High incidence of death due to collision of hatchery-reared Pacific bluefin tuna Thunnus orientalis juveniles in sea cages, as revealed by head and spinal injuries

High mortality of hatchery-reared Pacific bluefin tuna (PBT) juveniles is frequently observed in sea cages after transfer from indoor tanks, and is likely due to collisions of the fish with the net wall of the sea cages. Because collisions frequently cause bone injuries due to physical impact, such injuries can be considered an index of obvious collisions. In the present study, bone injuries of dead juveniles were investigated in order to examine the prevalence of net collision as a cause of death among hatchery-reared PBT juveniles in sea cages. Juvenile PBT were reared in sea cages for 90 days after transfer, and dead fish were collected and examined by the clearing and staining method or by dissection to detect injury to the vertebral column and parasphenoid. The prevalence of injuries to the vertebral column and parasphenoid until day 30 after transfer was low (0.0–12.0 %) when the fish were 5.5–15.2 cm in total length (TL). However, it drastically increased to 17.8–78.0 % for fish 21.0–39.2 cm TL from day 31 onward after transfer. These results suggest that the mortalities of juvenile PBT larger than 20 cm TL in cages were induced by net collisions.     

Improving rearing performance in sea‐cage culture of Pacific bluefin tuna Thunnus orientalis juveniles (Temminck and Schlegel) using small sea cages

High levels of mortality occur in large net‐cage culture of Pacific bluefin tuna (PBF) Thunnus orientalis due to poor growth on commencement of sea‐cage culture obstructing the mass production of fingerlings. Therefore, we carried out this study to develop a countermeasure by using small sea cages (square with 13‐m sides). PBF juveniles were directly transferred to a 30‐m‐diameter cage (control) and compared them to fish transferred to small sea cages for 12 days before being merged into another 30‐m‐diameter cage. The survival rate, growth performance and potential factors increasing mortality were examined. The results of our study showed that survival rate in small sea cages was approximately 20% higher than that of the control. Poor growth also occurred in the small sea cages; however, its frequency and daily mortality rate were half those in the control. In addition, growth performance such as specific growth rate and weight gain of PBF juveniles in small sea cages significantly increased compared to the control. These results suggest that using small sea cages could be an effective countermeasure for poor growth, which may mitigate the high‐mortality conditions of current sea‐cage culture systems for PBF.     

Mortality of Northern Bluefin Tuna Thunnus thynnus Due to Trauma Caused by Collision During Growout Culture

Abstract.— Indoor and outdoor experiments were conducted to improve the rearing techniques for artificially hatched northern bluefin tuna Thunnus thynnus during growout culture. Collisions with the walls of tanks or nets caused mass mortality that occurs during growout. The period when collisions frequently occur and the types of injury caused by collision were examined in this study. Juveniles were reared in indoor tanks from 30 to 120 d after hatching, and in an open sea net cage from 42 to 150 d after hatching. Dead fish were collected and counted daily in both of the experiments. In the indoor experiment, the sampled fish were preserved in 10% formalin solution, and each of 10 specimens of about 30, 50, 70, 85, 100, 130, 160 and 225 mm in body length (BL) were examined using x‐rays to detect injury of the bones. Juvenile and young adult bluefin tuna showed a reduction in numbers caused by collision with the tank or the net wall during the experiments. In the indoor tank, there were 1,200 fish on day 30 but only eight on day 120. The daily mortality increased from day 30 after hatching, when juveniles reached 50‐mm BL and remained over 4%/d until day 60 when juveniles grew to 300‐mm BL. The proportion of dead fish with injuries of bone, especially of the vertebral column and the parasphenoid, increased after fish reached 50‐mm BL, and exceeded 60% in fish with BL 85 mm or greater. In the open sea net cage, there were 3,841 fish at the start of the experiment on day 42 and only 65 on day 150. In this experiment, the reduction was greatest from the start of the experiment until day 80, when fish grew to approximately 25 cm in total length. Significant bacterial, viral or parasitic diseases were not observed in these fish; the only findings were dislocations of the vertebral column and injuries to the upper and lower jaws. These results show that the loss of juvenile and young adult bluefin tuna was caused by collision with the tank or net wall that fatally damaged the bones of the vertebral columns and the parasphenoid.     

