP₅₀ diet. In conclusion, analysis of variance (ANOVA) revealed that the optimum dietary protein level could be 50 % for maximum growth of juvenile parrot fish, while the broken-line analysis of WG suggested that the level could be 48.5 %, in a diet containing 16.7 kJ/g energy.     

Effects of two dietary protein levels on energy balance and digestive capacity of <Emphasis Type="Italic">Octopus maya</Emphasis>

Octopus maya is a carnivorous species and protein is the main energy source. During the present study, two different dietary protein levels (40 and 60% CP) were offered to octopuses as specifically designed artificial diets, to determine protein needs and the effects on metabolism. Frozen crab (Callinectes spp.) was used as control. Results obtained demonstrated that crab remains as one of the best diets for O. maya. The artificial diet with 60% CP produced a low but positive growth rate, and at times, a physiological response similar to that observed in octopuses fed crabs. The present results show the capacity of O. maya juveniles to adjust their digestive enzymes to different types of food and protein level, and this appears to be well correlated with octopus growth. General proteases and trypsin from the pancreas were well correlated with growth rates. A low activity was observed in octopuses fed 40% PC diet (negative growth rate), while a high activity was present in octopuses fed 60% CP diet and crabs (low and high growth rate, respectively). In contrast, these same enzymes were inducted in the salivary glands of octopuses fed with the diet that promoted weight loss (40% CP diet), while a reduced activity was observed in octopuses fed crabs. Energy budget indicates that the animals ingested more than 1,000 kJ week⁻¹ kg⁻¹; with such energy, octopuses should satisfy their physiological demands such as was observed when animals were fed crab (I = 1,300 kJ week⁻¹ kg⁻¹; P = 834 kJ week⁻¹ kg⁻¹). However, a very low digested energy was observed in octopuses the fed artificial diets, indicating that these could have a factor that limits digestibility.     

Modulation of appetite,lipid and glucose metabolism of juvenile grass carp (<Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis>) by different dietary protein levels

This study was undertaken to explore the systemic metabolic strategies of juvenile grass carp (Ctenopharyngodon idellus) to maintain growth when fed with different dietary protein levels. The optimal growth group and two growing discomfort groups were selected through the basic data, to explain the growth difference from appetite regulation and lipid and glucose metabolism perspective. Three experimental diets were formulated with three dietary protein levels at 200.3, 296.1 and 442.9 g kg^?1, named P1, P2 and P3, respectively. Juvenile grass carp (initial body weight 12.28 ± 0.14 g) were fed with three diets with 3 replications per dietary treatment in an indoor recirculation system for an 8-week feeding trial. Fish fed with diet P2 dietary group showed significantly higher WG, SGR, FI and PER than other groups. Compared with other groups, mRNA expressions of NPY, Y8a and Y8b in fish fed with P2 significantly down-regulated, while the expressions of CCK and CART in fish fed with P3 significantly down-regulated (P < 0.05). With increasing dietary protein levels, G6Pase, GK, PK and PEPCK were all significantly inhibited (P < 0.05). For lipid metabolism, the mRNA expression of ACC in P1 dietary group was significantly higher than P3 dietary group; besides, LPL expression in P3 group was significantly higher than other two groups (P < 0.05). PPARα expression in P2 was significantly lower than other groups (P < 0.05). These results suggested that grass carp fed with P2 (296.1 g kg^?1 protein level) showed highest weight gain, contributed to more balanced nutrient metabolism and appetite regulation. Too high dietary protein (442.9 g kg^?1) should be avoided because it induced lowest PER, body lipid and liver lipid, and inhibited glucose and lipid metabolism in juvenile grass carp.     

Wheat grains fermented by fungal mycelia (<Emphasis Type="Italic">Pleurotus ostreatus</Emphasis> or <Emphasis Type="Italic">Lentinus edodes</Emphasis>) as alternative feed ingredients for juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

