Effect of water surface condition on survival,growth and swim bladder inflation of yellowfin tuna,Thunnus albacares (Temminck and Schlegel), larvae

Early‐stage mortality due to surface water tension‐related death and due to sinking to the tank bottom was investigated for yellowfin tuna, Thunnus albacares (YFT), larvae. Different aeration rates and rearing water surface conditions were examined to evaluate the effect on larval survival, swim bladder inflation and growth. The percentage survival of yolk sac larvae was significantly higher when the rearing water surface was covered with fish oil at aeration rates of 0 and 50 mL min^?1. The highest mortality occurred at the highest aeration rate of 250 mL min^?1 regardless of surface water condition. A second experiment was conducted twice under different water surface conditions: the water surface was covered by fish oil (FO), skimmed of fish oil (SS), and was not treated (NC). The percentage survival was not significantly different between treatments after 7 days of feeding. In contrast to the survival, the proportion of larvae with inflated swim bladders was significantly higher for the NC and SS groups than that of the FO group. Results of these experiments indicate that the addition of oil to the rearing water surface without its removal interferes with the initial swim bladder inflation in YFT larvae. These results also indicate that YFT larvae need to obtain (gulp) air at the water surface for initial swim bladder inflation, and success of initial swim bladder inflation may be crucial for their survival.     

Initial swim bladder inflation in the larvae of Tilapia mossambica (Peters) and Morone saxatilis (Walbaum)

Tilapia and striped bass larvae inflate their swim bladders on the 7th–9th and 5th–7th days after hatching, respectively. The primordial bladder of Tilapia has no pneumatic duct and larvae do not gulp atmospheric gas for the initial swim bladder inflation. Prominent columnar epithelium is characteristics of the bladder of Tilapia prior to inflation. Hypoxic conditions inhibit inflation and result in degeneration of the columnar epithelium and the irreversible malfunction of the swim bladder. The swim bladder of the striped bass has a glandular epithelium and a pneumatic duct prior to inflation. The mode of the initial inflation and functional role of the pneumatic duct remain unclear, although strong aeration and turbulent water in the rearing containers were observed to be main factors enhancing normal inflation of the larval swim bladder.     

Influence of initial swimbladder inflation failure on survival of Pacific bluefin tuna,Thunnus orientalis (Temminck and Schlegel), larvae

This study investigated the influence of initial swimbladder inflation (ISI) failure on survival of Pacific bluefin tuna (PBT), Thunnus orientalis, larvae to prevent mass mortality due to sinking death. In Experiment 1, swimbladder inflation frequency and survival within an ISI promoted (PS) group, for which surface film of rearing water was removed, and a group without ISI promotion (NPS) were compared in 20 and 30 kL tanks. The PS group demonstrated significantly higher swimbladder inflation frequency and increased survival than the NPS group within 20 kL tanks at 9 days post hatching (dph). Similar tendencies were observed within 30 kL tanks. In Experiment 2, larval distribution and swimbladder inflation frequency in the night‐time were examined through larval sampling within the upper and middle layers of the water column and tank bottom within 1.6 and 30 kL tanks at 5 dph. Larvae at tank bottom had higher distributional density and significantly lower swimbladder inflation frequency than those distributed in the upper and middle layers within 1.6 kL tanks. Similar tendencies were observed within 30 kL tanks. Results of this study suggest the improvement of larval survival due to prevention of sinking death through ISI promotion in mass‐scale PBT larviculture.     

Swim bladder inflation as a possible cause of saddleback-like syndrome malformation in hatchery-reared red spotted grouper <Emphasis Type="Italic">Epinephelus akaara</Emphasis>

Saddleback-like syndrome is one of the most frequently observed malformations in hatchery-reared red spotted grouper Epinephelus akaara. Saddleback-like syndrome is characterized by a V-shaped dorsal-profile depression behind the head region accompanied by deformities or misalignments of the first to fourth neural spines on the vertebral column and the first to fourth pterygiophores of the dorsal fin. Abnormal swim bladder inflation in several finfish species leads to malformations, particularly of the vertebral column. The present study examined the influence of swim bladder inflation on saddleback-like syndrome in hatchery-reared red spotted grouper. The incidence of saddleback-like syndrome increased as swim bladder inflation rate increased. Additionally, the incidence of saddleback-like syndrome among juveniles with inflated swim bladders was significantly higher than that among juveniles with uninflated swim bladders. The larval swim bladder is located just below the first to fifth vertebrae and the first to fifth dorsal spines, where saddleback-like syndrome occurs. Our results suggest that an inflated swim bladder increases the risk of saddleback-like syndrome in hatchery-reared red spotted grouper.     