Optimal periods of night‐time lighting in the sea cage culture of Pacific bluefin tuna,Thunnus orientalis,juvenile (Temminck and Schlegel)

We have previously reported that night‐time lighting prevents the mass death of Pacific bluefin tuna (PBT) juvenile due to collision and/or contact with the walls of sea cages, immediately after transfer to the cages, and that night‐time lighting does not negatively impact fish stress levels. However, the period of night‐time lighting should be limited to minimize negative impacts on the surrounding environment and aid management. Therefore, we investigated the optimal period of night‐time lighting by evaluating the whole‐body cortisol and glucose levels as stress parameters, growth performance and survival of PBT juvenile in four cages with different periods of night‐time lighting (i.e. unlit, 4‐day, 8‐day and 12‐day lighting). The results showed that almost all fish were died 1 day after transfer to the unlit cage. In comparison, the other groups (4‐day, 8‐day and 12‐day lighting) had high survival rates (92.5–96.0%) without significant difference. However, in the 4‐day‐lighting group, an obvious stress response was recorded on day 5, and growth performance was significantly lower. In the 8‐day‐lighting group, whole‐body cortisol levels were slightly elevated on day 9; however, significantly elevation was not recorded on day 12. These results indicate that the recommended lighting period of night‐time lighting in sea cages is 8–12 days.     

Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle

Tuna aquaculture is currently dependent on the wild capture of juveniles for production. The development of hatchery technology for bluefin and other tunas would be a major step forward in improving sustainability of their aquaculture. The present study overviews the technology in the life cycle completion of the Pacific bluefin tuna (PBT) Thunnus orientalis (Temminck et Schlegel) under aquaculture conditions in Kinki University, and the problems to be solved for the establishment of tuna hatchery technology. On 23 June 2002, broodstock of PBT that were artificially hatched and reared spontaneously spawned in captivity. The resulting eggs hatched and were subsequently reared to the juvenile stage. The spawning fish were the result of a research project started in 1987 to rear wild‐caught juvenile PBT that were several months old. Fertilized eggs were obtained from these fish in 1995 and 1996. Resulting juveniles (the artificially hatched first generation) were reared to maturity and spawned in 2002. Over the summer of 2002, 1.63 million eggs from these fish were used for a mass rearing experiment, and 17 307 juveniles were produced and transferred to an open sea net cage. Of these artificially hatched second‐generation PBT, 1100 grew to approximately 95 cm total length and 14 kg body weight in 22 months. This procedure means the completion of PBT life cycle under aquaculture conditions, which was first attained among large tuna species. The problems awaiting solution in PBT hatchery production are their unpredictable spawning in captivity, to improve survival during the first 10 days post hatch, to reduce cannibalism in larval and juvenile stages, and to solve collision problem causing high mortality during the juvenile stage.     

Efficacy of Sarafloxacin Hydrochloride in Treating Naturally-Induced Edwardsiella ictaluri Infections in Channel Catfish,Ictalurus punctatus

Sarafin (sarafloxacin hydrochloride), a new antibacterial, was evaluated in the field on a naturally induced infection of Edwardsiella ictaluri in channel catfish, -Ictalurus punctatus. Healthy channel catfish (mean weight = 50 g) were stocked into nine cages at 200 fish per cage in a pond with an undergoing E. ictaluri infection. Seven days after stocking, dead fish were observed in the cages with clinical signs of enteric septicemia of channel catfish (ESC). After E. ictaluri was confirmed through isolative biochemical tests, medicated feed was applied for five consecutive days. During this period, fish in three control cages received a commercial 32% protein floating feed, three other cages of fish served as positive controls and were fed Romet, and three cages received the test feed with Sarafin. Both medicated feeds reduced the increase in cumulative percent mortality. In the control cages, cumulative percent mortalities continued to increase throughout the study period. Average daily mortality rates were significantly lower following both treatments of medicated feed, and treatments receiving Sarafin showed the greatest reduction in average daily mortality rates. Average daily mortality rates in the control did not change after the medicated feeding period. Toward the end of the study, temperatures reached 30°C, above the active range of ESC infections, and all mortalities ceased.     

