Estimation of kelp forest, <Emphasis Type="Italic">Laminaria</Emphasis> spp., distributions in coastal waters of the Shiretoko Peninsula,Hokkaido, Japan,using echosounder and geostatistical analysis

Sustainable management of the kelp forests of the Shiretoko Peninsula, a World Natural Heritage site, is necessary due to kelp’s ecological and economic importance. The objectives of this study were to estimate the area of kelp forests and to clarify their spatial characteristics in coastal waters of the Shiretoko Peninsula. Data on the presence/absence and thickness of kelp forests were collected via acoustic observation on transects over about 80 km using an echosounder at 200 kHz. Acoustic data were geostatistically interpolated, and the areas covered by kelp forests were estimated. Differences in kelp distribution between the eastern and western sides of the peninsula were compared. The total area of kelp forest was 3.88 km² (eastern area: 3.49 km²; western area: 0.39 km²). The range of thickness of the kelp forests was 34–91 cm. Many kelp forests in the eastern area were thick (>78 cm) and distributed continuously, while kelp forests in the western area were sparsely distributed.     

Impact of shellfish biodeposits and rotten seaweed on the sediments of Ailian Bay,China

We assessed the function of a Patinopecten yessoensis and Saccharina japonica integrated multi-trophic aquaculture (IMTA) model on the level of organic matter produced in the environment. The study was conducted in March–July 2012 using stable carbon and nitrogen isotope methods. Results showed that the quantity of rotten kelp increased considerably over these 5 months, with the length of the rotten blades reaching 150 cm in July. The contribution rates of biodeposits by the shellfish and kelp to the suspended particulate matter (SPM) were 3.93 ± 0.39 and 4.99 ± 1.09 %, respectively, but contribution rates to the sediments in the IMTA area were very low. In May and July, rotting kelp contributed 1.06 ± 0.46 and 1.64 ± 0.13 % in the kelp area, respectively. The organic carbon and nitrogen content of sediments from the IMTA area was significantly higher than from the kelp area (P < 0.05). C% and N% in SPM from the IMTA area were four times those from the kelp area (P < 0.05), but the C and N content in sediments were still at a low level.     

Phenology of the kelp <Emphasis Type="Italic">Saccharina japonica</Emphasis> and its effect on the gonad index of the sea urchin <Emphasis Type="Italic">Mesocentrotus nudus</Emphasis> across a depth gradient off the Sanriku coast,northeastern Japan

The kelp Saccharina japonica is a dominant seaweed along the Sanriku coast where fisheries for sea urchin and abalone are among the most prosperous in Japan. We investigated the phenology of the kelp at depths of 6, 9 and 12 m from March 2015 to March 2016. The sea urchin Mesocentrotus nudus, a dominant herbivore off the coast, was also monitored with respect to its gonads for fishery use. Juvenile kelp appeared in March and rapidly elongated until May. Weight of the kelp significantly increased from April to July. Sori formation commenced from September and ceased in December. Density and biomass of the kelp were higher in the shallower sites than in the deeper one throughout the year. The highest biomasses recorded between July and October were 3773, 1939 and 501 g dry weight m^?2 at depths of 6, 9 and 12 m, respectively. No regrowth of kelp blades was observed, indicating that S. japonica in this region has an annual life cycle. The gonad index of the sea urchin in the 12-m site was lower than that in the 6- and 9-m sites, indicating the close relation of the gonad index with the biomass of the kelp.     

Effects of biofilms as the main and as a supplementary food on the survival,somatic growth and gonad enhancement of sea urchin Strongylocentrotus intermedius

Cultured sea urchins of similar size (mean ± SE = 4.33 ± 0.48 g in body weight) were fed biofilms only, kelp (Laminaria japonica)+biofilms (biofilms as supplementary food) and a control diet of kelp only for 7 months in the laboratory. The somatic growth and the survival rate of the sea urchins were measured monthly, and the gonad wet weight and gonad color difference were determined at the end of the experiment. The results show that diet did not significantly affect survival rate (P > 0.05), but had highly significant effects on somatic growth from the first month to the end of the experiment (P < 0.01). Sea urchins fed biofilms only showed negligible or even negative somatic growth at the end of the experiment. Sea urchins on the kelp+biofilms grazed biofilms and consumed kelp during the experiment, and showed sustained greater increase in body weight than those of fed kelp only after the fourth month (P < 0.05). The biofilms may have supplied micronutrients. At the end of the experiment, gonad production of sea urchins fed biofilms was too little (0.11 ± 0.09 g) to identify sex and measure color. Gonad wet weights of males and females and gonad color fed kelp+biofilms did not differ significantly from those of fed kelp only (P > 0.05). However, sea urchins fed kelp+biofilms were more uniform in gonad color than those fed kelp only (P < 0.01), indicating biofilms supplementation could reduce the percentage of low-grade roe. This study therefore reveals the potential of biofilms as a supplementary food in the culture of sea urchins.     