Promotion of initial swimbladder inflation in Pacific bluefin tuna,Thunnus orientalis (Temminck and Schlegel), larvae

Initial swimbladder inflation (ISI) of Pacific bluefin tuna (PBT), Thunnus orientalis, larvae was studied to increase the survival of cultured larvae. Experiment 1 was conducted to explore promotion and inhibition of ISI under different water surface conditions; including the use of surface skimmer to remove autogenous surface substances (SS), covering the water surface with liquid‐paraffin‐layer (LP) and oil film (OF), and a control (non‐treatment, NT). Significantly higher inflation frequency was observed in SS (62.2%) than NT (11.9%), LP (2.7%) and OF (3.9%). This indicates that ISI in PBT larvae can be promoted by removal of surface substances on rearing water which inhibit larval air gulping. Experiment 2 aimed to elucidate proper day of larval age to start skimming for promoting ISI with four different periods of oil film removal: from 3 to 8 (SF3D), 4 to 8 (SF4D), 5 to 8 (SF5D), 6 to 8 (SF6D) days‐post‐hatch (dph). Significant improvement in ISI frequency was observed in SF3D (80.2%) but the frequency was very poor in SF4D, SF5D, and SF6D (17.8–7.5%). This implies the need of oil film removal without missing a narrow window, 1 day of 3 dph, to promote ISI in practical PBT larviculture.     

The effects of cadmium and copper on embryonic and larval development of ide Leuciscus idus L.

The effects of Cd and Cu on embryos and larvae of the ide Leuciscus idus were evaluated. The ide is an European cyprinid fish, natural populations of which tend to decrease. The ide is also used as a bioindicator organism to evaluate water quality. However, sensitivity of ide early developmental stages to heavy metal intoxication is not known. Fish were exposed to Cd or Cu (100 μg/L) during embryonic, larval or both developmental periods. Survival of the embryos, time of hatching, size and quality of newly hatched larvae were evaluated at the end of embryonic period. Correctly developed larvae from the control and Cd or Cu-exposed groups were transferred to clean water, Cd or Cu solutions (100 μg/L) immediately after hatching. Larval development was observed, and the larvae were photographed. Time of yolk sac resorption, onset of active feeding and swim bladder inflation were evaluated, and the measurements were done on body and swim bladder size. The results showed that exposure of embryos to Cd and Cu significantly reduced embryonic survival and increased frequency of body malformations and death in newly hatched larvae and delayed hatching. Exposure to Cd and Cu during larval period reduced larval survival, growth and delayed development (yolk utilization, beginning of active feeding and swim bladder inflation). Cadmium was more toxic to the ide embryos and larvae than copper. Exposures to metals during embryonic period alone caused adverse impact on larval performance even when larval development took place in clean water. However, exposure of embryos to Cu reduced toxic impact of metal on larvae in continuous Cu exposure compared to the non-preexposed fish, but no such an effect occurred in case of Cd exposure. The results show that even a short-term exposure to Cd or Cu during early development of ide may adversely affect recruitment of this species. Among the measured endpoints, quality of newly hatched larvae (frequency of body malformations and larvae dead immediately after hatching) and swim bladder size were the most sensitive to intoxication with both metals. Embryos were more sensitive to Cu intoxication than larvae, while in case of Cd, sensitivity of both stages was similar.     

