Some effects of temperature and salinity on laboratory-reared eggs and larvae of Polydactylus sexfilis (Pisces: Polynemidae)

Effects of temperature and salinity on eggs and yolksac larvae of Polydactylus sexfilis (Cuvier and Valenciennes) were examined in laboratory experiments. Data on developmental rates as influenced by temperature are presented. Larval length at 95% yolksac absorption was maximized between 23.8 and 28.6°C. Based on the development of functional eyes and jaws, larvae were judged capable of feeding before the yolk was completely absorbed. Larvae incubated at intermediate temperatures also had larger amounts of yolk remaining when eyes and jaws were judged functional. Temperature and salinity effects on hatching success, survival at the end of the yolksac stage, and morphological abnormalities were studied in a 10 × 5 (temperature × salinity) array of treatments. In 34‰ sea water, normalized larval survival at the end of the yolksac stage was greater than 50% between temperatures of 21.9 and 28.0°C. Larval survival decreased at lower temperatures and salinities. Proportions of abnormal larvae increased at temperature and salinity extremes, and normal development was maximized between 26 and 34‰. Larvae (74 h after fertilization) were more tolerant to extreme high temperatures than were newly fertilized eggs. Upper salinity tolerance limits of 42-h larvae were greater at 26.2°C than at 23.5 or 29.2°C, and lower salinity was less tolerated at the two extreme temperatures. Based on the results, recommended temperatures and salinities for rearing P. sexfilis eggs and early larvae are 24–28°C and 26–34‰.     

Dopamine modulates the physiological response of the tiger shrimp Penaeus monodon

Levels of glucose, lactate, pO₂, pCO₂, HCO₃⁻, TCO₂, Na⁺, K⁺, Cl⁻, protein, and oxyhemocyanin in the hemolymph and its osmolality and pH were measured when tiger shrimp, Penaeus monodon (13.5 ± 1.5 g body weight), were individually injected with saline or dopamine at 10^− 8, 10^− 7, or 10^− 6 mol shrimp^− 1. Results showed that hemolymph glucose, lactate, pCO₂, HCO₃⁻, and TCO₂ values increased from 2 to 4 h; hemolymph osmolality, Na⁺, and total protein had increased at 2 h; and hemolymph K⁺ decreased from 2 to 8 h after the dopamine injection. All physiological parameters returned to the control values 4–16 h after receiving dopamine. The dopamine injection also significantly decreased the oxyhemocyanin/protein ratio of P. monodon which occurred at 2 h, resulting from an elevation of hemolymph protein and a slight decrease of oxyhemocyanin. These results suggest that stress-inducing dopamine caused a transient period of modulation of energy metabolism, osmoregulation, respiration, and the acid–base balance in P. monodon in adapting to this environmental stress.     

Bacterial diversity of tilapia (Oreochromis niloticus) cultured in brackish water in Saudi Arabia

The bacterial flora occurring in brackish pond water, sediment, gills and intestine of healthy tilapia cultured in Saudi Arabia were estimated both quantitatively and qualitatively, and the isolates were identified to genus or species level. Total viable count of bacteria ranged from 1.4±1.5×10³ to 8.6±2.7×10³ cfu ml⁻¹; 1.2±3.1×10⁶ to 7.3±1.1×10⁷ cfu g⁻¹; 8.7±1.9×10⁵ to 2.1±0.9×10⁶ cfu g⁻¹; and 2.8±2.4×10⁷ to 1.0±1.6×10⁸ cfu g⁻¹ in the pond water, sediment, gills and intestine of brackish water tilapia, respectively. In total, 19 bacterial species were identified. The bacteria were predominantly Gram-negative rods (87%). Pond water and sediment bacteria influenced the bacterial composition of gills and intestine of tilapia. In contrast to gill bacteria, more diversification was observed in intestinal bacteria. The predominant (prevalence >10%) bacterial species were Vibrio parahaemolyticus, Vibrio carchariae, Vibrio alginolyticus, Chryseomonas sp., Vibrio vulnificus, and Streptococcus sp. in all the populations with the exception of the sediment population where Streptococcus sp. was replaced by Shewanella putrefaciens. Vibrio spp. (58% of the total isolates) dominated the total bacterial population.     