Recruitment and movement of the hard clam Meretrix lusoria in a tidal river of northern Kyushu,Japan

Size-frequency distributions of Meretrix lusoria, a commercially important bivalve in Japan, were compared among 6 sites in tidal flats of a small river in Kafuri Bay, northern Kyushu, Japan during 2006–2008. In Kafuri Bay, the hard clam resource is strictly managed and mean biomass of this species on the fishing ground (about 1.5 km²) exceeded 1.5 kg m^?2 in 2008. Small clams (<5 mm in shell length, SL) were most abundant in the border area between the river and the sea, while large clams (>40 mm SL) were rare there. In contrast, in the lower site of the marine area (site L), most clams were >30 mm SL. These results indicate that small clams move from riverine to marine areas with growth (post-settlement movement). Year-round, very small clams (<1 mm SL) were present and clams that were 2–5 mm SL were very rare, although the spawning season is thought to occur in summer. Probably, the early growth of many new recruits is very slow and most may even be <1 mm SL in the next spring, although some clams grow to >5 mm SL in a short period of time.     

南日岛养殖海带的生长、碳氮磷元素含量及对海水颗粒和溶解有机物的影响

为了研究养殖海带的生态环境效应,通过南日岛海带养殖区现场测量和取样,分析了海带的生长速率,组织C、N、P含量和元素比值,以及养殖区颗粒和溶解有机物的季节变化。结果显示,在1个生长周期内,海带的湿重与长度呈明显幂函数关系(W=0.02 L7.57,R2=0.84),海带的湿重、长度和宽度与养殖天数具有明显的线性相关关系(湿重、长度和宽度与养殖天数的R2分别为0.96、0.96和0.93)。海带C/N比变化范围为9.13～18.66,N/P比变化范围为11.32～18.48,C/P比变化范围为153.18～267.99。海带C/P比与P含量呈明显指数函数关系(Y=748.30 e-4.10X,R2=0.88),C/N比与N含量呈明显指数函数关系(Y=50.21 e-0.60X,R2=0.92)。海带养殖海区POC、PON和POP的变化范围分别为0.33～0.86、 0.07～0.11和0.01～0.02 mg/L; DOC、 DON和DOP含量的变化范围分别为1.98～17.06、0.20～0.55和0.01～0.04 mg/L。海带C、N、P含量的变化范围分别为22.82%～26.43%、 1.65%～2.97%和0.25%～0.42%。收获时海带的平均碳、氮、磷含量分别为26.17%、1.76%和0.29%,以2018年福建海带养殖总产量76.83万t计算,即通过收获分别可移除C、N、P 20.13、1.35和0.22万t。研究表明,养殖海带可能是养殖区海水有机物的重要来源,是近海碳循环的重要组成之一。     

Spatial movement of black sea bream <Emphasis Type="Italic">Acanthopagrus schlegelii</Emphasis> around the oyster farming area in Hiroshima Bay,Japan

In order to obtain information for preventing oyster spats predation, we investigated the horizontal and vertical movement patterns of black sea bream Acanthopagrus schlegelii inhabiting an oyster farming area in Hiroshima Bay by active tracking. Seven adult fish equipped with depth transmitters were tracked for 65 days around the oyster farming area. Six of the seven fish were found in the oyster rafts for a cumulative duration of 55 days. The daily movement distance and minimum convex polygon home range of these fish were 0.13–0.78 km/day and 0.11–1.14 km², respectively. The swimming depth of these fish were mainly between 1 and 15 m, which coincided with the depths of the submerged oyster wires. Our observations suggest that black sea bream inhabiting the oyster farming area in Hiroshima Bay are highly dependent on the spatial arrangement of the oyster rafts.     