Use of night-lights to attract food organisms into tropical marine fish cages

Abstract. A 91-day cage trial was conducted with juvenile seabass, Lates calcarifer (Bloch), and grouper, Epinephelus tauvina (Forskal), to ascertain the capacity of kerosene pressure lamps and fluorescent electric lamps as night-lights above the cages to attract pelagic food organisms into the cage and consequently sustain the survival and growth of the cultured fish. The experiment was conducted using 1×1×1·5m floating cages with three different net mesh sizes (1, 13, and 19mm) and four fish stocking densities (seabass—10, 20,30 and 40/m³; grouper —10/m³). A positive growth response and survival was observed with seabass and to a lesser extent with grouper with increasing net mesh size and decreasing fish stocking density. At the lowest tested density of 10 fish/m³ seabass survival increased from 5·0 to 95·0% and total cage fish biomass increased from −95·1% to +56·9% with an increase in net mesh size from 1 to 19mm over the 91-day culture trial, respectively. The results are discussed in relation to the current commercial marine finfish cage farming practices employed in Indonesia.     

Effects of restricted feeding on growth of red sea bream and sedimentation of aquaculture wastes

For improving the economic and environmental sustainability of fish farming, it is necessary to optimize feeding regimes. From this viewpoint, we monitored the growth and mortality of red sea bream (Pagrus major), C and N fluxes and sediment chemistry at 2 commercial fish cages; cage 1 (conventional satiation feeding) and cage 2 (restricted feeding: same feeding frequency but 18% reduction in the feed amount) for 276 days. The similar specific growth rates (0.43% in cage 1 and 0.39% in cage 2) but different feed conversion efficiencies (0.54 in cage 1 and 0.62 in cage 2) and mortality (> 2-times higher in cage 1) between the 2 cages, indicate overfeeding in cage 1 culture. Elemental and stable isotopic analyses of sediment trap materials enabled the quantification of waste feed- and fecal matter-derived organic matter (OM) separately. The results shows that (1) aquaculture-derived OM comprised most of the fish-farm settling OM, excluding the period from January to April, when natural OM often accounted for a half of the bulk OM, (2) there was a difference in the seasonal trend between the fluxes of waste feed and fecal matter, and (3) there were no differences in the percentage compositions and fluxes of waste feed and fecal matter between the 2 cages. The isotopic analysis showed that the waste feed-derived OM in the sediment below cage 2 was 24% less than that below cage 1, suggesting effect of restricted feeding. Determining the relative amount of waste feed and fecal matter in settling and sedimentary OM is an effective method to evaluate the optimum feeding regime.     

Effects of stocking density of Labeo rohita on survival, growth and production in cages

Labeo rohita (139.92 ± 0.76 mm/24.33 ± 0.45 g) was reared for 92 days in floating square cages (10 m² area, 1.5 m height) in a pond (2 ha) at six stocking densities (5, 7.5, 10, 15, 20 and 25 fish m^?2) each with 3 replicates. Fish were fed daily once in the morning with rice polish and groundnut oil cake (1:1) in dough form at 3 % of the total body weight. Survival ranged from 96 to 100 % in different stocking densities. Final average body weight, average body weight gain, mean daily body weight gain and SGR decreased (P < 0.05) with increasing stocking density. Conversely, final biomass, biomass gain and FCR increased (P < 0.05) with increasing stocking density. The highest growth rate of fish could be achieved up to 60 days at 5 fish m^?2 and 92 days at other densities. The reduced growth rate at 10–25 fish m^?2 for 60 days of culture indicated that stress is related to size and density of the fish, suggesting that utmost care is required to reduce the stress at high densities. Maximum production and profit was observed at the highest stocking density. Non-lethal levels of water and soil qualities at different sites (cage premises, and 20 and 200 m away from cage area) suggested that cage aquaculture could be done safely covering 0.9 % of pond area. Production of advanced fingerlings in cages was found a viable alternative to their culture in pond.     