Filtration of king scallops (Pecten maximus)

Filtration rates of hatchery-reared king scallop (Pecten maximus L.) juveniles, fed a single species alga diet (Pavlova lutheri (Droop) Green), were measured at a range of temperatures (6–21 °C). Weight specific filtration rate (ml min⁻¹ g⁻¹ (live weight)) of juveniles of a selected size range of 17–19 mm shell height (0.26–0.36 g live weight) increased with temperature above 16 °C and decreased below 11 °C, but was not significantly different between these two temperatures. Measurements at 16 °C using juveniles with a wider size range of 10–25 mm shell height (0.05–0.8 g live weight) gave the allometric equation: filtration rate (ml min⁻¹)=12.19×weight (g)^0.887. Filtration rate decreased significantly when the cell concentration was greater than 200 cells μl⁻¹ (4.25 mg (organic weight) l⁻¹). With six other algae food species, filtration rates similar to those with P. lutheri were only achieved with Chaetoceros calcitrans (Paulsen) Takano. All other algae species tested were cleared from suspension at significantly lower rates. Experiments with diet mixtures of P. lutheri and these other algae suggested that this was usually a reflection of lowered filtration activity, rather than pre-ingestive rejection of cells. In experimental outdoor nursery rearing systems, the filtration rate was inversely proportional to the concentration of cells in the inflow, in the range 5–210 cells μl⁻¹. It was not affected by flow rate (2–130 l h⁻¹, equivalent to 0.12–28.38 l h⁻¹ g⁻¹ (live weight)) with scallop juveniles stocked from 2 to 62 g l⁻¹. The results are discussed in relation to on-growing scallops at field sites.     

Development of a specific pathogen free population of the Chinese fleshy prawn, Fenneropenaeus chinensis: Part II. Secondary quarantine

The Oceanic Institute (OI), in collaboration with researchers from the University of Arizona (UAZ), established a population of specific pathogen free (SPF) Fenneropenaeus chinensis through Secondary Quarantine (SQ) in Kona, Hawaii. Shrimp were 0.38 g (S.D. ± 0.13 g) when they entered the nursery/growout module of the SQ facility. Juveniles from five maternal families were stocked in separate 230-L nursery tanks, as was a sixth family comprised of shrimp from two of the seven original spawns. After tagging, representative shrimp from all six families were stocked in a 50-m² concrete raceway that was enclosed in a biosecure greenhouse. After 155 days in the growout module, mean shrimp weight was 23.4 g (S.D. ± 7.25 g) and females (29.1 ± 4.61 g) were 74% larger than males (16.7 ± 2.44 g). A Sprung Structure™ was erected to enclose the biosecure maturation and hatchery module of the SQ facility. Broodstock were subjected to an acclimation process where they were kept in seawater at 22 °C, followed by a reduction in water temperature of 1 °C/day until the temperature reached 17 °C. At this time, unilateral eyestalk ablation was performed on female broodstock and water temperature was further reduced at the same rate until it reached 12 °C. After 2 weeks, water temperature was raised to 17 °C at a rate of 1 °C/day to induce ovarian development. Production of an F₁ generation of Fe. chinensis was successfully accomplished using artificial insemination, and representative shrimp from this generation have tested negative for all specifically listed pathogens using histology and PCR/RT-PCR. Of particular interest with Fe. chinensis is their cold tolerance. This species may represent a valuable resource for shrimp farmers in temperate and sub-tropical climates to grow a second “winter” crop, thereby increasing production and profitability for the shrimp farmer.     

Efficacy of bithionol as an oral treatment for amoebic gill disease in Atlantic salmon Salmo salar (L.)

This study examined the efficacy of bithionol as an oral treatment for Atlantic salmon Salmo salar affected by amoebic gill disease (AGD). The current commercial management strategy of AGD is a costly 3 h freshwater bath. It is labour intensive and the number of baths needed appears to be increasing; hence, there is an effort to identify alternative treatments. Efficacy was examined by feeding AGD-affected Atlantic salmon twice daily to satiation with bithionol, an antiprotozoal, at 25 mg kg^− 1 feed. Three seawater (35‰, 17 °C) re-circulation systems were used each consisting of three tanks containing 32 Atlantic salmon smolts with an average (± SEM) mass of 90.4 g (± 5.2). Three feeds were examined in the trial including bithionol, plain commercial control and oil coated commercial control. Feeding commenced 2 weeks prior to exposure to Neoparamoeba spp. at 300 cells L^− 1 and continued for 28 days post-exposure. Efficacy was determined by examining gross gill score and identifying percent lesioned gill filaments twice weekly for 4 weeks post-exposure. Bithionol when fed as a two-week prophylactic treatment at 25 mg kg^− 1 feed delayed the onset of AGD pathology and reduced the percent lesioned gill filaments by 53% and halved the gill score from 2 to 1 when compared with both the plain and oil controls during an experimental challenge. There were no palatability problems observed with mean feed intake of bithionol over the trial duration with fish consuming higher levels of the bithionol diet compared to both the oil and plain controls. This study demonstrated that bithionol at 25 mg kg^− 1 feed, when fed as a two-week prophylactic treatment for Neoparamoeba spp. exposure, delayed and reduced the intensity of AGD pathology and warrants further investigation as an alternative to the current freshwater bath treatment for AGD-affected Atlantic salmon.     