Comparing the stability of successional transient models in kelp forests and barrens (south-east Pacific): Implications for conservation monitoring

1. Ecological stability based on statistical variability was contrasted with the asymptotical local stability of transient states during successional changes in community structure in kelp forests and barren grounds.
2. Simplified semi-quantitative ecological models with different levels of complexity were constructed to represent transient successional states in kelp and barrens, and Routh–Hurwitz's criteria and Levins' criterion of local stability were also estimated.
3. The results suggest that ecological stability based on statistical variation does not match local (mathematical) stability, since although successional changes in kelp exhibited less variability (measured as percentage coefficient of variation), barren beds were more locally stable. The local stability criteria used in the current work could be a suitable technique for evaluating the likelihood of transient ecological states to resist or change, since it considers states at equilibrium to maintain their properties only against small disturbances.
4. These outcomes are relevant because the natural alternation between kelp and barrens could be disrupted by the intensive harvest of kelp species carried out over the last 10 years on the central-north Chilean coast and in other temperate ecosystems.
5. Additionally, the negative effects of harvesting kelp species could have a synergetic relationship with other drivers such as climate change and coastal pollution. Thus, strict policy managements to limit the kelp harvest are deeply encouraged. A monitoring programme for assessing the current conditions of benthic–pelagic ecosystems along the Chilean coast is also required.

     

Heavy infection of Ichthyophthirius multifiliis in striped catfish (Pangasianodon hypophthalmus,Sauvage 1878) and its treatment trial by different therapeutic agents in a control environment

ABSTRACT

Striped catfish (Pangasianodon hypophthalmus) fingerlings were stocked (60 fishes/m³) in cemented square tanks for ornamental fishery purposes at the College Fish Farm in Mangalore. A total of 400 fishes with a mean weight (g) ranging from 3.24 ± 1.21 to 6.70 ± 1.13 and a mean length (cm) of 7.50 ± 0.94 to 9.50 ± 1.10 were examined. A severe outbreak of salt-like granule white spots was found on the body surface. Ichthyophthirius multifiliis, a ciliate pathogen, was identified as the causative agent by clinical signs, wet mount, and histopathological observations. Infected fishes were transferred and equally distributed to the 0.45 m³ glass aquaria and treated with three treatments: (T1) methylene blue + salt; (T2) raising temperature with salt; and (T3) formalin + malachite green. The best fingerling survival (55 ± 9.36%) was obtained by elevated water temperature with salt in T2.     

Prebiotic,probiotic, and synbiotic in the diet of Nile tilapia post-larvae during the sex reversal phase

This study evaluated the use of the prebiotic Active-MOS® (mannanoligosaccharides—Biorigin®) and two probiotics: PAS-TR® (Bacillus subtilis and Bacillus cereus var. toyoi—Imeve®) and Bioplus 2BC® (1.6 × 10¹⁰ UFC g^?1 de Bacillus subtilis and 1.6 × 10¹⁰ UFC g^?1 Bacillus licheniformis—Christian Hansen®) tested separately and together, in the diet of Nile tilapia post-larvae during the sex reversal phase. The experiment was conducted in two stages: (i) a total of 2160 3-day-old post-larvae (PL) (10.39 ± 0.85 mm and 12.28 ± 3.15 mg) were used and distributed in 24 tanks of 40 L each (3.0 PL L^?1). Growth performance, chemical analysis of carcass, bacterial recovery, and histomorphometry of intestinal villi were evaluated; (ii) 240 tilapia (4.28 ± 0.19 cm and 1.19 ± 0.09 g) from the previous experiment were used and stocked at 10 PL per aquarium. The parameters evaluated were survival and relative protection level after bacterial challenge against Aeromonas hydrophila. Six treatments with four replications in a completely randomized design were used for both experimental stages. Additives in the diet of tilapia post-larvae did not determine significant differences in growth, survival, microbiological, or histomorphometric parameters in this study. Nevertheless, after the experimental infection, advantages on the use of the additives were observed in terms of higher relative protection levels (38.10%) and relative percent survival in fish receiving Active-MOS® + Bioplus 2BC®. Therefore, we recommend the use of synbiotic (Active-MOS® + Bioplus 2BC®) in the farming of Nile tilapia PL with recurrent outbreaks of bacterial diseases during the sex reversal phase.     