We investigated the effects of replacing non-fermented wheat grains with wheat grains fermented by fungal mycelia in the diet of juvenile rainbow trout (Oncorhynchus mykiss). We assessed growth performance, feeding parameters, and body composition in three experimental groups (0.33?±?0.01 g, in triplicates of 50 individuals each). The diets for all the groups contained ca. 43% protein and 19% lipids. Experimental diets were made by replacing the 100 g kg^?1 of wheat grains present in the basal diet (CTRL) with the same proportion of wheat grains fermented by Pleurotus ostreatus (PWD) or Lentinus edodes (LWD) mycelium. Fish were fed to apparent satiation twice a day for 56 days. Both, PWD and LWD, significantly increased fish body weight from day 28 onwards. Final body weight was 2.37?±?0.04 g (CTRL), 4.29?±?0.02 g (PWD), and 3.50?±?0.05 g (LWD), and feeding efficiency (%) was increased from 64.5?±?0.7 (CTRL) to 92.5?±?0.5 (PWD) and 84.8?±?1.5 (LWD). The experimental diets also improved nutrient retention efficiency (%): 30.0?±?0.5 (PWD), 27.7?±?1.1 (LWD), and 21.0?±?0.1 (CTRL), for crude protein; 40.3?±?0.6 (PWD), 31.0?±?1.8 (LWD), and 16.1?±?0.7 (CTRL), for ether extract; and 16.1?±?0.1 (PWD), 14.0?±?0.3 (LWD), and 11.6?±?0.6 (CTRL), for phosphorus. Body lipid content was highest for PWD followed by LWD and CTRL (81.4?±?1.4, 63.2?±?2.5, 42.3?±?2.6 g kg^?1, respectively), while viscerosomatic index was lowest for PWD (p?<?0.05). Liver glycogen in LWD and PWD fish (0.62?±?0.10 and 0.21?±?0.08% liver weight) was significantly higher than in CTRL fish (0.05?±?0.01% liver weight). Wheat-mycelium meals appear to be suitable dietary ingredients for improving juvenile rainbow trout growth and nutritional performance. These benefits vary according to the mushroom species used.     

Effects of potential probiotic <Emphasis Type="Italic">Lactococcus lactis</Emphasis> subsp. <Emphasis Type="Italic">lactis</Emphasis> on digestive enzymatic activities of live feed <Emphasis Type="Italic">Artemia franciscana</Emphasis>

In the present study, cellulase, protease, lipase and amylase activities were performed to investigate the effects of Lactococcus lactis subsp. lactis CF4MRS bioencapsulation of Artemia franciscana. Our results show that cellulase activities (total cellulase—FPase activity, exoglucanase and endoglucanase—CMCase activity) were significantly higher (P < 0.05) in A. franciscana tissue homogenates compared to those in the control group after 8 h of L. lactic bioencapsulation. Notably, an exception case was found in β-D-glucosidase activity, whereby the cellulase activity was not significantly different (P > 0.05) compared to the control group. Administrations of L. lactis at cell concentration of 10⁸ CFU mL^?1 showed considerable improvement of other important enzymatic activities such as amylase, protease and lipase in A. franciscana. The amylase/protease ratio in probiotic-treated A. franciscana was recorded at 0.343, approximately two times higher than those without probiotic administration (0.184). In contrary, amylase/lipase ratio showed half of a reduction (0.330) in L. lactis-administrated A. franciscana compared to the control (0.614). Our study suggests that important digestive enzymes, e.g., cellulase, amylase, protease and lipase, can be enhanced through bioencapsulation of A. franciscana with L. lactis subsp. lactis, which could in turn lead to further stimulation of endogenous enzymes in the fish and shrimp larvae.     

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.     

Effects of dietary protein levels on growth,feed utilization,protein retention efficiency and body composition of young <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> (Bloch)

An 8-week growth trial was conducted to assess the effect of dietary protein on growth, feed utilization, protein retention efficiency, and body composition of young Heteropneustes fossilis (10.02 ± 0.09 g; 9.93 ± 0.07 cm). Isocaloric (4.15 kcal g⁻¹, GE) diets with varying levels of protein (25, 30, 35, 40, 45, and 50% of the diet) were fed near to satiation to triplicate groups of fish. Optimum dietary protein was determined by analyzing live weight gain (LWG%), feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR%), and protein retention efficiency (PRE%) data. Maximum LWG% (167), best FCR (1.42), PER (1.75), SGR (1.76), and PRE (31.7%) were evident in fish fed 40% protein diet (Diet 4). Body protein data also supported the above level. However, second-degree polynomial regression analysis of the above data indicated that inclusion of dietary protein in the range of 40–43% is optimum for the growth of young H. fossilis.     

Influence of the dietary inclusion of <Emphasis Type="Italic">Gracilaria cornea</Emphasis> and <Emphasis Type="Italic">Ulva rigida</Emphasis> on the biodiversity of the intestinal microbiota of <Emphasis Type="Italic">Sparus aurata</Emphasis> juveniles

Partial substitutions of fish meal by 5, 15, or 25 % of Gracilaria cornea or Ulva rigida in experimental diets were evaluated to study their effects on biodiversity of intestinal microbiota composition in gilthead seabream (Sparus aurata) juveniles. The diets were offered to duplicate groups of 15 juvenile fish (14.0 ± 0.5 g) for 70 days, and at the end of the experiment the intestinal microbiota from four specimens of each treatment was analysed by denaturing gel gradient electrophoresis. Results showed that the substitution of fish meal by algae meal induced important modifications in the intestinal microbiota community, as a big reduction of the biodiversity when the highest percentage (25 %) of U. rigida was included. On the contrary, an increase on the number of species was detected when a 15 % of algae was included. Various Lactobacillus delbrueckii subspecies were selectively stimulated when G. cornea was included in the feed, and other bacterial species, such as those included in the Vibrio genus, were reduced.     