Evidences of the intertidal red alga Grateloupia turuturu in turning Vibrio parahaemolyticus into non-culturable state in the presence of light

Grateloupia turuturu, previously known as Grateloupia doryphora, has been widely reported to be an invasive algal species. There are no studies to relate the impact of its existence on its surrounding environment. In this paper, we present our results to show that about 70% of individuals collected from the field could turn Vibrio parahaemolyticus into non-culturable state on both selective (TCBS) and non-selective (2216E) culture medium in 24 h in the presence of light in live algal culture. Total bacteria counts on TCBS and 2216E plates dropped from the initial 565 (± 174) and 1192 (± 60) cfu ml^− 1 respectively to zero in 24 h. This effect disappeared when the alga was grown in darkness. The same effect was not found in two other intertidal macroalgae Laminaria japonica and Palmaria palmata. Further tests showed that the settlement ability of bacteria in seawater was impaired significantly in the presence of this alga in comparison with three other algal species.     

Effect of low water temperature on viral replication of white spot syndrome virus in Procambarus clarkii

This study evaluated the effect of low water temperature (10 ± 1 °C) on viral infection and replication of white spot syndrome virus (WSSV) in crayfish, Procambarus clarkii, under standardized conditions. Crayfish were (i) maintained at 24 ± 1 °C before challenge and 10 ± 1 °C afterwards, or (ii) maintained at 10 ± 1 °C before challenge and 24 ± 1 °C afterwards. No mortality was observed when crayfish were held at 10 ± 1 °C after challenge, but mortality reached 100% when they were transferred to 24 ± 1 °C. Competitive PCR showed that viral levels at 10 ± 1 °C rose from 10⁶ to 10⁸ copies/mg of gill tissues, while at 24 ± 1 °C levels increased from 10⁶ to 10¹⁰ copies/mg of gill tissues during the same time interval. These results showed that a low water temperature of 10 ± 1 °C could reduce viral replication when compared to 24 ± 1 °C but could not prevent it.     

Swimming behaviour of winter flounder (Pleuronectes americanus) on natural fishing grounds as observed by an underwater video camera

Swimming behaviour of winter flounder (Pleuronectes americanus) was recorded near baited hooks on natural fishing grounds using an underwater video camera. Winter flounder were observed to stay on or very close to the seabed, never rising to more than 0.6 m off bottom during 1 month of observation. Winter flounder were recorded to take bait actively at temperatures as low as −1.2 °C. Movement of winter flounder was characterised by a period of swimming off seabed followed by a period of resting on the seabed. The proportion of time swimming off seabed as opposed to resting on the seabed was positively related to water temperature. Flounder spent an average of 32% of time in swimming when at −1.2 °C compared with 67% when at 4.4 °C. Voluntary swimming speed of the flounder during the period of swimming was lower at lower temperatures. An average swimming speed of 0.52 body lengths per second (L s⁻¹) at −1.2 °C was recorded compared with 0.95 L s⁻¹ at 4.4 °C. Overall rate of movement was reduced by three-fold when water temperature fell from 4.4 to −1.2 °C. The reduced rate of movement at lower temperatures is discussed in relation to potential fishing area of fixed fishing gears such as gillnets.     