ELECTRICITY AND PROPANE CONSUMPTION OF A SHRIMP HATCHERY IN THE STATE OF BAJA CALIFORNIA SUR,MEXICO

The consumption of electricity and propane for producing larvae and postlarvae of the whiteleg shrimp (Litopenaeus vannamei) was examined in a commercial shrimp hatchery on the Baja California Peninsula of Mexico. Between January and August 2005, 6 × 10⁶ postlarvae (average age PL16) were produced from 1.43 × 10⁹ nauplii. During that production period, the hatchery used 2.48 × 10⁹ kcal of fossil fuel energy (30% for electricity, 70% for liquid propane), which was equivalent to 16% of the operating costs. Electricity was used mainly for larval and postlarval rearing (36% and 10%) and microalgae culture (27%). During this production period, 1.47 × 10⁹ kcal of propane were consumed for heating daily more than 600 m³ seawater daily. Of that total, 33% was used for broodstock maintenance, 65% for larvae culturing, and 2% for postlarvae rearing. With increasing costs for shipping postlarvae to the mainland Mexican coastal areas (15% of operating costs) and the need to remain competitive with hatcheries in the coastal areas of Sonora and Sinaloa, alternative energy sources to reduce overall operational costs in hatcheries of Baja California Sur are discussed.     

Investigation of the Protective Effect of β-carotene in the Prevention of Lipid and Protein Oxidation in Carp Meat during Different Storage Times

ABSTRACT

This study was aimed to investigate the effects of dietary β-carotene supplement for 42 days on lipid and protein oxidation biomarkers in carp meat at different times of storage. Seventy-five fish were divided into three groups: group 1 as control group was fed with basic diet; groups 2 and 3 received 50 and 100 mg kg^?1 diet β-carotene, respectively. Based on the present study results, muscle malondialdehyde concentrations were significantly lower following β-carotene consumption at 0, 24, 72, and 96 h after harvest in group 3 compared to the control group (p < 0/05). Muscle protein carbonyl contents showed a significant decrease following β-carotene supplementation at 0, 48, and 96 h after harvest in group 3 compared to the control group. Ferric reducing antioxidant power values were significantly increased following β-carotene supplementation at 72 and 96 h after harvest in group 3 compared to the control group. The results indicated that β-carotene supplementation with a dose of 100 mg kg^?1 diet is largely effective to improve the oxidative status of carp meat by reducing lipid and protein oxidation.     

Assessment of AquaMats for removing ammonia in intensive commercial Pacific white shrimp Litopenaeus vannamei aquaculture systems

AquaMats are high surface–area polymer filters whose use produces higher yields with reduced health risks for the aquaculture product. We used AquaMats in pilot-scale systems and in intensive commercial Pacific white shrimp Litopenaeus vannamei production systems to stabilize and improve water quality by removing ammonia. In the pilot-scale systems, evaluation of the effects of temperature and hydraulic retention time (HRT) on ammonia removal rate indicated that the surface total ammonia nitrogen (TAN) conversion rate (STR, mg TAN/m²-day) increased with increasing temperature and decreasing HRT. The highest STR of 319.8 mg TAN/m²-day was observed at a temperature of 30 °C and a HRT of 5 min. In the commercial shrimp production systems, ammonia levels were significantly greater in the control systems (without AquaMats) than in the treatment systems (with AquaMats) after 6 days (P < 0.05). Results suggested that eight 150 cm × 90 cm pieces of AquaMats (0.057 m² surface area per m³ culture volume) were sufficient for promoting nitrification in this system. The growth rate of juvenile shrimp was most enhanced in treatment C (with 12 pieces of AquaMats, 0.085 m²/m³), which exhibited a significant decrease in ammonia.     

Determination of the optimal feeding rate and light regime conditions in juvenile burbot, Lota lota (L.), under intensive aquaculture

The aim of the study was to optimize burbot juveniles rearing in recirculating aquaculture system. In experiment 1 (17 °C, photoperiod 24L:0D), the fish (initial: body weight [W] = 15.36 ± 3.72 g, standard length [SL] = 12.48 ± 1.09 cm) were divided into four groups (I, II, III and IV). Different feeding levels were applied: 1, 2, 3 and 4 % of biomass daily (counted based on dry feed weight). The feed conversion ratio (FCR) and specific growth rate (SGR) were recorded. In experiment 2 (17 °C, feeding level of 2 % of biomass day^?1), fish (W = 5.24 ± 2.43 g and SL = 8.54 ± 1.24 cm) were divided into two groups where different light conditions were applied (I: 24 h light [1,800 lx] and II: 24 h darkness [4 lx]). In experiment 1, the highest SGR was recorded in group II (1.93 % day^?1), whereas the lowest SGR (1.27 % day^?1) and final W (P < 0.05) was in I group. The lowest (P < 0.05) FCR (0.63) was in group II. In the remaining groups, FCR was similar (0.68–0.70, P > 0.05). The feed consumption in group I reached 100 %, in group II, it was 71.3 % (P < 0.05) and it was the lowest in groups III (39.26 %) and IV (36.93 %). In experiment 2 no differences in the growth and survival rate were recorded (final SL between 14.16 and 14.19 cm, P > 0.05; W between 23.33–23.35 g; P > 0.05). The results from experiment 1 indicate that the feeding 2 % of biomass day^?1 was the most efficient. Also, it was proven, for the first time, that there was no effect of using different constant light conditions.     