Dietary value of gametophytes and juvenile sporophytes of the brown macroalga <Emphasis Type="Italic">Eisenia bicyclis</Emphasis> for juvenile abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis>

The dietary value of juvenile stages (gametophyte and juvenile sporophyte) of the brown macroalga Eisenia bicyclis for post-larval and juvenile abalone Haliotis diversicolor of 2.0–6.5 mm in shell length (SL) was examined and compared with that of a benthic diatom, Nitzschia sp., in laboratory experiments. Most abalone actively fed on these diets, but there were large variations in the growth rate among the diets and among the growth stages of abalone. Growth rates of abalone fed on Nitzschia sp. were highly variable within each growth stage, but showed no clear differences among growth stages. In contrast, in abalone fed gametophytes or juvenile sporophytes, growth rates linearly increased as abalone grew. Growth rates of >60 μm SL/day were observed in juveniles of >3 mm SL fed gametophytes, and juveniles of >5 mm SL fed juvenile sporophytes. These results indicate that the dietary value of the juvenile stages of E. bicyclis for the abalone changes as they grow, and with growth juvenile abalone begin to efficiently utilize gametophytes and juvenile sporophytes in that order.     

Growth and feed utilization of gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>, L.) fed to satiation and restrictively at increasing dietary energy levels

Three isoproteic (47% protein) diets were formulated to contain graded levels of crude fat (diet D16:16%, diet D24: 24% and diet D32: 32%). Each diet was fed to satiation in three and to 80% satiation in two replicate groups of gilthead sea bream (Sparus aurata), having an initial body weight of 72–74 g. The trial lasted 81 days. Groups fed to satiation showed higher final body weight (FBW; 238.8–252.3 g vs. 218.0–229.3 g) and daily growth index (DGI; 2.49–2.65%/day vs. 2.27–2.34%/day) than those fed to 80% satiation. Feed intake was significantly different both for feeding level and for diet composition. Fish fed to satiation had higher feed conversion rate (FCR) compared to the 80% satiation groups (1.33–1.44 vs. 1.13–1.17; P ≤ 0.001). Within satiation groups, FCR was significantly lower in fish fed D16 compared to fish fed D32 (1.33 vs. 1.44, P ≤ 0.05), whereas no statistical differences were found within the 80% satiation groups. The increase in dietary lipid level did not improve growth performance, feed efficiency and protein utilization but decreased gross lipid efficiency. Conversely, a reduction in ration from satiation to 80% satiation decreased DGI, thus improving FCR. Feed costs were influenced by dietary energy level and feeding ratio, the lowest energy diet at 80% satiation being the most profitable combination among the variables.     

Low-salinity tolerance of juvenile fugu <Emphasis Type="Italic">Takifugu rubripes</Emphasis>

ABSTRACT:   To study the adaptability of juvenile fugu Takifugu rubripes to low-salinity environments, fish were transferred from full-strength seawater (100% SW) to freshwater (FW) and 25, 50, 75 and 100% SW, and checked for mortality over 3 days. No mortality was observed in 25–100% SW, whereas all fish died in FW. In fish transferred to 25–100% SW, blood osmolality was maintained within a physiological range. To further explore the lower limit of salinity that fugu could tolerate, fish were transferred from 100% SW to FW and 1, 5, 10, 15 and 25% SW. All fish survived in 5–25% SW, but fish died in FW and 1% SW. In fish surviving transfer to FW and 1 and 5% SW, blood osmolality was decreased to a near sublethal level of approximately 300 mOsm/kg·H₂O. Therefore, the lower limit of salinity tolerance is estimated to lie between 5 and 10% SW. Preacclimation in 25% SW for 7 days did not essentially affect the survival salinity range. Although survival rates and blood osmolality were slightly improved by preacclimation in 25% SW, blood osmolality was markedly decreased in salinities less than 10% SW, as was seen in the direct transfer. Neither chloride cell morphology nor sodium-potassium adenosinetriphosphatase activity in the gills showed a significant change following transfer to low salinities. These findings indicate that fugu can be adapted to hypoosmotic environments to some extent, exerting hyperosmoregulatory ability, although chloride cells are less likely to absorb ions in hypoosmotic environments.