The effects of the decomposition of mangrove leaf litter on water quality, growth and survival of black tiger shrimp (Penaeus monodon Fabricius, 1798)

An experiment was conducted for 8 weeks at the Cantho University, Vietnam, to determine the acceptable level of mangrove leaf litter load and its effect on water quality, growth and survival rate of tiger shrimp (Penaeus monodon). Shrimps were cultured in plastic tanks containing 50 L of brackish water (salinity of 15‰). Leaf litter of Rhizophora apiculata, Avicennia officinalis, Excoecaria agallocha and Acacia auriculiformis were loaded to tanks at rates of 0.0 (control), 0.125, 0.25, 0.5, 1.0 and 2.0 g L^− 1 with and without aeration. Tiger shrimp post-larvae (PL; 0.05 ± 0.01 g) obtained from the shrimp hatchery of Cantho University were stocked at a density of 20 PL per tank and fed with pelleted feed containing 38% protein at a rate of 10% body weight (BW) day^− 1.

The high leaf-loading rates significantly reduced dissolved oxygen (DO) and survival rates of shrimp in the non-aerated treatments, and all shrimps died after 2 days in the treatments with loading rates above 0.5 g L^− 1. Leaf litter loads significantly increased tannin content, chemical oxygen demand (COD), H₂S and pH in the aerated treatments. Stepwise regression analysis showed COD, tannin and H₂S concentrations had negative effects on shrimp growth in the aerated treatments. Tannin concentration was found to be highest in the treatments with Excoecaria (32 mg L^− 1) and Avicennia (24 mg L^− 1) leaves. However, there were no significant differences in growth and survival rates of shrimp among the aerobic treatments loaded with different leaf types. The results of this study showed that moderate load of mangrove leaves could play an important role in promoting shrimp growth and survival in aerobic condition. Mangrove leaves at a loading rate of 1 g L^− 1 positively influenced both the survival and growth rate of shrimps.     

Seawater adaptation and growth of post-smolt Atlantic salmon (Salmo salar) of wild and farmed strains

Atlantic salmon smolts (Salmo salar L.) of wild (Namsen) and farmed (AquaGen) strains were transferred to full-strength seawater (33‰) for 0 (initial control group), 0.5, 1, 2, 4, 8, 14, 30, 42 and 60 days at three different temperatures (4.3, 9.4 and 14.3 °C). Freshwater temperature in each tank was adjusted to test conditions 10 days prior to transfer. Physiological adaptation was monitored as changes in plasma growth hormone levels, gill Na⁺,K⁺-ATPase activity, plasma chloride levels and survival in seawater. Overall, smolts from the wild strain were better able to tolerate transfer to seawater than smolts from the hatchery strain. A delay in the osmotic disturbance and a prolonged period of osmotic stress were observed at the low temperature. Circulating GH levels increased transiently in all groups during the first 12–48 h in seawater and long-term GH levels were positively correlated with seawater temperature. Growth rates were influenced by temperature and strain, with the farmed smolts showing a higher growth than the wild smolts. Food Conversion Efficiency (FCE) was higher in smolts from the farmed strain, whereas no differences in daily food consumption were observed. Optimum temperature for FCE was calculated to be 10.5 °C, whereas the optimal temperature for growth in seawater was calculated to be 13.0 °C. We suggest that the observed differences in seawater tolerance, growth and food conversion probably are genetic and may reflect the fact that the hatchery fish have been bred for rapid growth for several generations.     

Shipping studies with juvenile and adult Malaysian prawns Macrobrachium rosenbergii (de Man)

Four studies examined shipping factors of packing technique, density, duration, type of water and use of habitat material for shipping juvenile and adult prawns Macrobrachium rosenbergii. Prawns were shipped in double polyethylene lined 38 × 38 × 20 cm deep styrofoam boxes containing oxygenated water. At temperatures of 19–20°C, 17 g prawns could be shipped safely for 42 h at a density of 10–12 prawns per box (12–15 g liter⁻¹ shipping water). Juveniles, mean size about 6 g, could be shipped at a density of 40 per box (18 g liter⁻¹) for 24 h or 20–25 per box (9–11 g liter⁻¹) for 48 h. Use of mesh material to increase surface area in the box did not appear beneficial nor did shipping in brackish water (salinity8‰). Adults packed unrestricted resulted in survival rates substantially higher than those obtained from immobilized prawns wrapped in mesh.

During the shipment, pH and dissolved oxygen concentrations decreased whereas ammonia concentrations increased. The decreased pH levels may have reduced the ammonia toxicity by decreasing the amount of toxic unionized ammonia (NH₃) in solution. In general, dissolved oxygen concentrations appeared more closely related to survival rates than did other water quality parameters which were measured.     