Swim bladder inflation and survival of Mugil cephalus to 50 days

Excessive inflation of the swim bladder causes immobility and mortality of 12-day old larvae of Mugil cephalus and other marine fish. Increased aeration or mechanical agitation of the water in rearing tanks maintained the larvae below the water surface, and the swim bladder formed and functioned normally. Survival was dramatically increased. Two experimental production tanks, stocked initially with 15 000 and 20 000 larvae, at a density of 5.25 and 7.0/l, respectively, yielded 33.5% and 16.9% juveniles on day 50. Only an outbreak of ciliated parasites prevented both tanks from having survival figures of over 30%.     

Dynamics of yolk sac and oil droplet utilization and behavioural aspects of swim bladder inflation in burbot, Lota lota L., larvae during the first days of life, under laboratory conditions

The study concerns investigation of early larval development of burbot, Lota lota. As part of a two-year study, the first 15 days (until the end of yolk sac resorption) of burbot larvae development under controlled conditions were examined. The aim of the study was to observe the moment of swim bladder inflation and the behavioural aspects of this process, as well as the analysis of yolk and oil droplet resorption and the beginning of exogenous nutrition. It was observed that larvae began to inflate their swim bladder on the 3rd day post-hatch. On 5 DPH, none of the larvae without an inflated bladder was able to swim up the distance separating it (10 cm) from the water surface. Since 9 DPH, 50 % of larvae started exogenous feeding, and the absence of yolk was observed on 13 DPH and oil droplet on 14 DPH, while on 15 DPH, 100 % of feeding larvae were observed. The presented results indicate that the analyzed period is critical for burbot, and it is characterized by a high mortality rate (over 60 %). Additionally, the results suggest that, under controlled conditions, the latest moment when burbot larvae should be given exogenous food is 9–10 DPH and until the moment of the swim bladder inflation, larvae should be kept in tanks with a low water depth (up to 10 cm). The data presented in this study could have a significant influence on the efficiency of larvae rearing, both for aquaculture and for restocking purposes.     

The role of phototaxis in the initial swim bladder inflation of larval yellow perch ( Perca flavescens )

The yellow perch (Perca flavescens) is a high priority species for aquaculture, with strong demand in the USA. Unfortunately, numerous developmental problems during larval rearing prevent its commercial viability. Failed swim bladder inflation (SBI) has been reported in the culture of numerous physoclistous fish species and is a prominent problem in the culture of yellow perch. Initial SBI occurs within a short period of ontogeny, and missing this opportunity results in permanent malformation of the organ. Lighting cues appear to play a role in triggering the response of rising to the surface to swallow the air required for initial SBI in several fishes including yellow perch. Larval yellow perch are photopositive, and this phototactic response seems to co-occur with the window of opportunity for SBI. Thus, we examined the role of phototactic behavior and low-intensity, moonlight-like illumination in initial SBI in yellow perch. Lights were positioned below and above the water surface in larval culture tanks to see if the presence of nighttime illumination impacted SBI success, and if the phototactic behavior of yellow perch helps them find the water surface when inflating at night. The results of this study reveal that even very low-intensity nighttime light reduces the proportion of yellow perch larvae to initially inflate regardless of the direction of the light source. Also, on treatment with no nighttime illumination, higher than expected SBI was observed, and the culture conditions that produced this success should be examined when focusing on improving SBI in the future. This research suggests that the photopositive response of yellow perch is not involved in SBI success, and lighting could play a role in hindering the process.     

Effects of docosahexaenoic acid on growth,survival and swim bladder inflation of larval amberjack ( Seriola dumerili, Risso)

The effect of docosahexaenoic acid (DHA) on the growth performance, survival and swim bladder inflation of larval Seriola dumerili during the rotifer feeding period was investigated in two feeding experiments. Amberjack larvae at 3 day post hatching were fed rotifers enriched with (1) freshwater C hlorella (Chlo), (2) a mixture (2:1, v/v) of Chlo and DHA‐enriched C hlorella (DHA‐Chlo), (3) DHA‐Chlo and (4) DHA‐Chlo and commercial DHA emulsion, in triplicate for 7 days. The average DHA contents of the rotifers were 0.0, 0.4, 1.0 and 1.9 mg g^?1 DM respectively. The survival rate was improved by the enrichment of rotifers with DHA‐Chlo alone, and DHA‐Chlo and emulsion. Growth and swim bladder inflation of fish fed rotifers enriched with DHA‐Chlo were significantly (P < 0.05) improved, however, with increased levels of DHA further improvement was not found. DHA content in the larval whole body proportionally increased with the DHA level in the rotifers. These results suggest that DHA enrichment of rotifers is effective to improve the growth, survival rate and swim bladder inflation of amberjack larvae. The DHA requirement of amberjack larvae is estimated to be 1.5 mg g^?1 on a dry matter basis of rotifers.     