Carbon, nitrogen and phosphorus budget in shrimp (Penaeus monodon) culture ponds in eastern India

Nutrient budget for shrimp (Penaeus monodon) culture was performed in ten culture ponds (0.4–1.0 ha) in Orissa, India, at stocking density of 10.0–22.10/m². The average initial body weight of shrimps was 0.02 g. The culture period was for 4 months. Feed was the main input of nitrogen (N), phosphorus (P) and organic carbon (OC). The FCR varied from 1.35 to 1.75. At harvest time, the average weight of shrimps varied from 28 to 32 g. Total N, P and OC applied to these ponds through all the inputs ranged from 106.64 to 292.63, 23.17 to 57.55 kg and 763.10 to 1,831.20 kg per crop, respectively. Feed alone accounted for 94.43–95.03 % total N, 91.92–95.36 % total P and 80.33–92.48 % total OC, respectively. The harvest of shrimp accounted for recovery of 25.45–36.88 (av. 30.12) %, 10.07–12.94 (av. 11.16) % and 15.80–20.81 (av. 18.01) % of added N, P and OC, respectively. N, P and OC accumulated in sediment were 49.11, 64.07 and 64.82 %, respectively, of total nutrient retention in the culture system. Unaccounted N, P and OC were 13.29, 21.83 and 18.14 %, respectively, of the total nutrient retention in the system. N, P and OC outputs in the discharged water during harvest were 7.48, 2.94 and 2.03 %, respectively.     

Development of phototaxis in the early life stages of Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

We investigated the development of phototaxis in larval and early juvenile stages of Pacific bluefin tuna Thunnus orientalis to detail behavior development in relation to light. We observed the distribution of Pacific bluefin tuna in an illumination gradient tank from 1 to 26 days after hatching (DAH). Two long rectangular tanks (100 × 10 × 10 cm) were used for experiments; each tank was divided into four sections for observations and one tank was equally illuminated at 1.0 × 10³ lx as the control tank, and the other was at 4.0 × 10², 1.0 × 10³, 1.0 × 10⁴ and 7.0 × 10⁴ lx as the illumination gradient tank. Laboratory-reared larvae and juvenile were released into each tank and acclimatized for 10 min. Thereafter, the number of individuals in each section was counted for 5 times with 10-min intervals. Until 2 DAH (3.6 ± 0.1 mm BL), larvae distributed homogeneously in each section in both tanks. After 3 DAH (3.7 ± 0.1 mm BL) when the eyes of the larvae were pigmented, most fish moved into the 7.0 × 10⁴ lx section in the illumination gradient tank, while fish in the control tank maintained a uniform distribution during the experimental period (Chi-square test, P < 0.05). The results suggest that the post-larvae and juvenile stages show strong positive phototaxis.     

Combined influence of water temperature, salinity and body size on energy budget in the sea cucumber Apostichopus japonicus Selenka

The worldwide demand for sea cucumber is outpacing the sustainable harvest capabilities of fisheries. Sea cucumber ranches and farms are striving to supplement wild harvest, but variable temperature and salinity conditions in pond culture systems make sea cucumber production challenging. In this study, we evaluated how water temperature, salinity and body size affected the energy budget of pond-cultured sea cucumber Apostichopus japonicus Selenka. An orthogonal design was used to identify the most suitable conditions for energy consumption and scope for growth (SFG). After the 42-day experimental period, we found that water temperature, salinity and body size significantly influenced energy consumption, while salinity and body size were the main influencing factors on SFG. Based on these results, we suggest that a water temperature of 16 °C and a salinity of 30 g L^?1 are optimal conditions for stocking sea cucumber A. japonicus with a body size of 37.34 ± 4.63 g. As such, the optimum stocking seasons for sea cucumber A. japonicus may be April in the spring and October in the autumn.     