Salinity tolerance of cultured Eurasian perch, Perca fluviatilis L.: Effects on growth and on survival as a function of temperature

Eurasian perch is generally only considered to be a candidate for freshwater aquaculture even though wild populations are found in estuarine and brackish water habitats. Little knowledge exists on two issues a) the effect of temperature on the salinity tolerance of perch and b) the long-term effects of brackish water on their overall growth performance. The present study addresses these two questions.

Firstly, the effect of temperature (12, 15, 20 and 25°C) on perch survival of a salinity challenge at either 13 or 18‰ was determined. Survival was unaffected by 13‰ at the two lowest temperatures whereas higher temperature and higher salinities had a dramatic detrimental effect (at 25°C, 50% mortality was reach at 62h and 39h for 13‰ and 18‰, respectively). Secondly, we examined the effect of salinity on growth, which was assessed by measuring standard length and body weight at regular intervals for 130days. In addition, Specific growth rate (SGR), Fulton's condition factor (K) and food conversion ratio (FCR) were also calculated as was the effect of salinity on plasma osmolality, blood ion content (Na⁺, Cl⁻, K⁺) and muscle water content at the termination of the experiment. The optimum growth for this study was seen in the lowest salinities at 0 and 4‰. Surprisingly, even small increases in salinity were detrimental to perch growth. At 10‰, growth in terms of body weight was reduced by about 50% after 130days compared to perch reared in freshwater.

Interest in brackish water production of perch would be most likely served best by selecting a strain of perch that is adapted to saline conditions, as found in the lower Baltic region. Further studies are required to understand the potential for brackish water perch production.     

Breeding and juvenile culture of the lined seahorse, Hippocampus erectus Perry, 1810

All seahorse species worldwide have been placed under CITES Appendix II since 2004, because they have been over-exploited for traditional Chinese medicine and aquarium trades. Aquaculture has been recognized as a long-term solution for sustaining the seahorse trade while minimizing wild collection. In this study, we evaluated the breeding and juvenile culture of an important aquarium seahorse species, the lined seahorse Hippocampus erectus, Perry 1810. Pairing, mating and copulation behavior were observed. Gestation time and brood size were 17.33 ± 2.94 days and 272.33 ± 66.45 individuals/brood, respectively. Growth rates differed among juveniles from different broods. Effects of temperature on the growth rates and survivorship of the juveniles during the first two weeks were compared. The highest growth rate and survivorship of the juveniles occurred at 28–29 °C among the temperatures tested (24–33 °C). Growth rate and survivorship of the juveniles during the first 9 weeks at 28 °C were investigated. The final standard length and survivorship of the juveniles were 6.32 ± 0.52 cm and 71.11 ± 10.18%, respectively, and the relationship between the wet weight and the standard length of the juvenile seahorses can be expressed as: W = 0.0034 L^2.5535 (r² = 0.9903, n = 12, P < 0.01). These findings suggest that H. erectus is a good candidate for commercial aquaculture.     

A soft technology to improve survival and reproductive performance of Litopenaeus stylirostris by counterbalancing physiological disturbances associated with handling stress

The consequences of handling stress (fishing, transfer, eyestalk ablation) on shrimp broodstock are poorly documented. The weakness of farmed shrimp, Litopenaeus stylirostris, during winter is a major problem in New Caledonia, because of seasonal climate (tropical–sub-temperate). The transfer of broodstock in winter from earthen outdoor ponds to indoor maturation tanks in the hatchery (T = 20 °C, Salinity = 35‰, fed shrimp) usually leads, after 48 h, to high mortality (up to 70%). Eyestalk ablation to induce ovarian maturation in females leads to further mortality.

Starting from a background analysis of physiological disturbances (initial osmoregulatory imbalance) associated with handling stress (Wabete, N., Chim, L., Lemaire, P., Massabuau, J.-C., 2004. Caractérisation de problèmes de physiologie respiratoire et d'échanges ioniques associés à la manipulation chez la crevette pénéide Litopenaeus stylirostris à 20 °C. Styli 2003. Trente ans de crevetticulture en Nouvelle-Calédonie. Ed. Ifremer. Actes Colloq. 38, 75-84.), we developed a protocol using a soft technology, based on modifications of water salinity, temperature and feeding regime. The aim was to minimize problems of osmoregulatory imbalance and associated mortalities. The protocol we developed, called the LSD OT protocol (Low Salinity and Diet, Optimal Temperature), was first evaluated on sub-adult shrimp (20–25 g) and then applied to broodstock. Survival after transfer and following eyestalk ablation, as well as reproductive achievement (spawning rate, nauplii number) was considerably improved when shrimps were transferred under “physiological comfort” i.e. warmed isosmotic water (26 °C and 26‰) and unfed for 3 d. This new handling protocol, based on a better control of salinity, temperature and feeding conditions, has been transferred successfully to private hatcheries and already contributes to an increased profitability of New-Caledonian shrimp industry.     