Lordotic Deformation and Abnormal Development of Swim Bladders in Some Hatchery-Bred Marine Physoclistous Fish in Japan

At many hatcheries in Japan, a high incidence of lordosis is being reported among marine physoclistous juveniles of red sea bream, Japanese sea bass, and amberjack. Extensive studies being conducted since 1975 to tackle this problem have led to the following conclusions, and effective countermeasures are being proposed.
During early larval development in the temporary physostomous stage, fish must be able to gulp air at the water surface for normal development of the swim bladder. The juveniles that fail to gulp air swim upward in an oblique position because of insufficient buoyancy, causing the backbone to curve in a V-shape.
The managerial solutions proposed are: 1) reduce the strong water current caused by vigorous aeration; 2) provide nutrient-enriched rotifers to produce healthy swimming larvae; and 3) prevent any oily film formation on the water surface.     

Diel and ontogenetic body density change in Pacific bluefin tuna, Thunnus orientalis (Temminck and Schlegel), larvae

Diel and ontogenetic changes in larval body density related to swim bladder volume were investigated in Pacific bluefin tuna, Thunnus orientalis, to determine the causality of larval mortality – adhesion to the water surface and contact with the tank bottom during seedling production. The density of larvae with deflated swim bladders increased with total length and days post hatch. Diel density change was observed after day 2 post hatch; owing to daytime deflation and night‐time inflation of the swim bladder, the density was relatively higher during the daytime. Increased swim bladder volumes clearly reduced larval density during the night‐time after day 9 post hatch. However, the density of larvae with inflated swim bladders was greater than rearing water density (Δρ>0.0099). The small density difference between larvae and rearing water (Δρ=0.0022?0.0100) until day 4 post hatch may have caused larval mortality by adhesion to the water surface because larvae can be easily transported to the water surface by aeration‐driven upwelling in rearing tanks. Density increased noticeably from day 5 to day 9 post hatch. The increased density difference (Δρ=0.0065?0.0209) in larvae and rearing water possibly induced mortality by contact with the tank bottom because larvae sink particularly during the night‐time on ceasing swimming.     

Analysis of sinking death using video images of the swimming performance of Pacific Bluefin tuna (Thunnus orientalis) larvae

In this study, we aimed to clarify the mechanism of sinking death during the larval stage of Pacific Bluefin tuna Thunnus orientalis by investigating the effects of swimming performance on sinking death, using a behavioral approach. Swimming performance was examined 3–9 days after hatching (DAH) under day and night light conditions in cuboid experimental tanks. Swimming behavior variables such as swimming speed and swimming angle were measured under both light conditions. Larvae in the daytime experiment and larvae with inflated swim bladders at night were distributed on the surface layer of the water column. In contrast, larvae with uninflated swim bladders at night were frequently observed swimming vertically or sinking to the bottom of the tank. Larvae with inflated swim bladders at night were always distributed beneath the surface until the next morning (survival rates were 100 %). However, larvae with uninflated swim bladders at night swam upward repeatedly and later sank to the bottom of the tank (survival rates were 60 % and 38 % at 5 and 9 DAH, respectively). Larvae with uninflated swim bladders were not always able to maintain their swimming depth by swimming until the next morning. Additionally, their swimming speed and vertical swimming frequency (ratio) depended on the illumination and swim bladder conditions. Our findings show that larvae with uninflated swim bladders at night were associated with a higher risk of sinking death. The swimming energy capacity of Pacific Bluefin tuna larvae, which indicates the total amount of the energy that enables individuals to swim throughout the night without feeding, was found to be linked to sinking death.     