Growth of Tilapia aurea in Seawater Cages

Fingerling Tilapia aurea were reared for 90 days in three 1.0 m³ floating cages in seawater (36 ppt) at Lee Stocking Island, Bahamas. Fish stocking density (100, 200 and 400 fish/m³) apparently did not affect growth rate but it appears salinity inhibited growth. Daily weight gain and specific growth rate (G) averaged 0.34 g/day and l.08%/day, respectively, for Tilapia aurea fingerlings. Infection of the Tilapia aurea by Bacillus sp. was associated with a significant number of mortalities. The relatively low growth rate and the high incidence of disease and mortality of Tilapita aures in seawater indicate that it may not be a good candidate for cage culture in full-strength seawater.     

饲料蛋白水平对宝石鲈增重和体成分的影响

用5种不同蛋白质水平(分别为30.89%、36.67%、40.08%、44.90%、49.14%)的饲料分别饲喂宝石鲈(Scortum bacoo)幼鱼25 d,每组3重复(每重复30尾鱼),室内网箱饲养试验结果表明:40.08%组的日增重、特定生长率显著高于30.89%组(P<0.05),饲料转化率极显著高于30.89%组(P<0.01);不同组间的肝体指数、脏体指数和肥满度无显著差异(P>0.05);饲料蛋白水平对宝石鲈幼鱼肌肉水分、粗蛋白、粗脂肪、灰分及肝脏的水分、粗脂肪无显著影响(P>0.05)。     

密度对网箱养殖硬头鳟生长及经济效益的影响

本文主要研究密度对网箱养殖硬头鳟Oncorhynchus mykiss存活和生长的影响。在水温8.2~19.1℃下,将体质量1.02 kg的硬头鳟鱼种养殖在5m×10m×6m网箱中,网箱放置在松花江上游的松山水库中,密度分别为5尾/m~2(Ⅰ组)、8尾/m~2(Ⅱ组)、11尾/m~2(Ⅲ组)和14尾/m~2(Ⅳ组),投喂粗蛋白含量为42%、粗脂肪22%的颗粒饲料,常规养殖。145d的养殖表明:网箱养殖的放养密度对硬头鳟的生长有一定影响。第Ⅳ组鱼的存活率显著低于其他3组(P0.05);放养密度为5~11尾/m~2时硬头鳟的生长与密度呈正相关,大于此密度范围则呈负相关。第Ⅲ组鱼的终末体质量、日增重、增重率、利润和利润率显著高于其余3组(P0.05);4个密度组硬头鳟的产量随放养密度增加而递增。本试验表明:网箱养殖硬头鳟的放养密度为11尾/m~2较适宜。     

蓝点马鲛网箱养殖试验报告

在国内首次进行了蓝点马鲛网箱养殖试验。对网箱结构,苗种兼捕,苗种放养,饵料投喂,鱼病防治等整套技术进行了研究。７２ｍ＾２网箱共养养成商品鱼１５５１尾,成活率５５％,平均尾重５８０ｇ,饵料系数７．２,单位面积产量１２．５ｋｇ／ｍ＾２。专家鉴定认为,本研究填补了国内空白,达国内领先水平。     

Mortalities caused by the crustacean isopod, Cirolana fluviatilis, in tropical, cage-cultured Asian seabass, Lates calcarifer: a case study from the southwest coast of India

Recurring mortalities inflicted by the cirolanid isopod Cirolana fluviatilis in the juveniles of the Asian seabass, Lates calcarifer , stocked in a cage farm in the Cochin backwaters, from November 2006 to May 2007, were investigated. Hatchery-reared fingerlings (size 8–12 cm) were cultured in floating cages and mortalities were observed after a rearing period of 1 month. The fish were found dead in the cages, with only the remnants of fish skeleton and all the flesh eaten away. Investigations revealed a very high abundance of isopods, identified as C. fluviatilis (Crustacea, Malacostraca, Isopoda and Ciroloanidae). During the first 2 months of stocking, 35% of the fingerlings died, and the cumulative mortality reached 45% in 6 months, considerably reducing the profits from the venture. Management measures for the control of the isopods are discussed. This is the first report on the isopod, C. fluviatilis , inflicting serious mortalities in a tropical cage-rearing system in the southwest coast of India.     