Effect of probiotics, Enteroccus faecium, on tilapia (Oreochromis niloticus) growth performance and immune response

The aim of this study was to analyze the effect of a probiotic bacterium, Enterococcus faecium ZJ4 on growth performances and immune responses of tilapia (Oreochromis niloticus). The tilapias were treated with E. faecium ZJ4 at a final concentration of 1 × 10⁷ cfu ml^− 1 in aquaria water every 4 days. Six aquaria with three replicates for treated and controls were used. After 40 days, the tilapias supplemented with the probiotic showed significantly better final weight and daily weight gain (DWG) than those fed the basal diet (Control) (P < 0.05). There was no remarkable difference (P > 0.05) in the total serum protein, albumin content, globulin concentration and A/G ratio between the treated and control tilapias. The result of lysozyme activity assay was similar to these biochemical indexes. However, the complement component 3 content, myeloperoxidase (MPO) activity and the respiratory burst activity of blood phagocytes were higher (P < 0.05) in E. faecium treated tilapias (trial 1) than the controls.     

Effects of temperature change rate on nitrogen effluxes of Macrobrachium rosenbergii (DeMan)

Ammonia-N (NH4⁺ + NH³) and total nitrogen (TN) efflux rates of Macrobrachium rosenbergii were measured during stepwise temperature changes (26 °C → 22 °C → 18 °C → 22 °C → 26 °C) at different rates. Sudden temperature reductions did not affect efflux rates, but sudden temperature rises evoked rapid and high increases in the efflux rates. A direct relationship between ammonia-N excretion and water temperature was observed when gradual temperature changes were effected over a 5 h period. When the animals were acclimated to a new temperature for 72 h, no clear effects of temperature on the efflux rates were found. Sudden temperature changes resulted in an increased proportion of ammonia-N in the total nitrogen excreted. It is suggested that temperature changes during the shipment of M. rosenbergii should be avoided or made gradually.     

Safety and efficacy of emamectin benzoate administered in-feed to Atlantic salmon, Salmo salar L., smolts in freshwater, as a preventative treatment against infestations of sea lice, Lepeophtheirus salmonis (Krøyer)

The safety and efficacy of emamectin benzoate, administered in-feed to Atlantic salmon smolts, Salmo salar L., held in freshwater, was evaluated as a preventative treatment against sea lice, Lepeophtheirus salmonis, following transfer of fish to seawater.

In the safety study, salmon smolts held in freshwater were fed with diets containing emamectin benzoate at nominal doses of 0 (control), 50 (recommended dose) and 250 (5× recommended dose) μg kg⁻¹ fish day⁻¹ for 7 days (days 0–6). Actual dose rates, based on measured concentrations of emamectin benzoate in feed, differences in fish weight, and feed consumed, were 0, 54, and 272 μg kg⁻¹ day⁻¹, respectively. On day 9, fish were transferred to seawater and observed for 14 days. No differences in feeding response, coordination, behaviour, gross and histological appearance were observed between control fish and those that received 54 μg kg⁻¹ day⁻¹. Among smolts that received 272 μg kg⁻¹ day⁻¹, approximately 50% exhibited darker coloration, and one fish (1%) exhibited uncoordinated swimming behaviour. No pathognomonic signs of emamectin benzoate toxicity were identified.