Effect of different algae used for enrichment of rotifers on growth, survival, and swim bladder inflation of larval amberjack Seriola dumerili

The effect of algae with different DHA contents used for the enrichment of rotifers on the growth performance, survival, and swim bladder inflation of larval amberjack Seriola dumerili was investigated. Rotifers were enriched with freshwater Chlorella vulgaris containing three levels of DHA (rotifer containing DHA 0.04, 0.60, 1.32?g DHA 100?g^?1 DM) and Nannochloropsis (0.04?g DHA 100?g^?1 DM; 2.54?g EPA 100?g^?1DM). The larvae were fed the enriched rotifers in triplicate from 3?days post-hatch for 7?days in static condition. The same algae used for rotifer enrichment were supplied to the larval tanks. Growth and survival rate of fish fed the rotifers enriched with Nannochloropsis were higher than those of fish fed the rotifers enriched with all three Chlorella treatments. Swim bladder inflation was lowest in fish fed the rotifers enriched with Nannochloropsis. The proportion of EPA was higher in fish fed the rotifers enriched with Nannochloropsis, while that of DHA increased proportionally with the DHA levels in the rotifers enriched with Chlorella. These results suggest that rotifers enriched with Nannochloropsis (EPA-rich rotifers) are effective to enhance growth and survival, but DHA instead of EPA is essential to improve the swim bladder inflation in amberjack larvae.     

Characterization of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare (Schultz), and the effect of exposure to methylene blue

Failure to inflate the swim bladder is regarded a major obstacle in the rearing of many fish species. We present a study of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare. A normal developing primordial swim bladder was first discernable at the end of the first day post-hatch (p.h.) as a cluster of epithelial cells with a central lumen, surrounded by presumably mesenchymal cells. Initial inflation occurred on the fourth day p.h. Prior to inflation the swim bladder epithelium consisted of an outer squamous and inner columnar layer. Cells of the inner layer were filled at their basal region with an amorphous material, which disappeared upon inflation. A pneumatic duct was absent, and larvae presented no need to reach the water surface for inflation, suggesting that angelfish are pure physoclists. A model for the role of the amorphous material in normal initial inflation is proposed. Abnormal swim bladders were apparent from the fourth day p.h., and methylene blue (MB) at a concentration of 5 ppm significantly increased the prevalence of SBN. Histologically, abnormal swim bladders in larvae hatched in 5 ppm MB could not be distinguished from those in fish raised under routine conditions (0.5 ppm MB). We suggest that MB may have a teratogenic effect in angelfish.     

鳔器官的发育对人工培育鱼苗的影响

论述了鳔器官的发育对海水鱼类人工培育苗种的影响，仔鱼期鳔的形成和充气是影响闭鳔海水鱼类人工育苗成效的重要因素之一，鳔发育异常一是导致仔稚鱼死亡，二是导致脊柱前凸。在人工养殖条件下，影响海洋闭鳔鱼类鳔器官充气的因子有营养因子和环境因子，充气量，水表面的油膜，温度，盐度和光照等环境因子影响仔鱼水表面吞饮空气，影响鳔的充气率，仔鱼摄食EPA和DHA含量低的饵料后，活力差，仔鱼到达水表面吞饮空气的能力下降，鳔的开腔率降低，此外仔鱼体内甲状腺素的含量可能对仔鱼鳔的开腔率产生影响。     

Combined Effects of Diet and Salinity on European Sea Bass Larvae Dicentrarchus labrax

Effects of diet, salinity, and consumption of endogenous reserves on the growth, survival and swim bladder inflation of European sea-bass larvae were studied. Primary inflation of the swim bladder occurs in 7-day-old larvae. Inflation is synchronized with the absorption of endogenous reserves. The kinetics of the consumption of these reserves varies with the diets tested, and is the slowest at higher salinity (28.7 and 37.7‰). Best results were obtained with larvae fed on Artemia nauplii. Larvae raised at lower salinity (19.7 and 10.7‰) had the highest proportion of inflated swim bladders. Larvae raised at 28.7‰ salinity had the best survival rate, while those raised at 38.7‰ had the best growth rate. Larval mortality was associated with inappropriate functioning of the swim bladder. Larvae exposed to decreasing salinity during rearing showed very high survival rates and normal swim bladder inflation.     