Growth, Survival, and Feed Conversion Rates of Hatchery-Reared Mutton Snapper Lutjanus analis Cultured in Floating Net Cages

Abstract.— The aquaculture performance of mutton snapper Lutjanus analis raised in floating net cages was assessed by measuring their growth, survival, and feed conversion rates during a growout trial conducted in a 3.2‐ha saltwater lake in the Florida Keys, Florida, USA. Approximately 10,500 hatchery‐reared finger‐lings were stocked in two circular, high‐density polyethylene (HDPE) net cages of 7‐m diameter × 7‐m deep (300 m²) and 10‐m diameter × 7‐m deep (600 m³) dimensions. Cages were stocked at 25 fish/m³ (3.2 kg/m³) and 5 fish/m³ (0.72 kg/m³), respectively. Fish grew from a mean of 16.5 g to 302.8 g (25.6 cm TL) in 246 days in the former cage and from a mean of 42.3 g to 245.6 g (23.8 cm TL) in 178 d in the latter cage. Growth rates in weight were best expressed by the following exponential equations: cage 1 (high stocking density): W = 20.716 e^0.0112x (r²= 0.83); cage 2 (low stocking density): W = 38.848 e^0.0118x (r²= 0.81). Length‐weight data indicate that hatcheryraised, cage‐cultured mutton snapper are heavier per unit length than their wild counterparts. There was no significant difference (P < 0.05) between the slopes of the two lines, indicating that fish in the two cages grew at the same rate. The length‐weight relationships for mutton snapper stocked in cages 1 and 2 are expressed, respectively, by the equations W = 0.000009 L ^3.11 (r²= 0.99) and W = 0.000005 L ^3.22 (r²= 0.97). Overall feed conversion rate for both cages combined was 1.4. Approximately 10% of the fish sampled exhibited some degree of deformity, particularly scoliosis. Overall survival rate was 70%. Results suggest that L. analis has potential for aquaculture development in net cage systems.     

Premiers resultats de l'elevage en cages de Tilapia nilotica (L.) dans le Lac Kossou,Cote d'IvoirePreliminary results of cage rearing Tilapia nilotica (L.) in Lake Kossou,Ivory Coast

The experimental rearing of T. nilotica in 1-m³ cages floating in Lake Kossou, Ivory Coast, was performed between March 1974 and April 1975. The fish were fed water-stable pellets (24.7% protein), the daily ration generally varying between 6 and 3.4% of the ichthyomass present. Fingerlings (9–55 g each) were stocked at densities of 200–400 fish/m³. They reached commercial size (more than 200 g) within 4–6 months, depending on the biomass present in the cage (stocking density and average individual weight of fish), as well as on limological conditions. The average annual mortality was 5.9%. Annual production varied from 36 to 64 kg/m³. The feed conversion rate averaged 2.8. A reduction of the daily ration for fish larger than 40 g reduced this value.Fingerlings should average at least 20–30 g in weight at initial stocking of the cage. Two crops a year can then be easily realized. If only male fish are reared, three harvests per year appear to be possible, increasing the annual cage production of fish close to 200 kg/m³ with proper management.The possible development of T. nilotica cage culture is actually hampered due to the lack of adequate fish feed available commercially, and to the lack of sufficient quantities of calibrated fingerlings throughout the year.     