In the efficacy study, smolts held in freshwater were fed an unmedicated ration (control group) or emamectin benzoate at 50 μg kg⁻¹ day⁻¹ (treated group) for 7 days (days 0–6). On day 9, fish were re-distributed to eight seawater tanks, each holding 30 control and 30 treated fish. On days 28, 56, 77 and 109, respectively, control and treated fish in two tanks were challenged with L. salmonis copepodites. When lice in each group reached chalimus stage IV, fish were sampled and the numbers of lice were recorded. Fish challenged at day 109 were sampled for the second time when lice were at the adult stage. Efficacy was calculated as the reduction in the mean number of lice on treated fish relative to the mean on control fish. Treatment with emamectin benzoate resulted in an efficacy of 85.0–99.8% in fish challenged at days 28–77, from the start of treatment, and lice counts were significantly lower (P<0.001) on treated fish than on controls. When fish challenged at day 109 were sampled at day 128, efficacy was 44.3%, but survival of chalimus to adult lice on treated fish was lower, and at day 159, efficacy had increased to 73%. These results demonstrate that treatment of salmon smolts with emamectin benzoate in freshwater was well tolerated and highly effective in preventing sea lice infestation following transfer of fish to seawater.     

Furunculosis in Atlantic salmon (Salmo salar L.) is not readily controllable by bacteriophage therapy

The potential of bacteriophage therapy to control bacterial disease in farmed fish was tested using, as an example, furunculosis of Atlantic salmon, caused by Aeromonas salmonicida subsp. salmonicida.

In vivo testing with Atlantic salmon and rainbow trout (Oncorhynchus mykiss Walbaum) showed no adverse effects, with bacteriophage generally cleared within 96 h of administration by either intraperitoneal (i.p.) injection or oral in-feed.

Juvenile Atlantic salmon were administered a combination of bacteriophage O, R and B (1.9 × 10⁸ pfu fish^− 1) by i.p. injection, after they had been challenged with A. salmonicida subsp. salmonicida 78027, also by i.p. injection. The fish that were injected with bacteriophage immediately after challenge died at a significantly slower rate then those that were either not treated with bacteriophage, or treated 24 h post-challenge. However, the end result (100% mortality) was not affected.

In further experiments the effects of oral (1.88 × 10⁵ pfu g^− 1 fish^− 1 daily for 30 days), bath (1.04 × 10⁵ ml^− 1 daily for 30 days) and i.p. (6.25 × 10⁷ pfu fish^− 1) phage treatment to control furunculosis in experimentally infected Atlantic salmon were compared with antibiotherapy (treatment with 10 mg kg^− 1 bw^− 1 day^− 1 oxolinic acid for 10 days), using an indirect cohabitation challenge. No protection was offered by any of the bacteriophage treatments, compared to the positive challenge group, although significant protection was offered by the oxolinic acid treatment. Analysis of samples taken from the trials demonstrated that bacteriophage were correctly administered to the fish and, on occasion, were isolated from fish that had succumbed to furunculosis. It was also shown that bacteriophage resistant A. salmonicida subsp. salmonicida isolates could be recovered from mortalities in all the treatment groups.

The results suggest that, although there were no safety problems associated with the approach, furunculosis in Atlantic salmon is not readily controllable by application of bacteriophage.     

Purification and partial characterization of Cu, Zn superoxide dismutase from haemolymph of Oriental river prawn Macrobrachium nipponense

The copper plus zinc superoxide dismutase (Cu, Zn-SOD) was purified from haemolymph of the Oriental river prawn, Macrobrachium nipponense and partially characterized. Partial protein precipitation in crude extract was affected by using heat treatment and (NH₄)₂SO₄ fractionated precipitation methods. Fractionation of superoxide dismutase was performed by DEAE-cellulose 32 ion-exchange chromatography and followed by CM-cellulose cation-exchange chromatography. The molecular weight of it was about 66.1 kDa, as judged by SDS polyacrylamide gel electrophoresis. The enzyme was sensitive to cyanide and H₂O₂, and contained 1.08 ± 0.14 atom of copper and 0.98 ± 0.11 zinc per subunit shown in atomic absorption spectroscopy, which revealed that purified SOD was Cu, Zn superoxide dismutase. The purified enzyme had an absorption peak of 269 nm in ultraviolet region and the enzyme remained stable at 25–45 °C within 60 min. But it was rapidly inactivated at higher temperature (50 °C). The activity of purified shrimp Cu, Zn-SOD was remained stable over the range pH 5.8–8.3. Treated with 10 mM mercaptoethanol, the enzyme activity significantly increased. However, the enzyme activity was obviously inhibited by 10 mM CaCl₂, ZnCl₂, SDS, EDTA–Na₂ and 1 mM and 10 mM K₂Cr₂O₇. The results showed that it might be a kind of EC-SOD. And it was the first report of some characterizations of this EC-SOD in M. nipponense.