Mercury and methyl mercury concentration in sediment,benthic, Barbus Grypus and pelagic,Barbus esocinus fish species,from Musa estuary,Iran

The concentrations of mercury (Hg) and methyl mercury (MeHg) in sediment and tissues of Barbus grypus and Barbus esocinus fish species from Musa estuary, north part of the Persian Gulf, were measured. The order of Hg and MeHg concentrations in the sediment and tissues of the fish species was as follows: liver > gill > muscle > sediment. In the tissues of two fish species, the Hg and MeHg concentrations were highest in liver whereas lowest in the muscle. In the sediment, mean concentrations of Hg and MeHg were 0.83 and 0.437 µg g^?1. Mean concentrations of Hg and MeHg in B. grypus were 1.2–0.624 µg g^?1 and in all tissues of B. esocinus were 0.75 and 0.421 µg g^?1. Significant correlation between heavy metal concentration in sediment and fish may be related to high variability of heavy metal in the sediment.     

Dietary arginine requirement of fingerling Indian catfish (Heteropneustes fossilis, Bloch)

An 8-week feeding trial was conducted to determine the dietary arginine requirement of fingerling Indian catfish, Heteropneustes fossilis (6.25 ± 1.30 cm, 4.8 ± 0.65 g). Six isonitrogenous (400 g Kg^?1) and isoenergetic (17.90 kJ g^?1) amino acid test diets were formulated with gradation of 2.5 g Kg^?1 containing graded levels of l-arginine (8.5–21.0 g Kg^?1, dry diet). Fish were randomly stocked in triplicate groups, in 75-l circular trough with flow-through system and fed experimental diets at 4 % BW/day at 0800 and 1800 h. Maximum live weight gain (277 %), best feed conversion ratio (FCR) (1.52) and protein efficiency ratio (PER) (1.64) were obtained in fish fed diet containing 16.0 g Kg^?1 arginine. However, quadratic regression analysis of live weight gain, FCR, PER and body protein deposition (BPD) data indicated requirements for dietary arginine at 16.80, 16.30, 16.11 and 16.10 g Kg^?1 of dry diet, respectively. Significantly (p < 0.05) higher whole body protein content, minimum carcass moisture and intermediate carcass fat contents were recorded at 16.0 g Kg^?1 dietary arginine diet. Ash content remained insignificantly (p > 0.05) low among all the treatments except at diet I and diet II. Based on the above results, it is recommended that the diet for young H. fossilis should contain arginine at 16.32 g Kg^?1, dry diet, corresponding to 40.80 g Kg^?1 dietary protein for optimum growth and efficient feed utilization.     

Mortality,hematology, and histopathology of common snook Centropomus undecimalis (Perciformes: Centropomidae) exposed to acute toxicity of ammonia

This study aimed to evaluate the tolerance of common snook Centropomus undecimalis larvae and juveniles exposed to acute concentrations of un-ionized ammonia for 96 h at 35g L^?1 salinity, after 24 h starvation. For that, 10 larvae (20.85 ± 1.46 mm) of 47 days post hatch (DPH) per experimental unit (1.5 L) were exposed to 0.00 ± 0.00, 0.65 ± 0.04, 1.29 ± 0.09, 2.59 ± 0.18, 3.88 ± 0.27, 5.17 ± 0.34, and 6.47 ± 0.43 mg L^?1 NH₃, in triplicates, at 26.72 ± 0.08°C, dissolved oxygen at 5.72 ± 0.10 mg L^?1 and pH 8.45 ± 0.06. During this period, no mortalities were observed. Another trial was performed with five juveniles (20.35 ± 6.10 g, 13.90 ± 1.75 cm) per experimental unit (60 L) exposed to 0.00 ± 0.00, 2.26 ± 0.07, 2.68 ± 0.11, 3.20 ± 0.13, 3.68 ± 0.17, and 4.27 ± 0.16 mg L^?1 NH₃, in triplicates, at 21.90 ± 0.76°C, dissolved oxygen at 6.27 ± 0.21 mg L^?1 and pH at 8.38 ± 0.04. Fish mortality increased as ammonia concentrations increased at each day, and LC₅₀ 96 h was 3.52 mg L^?1 NH₃. Larvae were less sensitive than juveniles, demonstrating that the environmental toxicity of ammonia to common snook is influenced by age. Sublethal exposition to ammonia caused histological damages in gills of common snook juveniles and variation on glucose levels, hematocrit, and red blood cells number, showing negative effects on fish homeostasis. Moreover, compared to other species, the common snook has great resistance to ammonia.