Effect of Feeding Frequency, Water Temperature, and Stocking Density on the Growth of Tiger Puffer, Takifugu rubripes

Effects of daily feeding frequency, water temperature, and stocking density on the growth of tiger puffer, Takifugu rubripes, fry were examined to develop effective techniques to produce tiger puffer in a closed recirculation system. Fish of 4, 14, and 180 g in initial body weight were fed commercial pellet diets once to five times a day to apparent satiation each by hand for 8 or 12 wk at 20 C. Daily feeding frequency did not affect the growth of 14‐ and 180‐g‐size fish. However, the daily feed consumption and weight gain of the 4‐g‐size fish fed three and five times daily were significantly higher than those of fish fed once daily (P < 0.05). Fish of 4 and 50 g in initial body weight were reared with the pellet diet at 15–30 C for 8 wk. The weight gain of fish increased with increasing water temperature up to 25 C and decreased drastically at 30 C for both sizes. Similar trends were observed for feed efficiency, although 4‐g fish had highest efficiency at 20 C. Effects of stocking density on growth were examined with fish of 8, 13, and 100 g in initial body weight. Fish were reared with the pellet diet for 8 or 16 wk at 20 C. Fish were placed in floating net cages in the culture tank, and the stocking density was determined based on the total weight of fish and volume of the net cage. Fish of 8 g in body weight grew up to 35–36 g during the 8‐wk rearing period independent of the stocking density of 8, 15, and 31 kg/m³ at the end of rearing. Final biomass per cage reached 32, 60, and 115 kg/m³ for 13‐g‐size fish, and 10, 18, and 35 kg/m³ for 100‐g‐size fish, and the growth of the fish tended to decrease with increasing stocking density for both sizes.     

Effects of night‐time light intensity on the survival rate and stress responses in juvenile Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel)

Land‐based cultured juvenile Pacific bluefin tuna Thunnus orientalis (PBT) have high mortality rates due to collisions or contacts with tank walls after about 30 days of hatching. To determine the effect of night‐time lighting on their survival, juvenile PBT were reared under four different night‐time light intensities (0, 5, 15 and 150 lx) for 9 days, followed by a 3‐day observation period. High‐intensity, night‐time lighting (150 lx) significantly improved the survival rate (75.8%; P < 0.001) compared with the unlit control group (0 lx, 64.3%). The survival rate in the high‐intensity group decreased after the end of the lighting period. Lighting did not influence whole‐body cortisol levels, glucose levels, or diel changes in plasma cortisol levels. In contrast, the survival rates of fish exposed to light intensities between 5 and 15 lx were slightly lower than that of the unlit control group. These results suggest that providing night‐time lighting of 150 lx or higher is an effective method for reducing the mortality of cultured PBT.     

Mortality patterns in infectious salmon anaemia virus outbreaks in New Brunswick, Canada

Mortality levels attributed to infectious salmon anaemia viral (ISAV) infections were examined at the net pen and site level in the 1996 smolt year class in three areas of New Brunswick, Canada. The year class in this region was the first known to have potential exposure to ISAV beginning at the time of seawater transfer. There was considerable variability in mortality patterns among net pen groups of fish. Net pen outbreak definitions were based on at least seven high mortality days in which there were at least 100 per 100 000 fish per day or >5% cumulative mortality for the study period. There were 106 net pen outbreaks in a study population consisting of 218 net pens. Although the number of new cases decreased as water temperature decreased, overall mortality levels at the study sites did not decrease noticeably. The median peak daily mortality rate during outbreaks was 492 per 100 000 fish per day, with 10% of cases experiencing >5200 mortalities per 100 000 fish per day. The median duration of outbreaks in net pens for which the fish were not slaughtered during the outbreak was 33 days and the median total loss in those outbreaks was 6600 per 100 000 fish.     

池塘网箱养鱼的可行性及技术研究

１９９５、１９９６年在精养成鱼塘设置网箱养殖商品湘鲫与乌鳢鱼种，采取灌排水形成微流、启动增氧机、投放耐低氧吃食性鱼类、投喂颗粒馈料和动物肉、勤刷钢箱养措施，结果：湘鲫养殖１３６天，从１５０ｇ长到６７０ｇ，平均日增重３．８２ｇ，２５ｍ＾２的网箱产成鱼３３４．３３ｋｇ。平均１３．３ｋｇ／ｍ＾２，成活率９９．８％，乌鳢种培育４２天，由体长１ｃｍ到１０ｃｍ，平均日增长２．１４ｍｍ，２０ｍ＾２的网箱，共育鱼