Embryonic and larval development of serpae tetra Hyphessobrycon eques (Steindachner, 1882)

In this study, the embryonic and larval development stages of one of the most important ornamental fish serpae tetra (Hyphessobrycon eques) are described. The early life stage is documented from fertilization until the beginning of the juvenile period. The fertilized eggs (the average diameter = 938.55 ± 35.20 µm) were incubated at a water temperature of 26 ± 0.5°C. The cleavage finished in 1:10 hr (=h) and the early blastula stage occurred at 1:26 hr post fertilization (hpf). The gastrulation started at 3:05 hpf, and 50% epiboly was observed at 3:25 hpf. Segmentation stage was monitored at 7:26 hpf. Embryonic developmental stage was completed and hatching occurred 20–21 hpf. The total length (TL) of newly hatched larvae was 2.64 ± 0.21 mm. The larval development of serpae tetra was divided into four different periods: Yolk‐sac larva (1–4 DAH, TL = 2.77 ± 0.09 mm ‐ 3.85 ± 0.11 mm), preflexion larva (5–12 DAH), flexion larva (13–15 DAH, TL = 5.78 ± 0.46 mm on the 15th day) and post‐flexion larva (16–30 DAH, TL = 10.7 ± 0.27 mm on the 28th–30th days). The mouth and anus are closed at 1 DAH. The mouth and anus opened at 4 DAH. Exogenous feeding started on the 4th day. The first gulping of the swim bladder was on days 3. The larva begins to swim freely, and the yolk sac was completely consumed at 4 DAH. Histological structures of the eye and brain of new hatched larva were clearly identified at 1 day after hatching (DAH). According to histological findings, the digestive system (stomach, intestine) started to develop and the liver could be seen on the ventral side of the swim bladder at 5 DAH. No histological difference was observed between the anterior intestine and the posterior intestine at 15–16 DAH. The larval metamorphosis was completed, and the larvae transformed into juveniles at 28–30 DAH.     

Effect of water temperature and light intensity on swim bladder inflation and growth of red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis> larvae

This study aimed to examine the effect of different water temperatures and light intensities on swim bladder inflation (SBI) and growth of red sea bream Pagrus major larvae to improve rearing techniques for this species. Two sets of experiments were conducted: different rearing temperatures were used in experiment 1 (19, 21, 23, and 25 °C), and different light intensities in experiment 2 (250, 1000, 4000, and 16,000 lx). Water temperature did not affect SBI frequency, but SBI initiation was accelerated at higher temperature, i.e., it was initiated on 3 days post-hatching (dph) at 25 °C and on 6 dph at 19 °C, suggesting that the promotion period for SBI, which needs a surface skimmer to be  run, also accelerated with increasing temperature in red sea bream larviculture. A higher temperature also significantly promoted larval growth, although the notochord of larvae at SBI initiation was shorter at higher temperatures. Light intensity had no effect on either the initiation or the frequency of SBI. However, light intensity of 250 lx significantly reduced early larval growth compared to light intensities higher than 1000 lx. These results indicate that light at an intensity greater than 1000 lx at the water surface is suitable for the early larviculture of red sea bream.     

The pseudo-green water technique for intensive rearing of sea bream (Sparus aurata) larvae

The “pseudo green water” technology for sea bream(Sparus aurata) larval rearing was evaluated by analyzingresults of a 2-year study, performed in a pilot scale system. Thetechnology is characterized by the daily addition of phytoplankton in therearing tanks during the first month of rearing. Effects of egg origin,spawningseason and initial larval density on the larval rearing were investigated. Fishreared in “pseudo green water” systems for 60 days, presented highbiological performance in terms of survival (56 ± 16%), meanweight (62 ± 12 mg), total length (20 ± 1mm), conformity with wild standard (88 ± 9%), andfunctional swim bladder (93 ± 4%). The results present homogenitybetween the categories (origin of eggs, time of spawning, initial egg density)studied, proving the stability of the technology.