Positive phototaxis as the cause of jaw malformations in larval greater amberjack,Seriola dumerili (Risso, 1810): Mitigation by rearing in tanks with low‐brightness walls

Jaw malformations are a serious problem in fingerlings of the greater amberjack, Seriola dumerili. To establish a countermeasure against these malformations, we conducted a larval behavioural test to identify their root cause, and we investigated the ability of low‐brightness rearing tank walls to control their occurrence. Larval distribution was examined in a horizontally illuminated rectangular transparent aquarium (20 cm × 100 cm × 25 cm), and their distribution was biased towards the light source after this lighting was provided from 3 to 13 days post hatching (dph), indicating positive phototaxis; this response disappeared on 22 dph (there are no data between 13 and 22 dph). Larvae were observed to swim phototactically towards the light source and repeatedly collided with the tank wall (walling behaviour). To investigate the ability of wall brightness to control the incidence of jaw malformations, we compared their incidence in a rearing trial with different Munsell colour values for the tank walls: 2.11 (black), 5.85 (grey) and 9.52 (white). The incidence rate of jaw malformations at 25 dph was significantly lower in the tanks with lower‐brightness walls, that is, 5.8%, 22.5% and 26.8% for black, grey and white respectively. Larval walling behaviour was most intense for white, followed in order by grey and black. These results indicate that positive phototaxis elicits larval walling behaviour, causing jaw malformations, and that low‐brightness tank walls control this 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.     

Multiple GnRHa injections to induce successful spawning of wild caught greater amberjack (Seriola dumerili) matured in captivity

Reliable reproduction and sufficient amounts of juveniles obtained in captivity constitute a main bottleneck for mass production of greater amberjack. The aim of the present study was to combine several aspects of broodstock management and hormonal induction, to obtain a large number of high quality spawns. Captured Seriola dumerili sub‐adults were kept for three years in 10 m³ tanks. When fish were larger than 75 cm, they were individually tagged, periodically explored to determine gonad maturation and injected with gonadotropin releasing hormone analogue from June to October. A total of 15 inductions to four males and two females produced 330 821 ± 219 519 eggs/induction and a total of 22 spawns. The number of spawns and female fecundity (2.48 millions eggs/female/spawning season) were similar to those of free wild populations and higher than those previously obtained in captivity for this species. Egg quality increased from an initial low in the first two spawns in June to give, during July to October, a mean of 96.01 ± 6.50% fertilized eggs, 92.58 ± 17.56% hatched eggs, 78.66 ± 12.60% larval survival at day 3 after. These results showed that intramuscular injections of 20 μg kg^?1 body weight GnRHa under natural temperature and photoperiod conditions in the Canary Islands produced a high induction efficiency.     

Effect of different rearing conditions on body lipid composition of greater amberjack broodstock (Seriola dumerili)

The aim of this study was to assess the effect of two rearing conditions: outdoor environment with great volume tanks (500 m³) and low stocking density (~0.4 kg m^?3); and indoor environment with smaller volume tanks (10 m³) and higher stocking density (~5 kg m^?3), on muscle, liver and ovary lipid composition of Seriola dumerili broodstock born in captivity. The rearing conditions tested seem to affect the pattern of lipid body deposition in broodstock fish of S. dumerili, increasing the muscle and liver triacylglycerides (TG) accumulation of fish kept under indoor conditions, probably due to reduced energy expenditure in swimming, with some variations in the fatty acid profile that may respond to the differences in the culture conditions tested. No significant differences were found for Gonadosomatic Index (GSI) or ovary lipid deposition between groups in this study, which may suggest that the conditions tested do not have a major effect on ovary development. However, one season later the females kept under outdoor conditions released eggs spontaneously, whereas those kept under indoor conditions did not spawn, suggesting that the conditions tested actually have an effect on the broodstock's reproductive fitness. More studies are needed in order to evaluate whether the conditions tested have or not any influence on ovary development.     

Encephalomyelitis associated with microsporidian infection in farmed greater amberjack, Seriola dumerili (Risso)

An outbreak of a disease characterized by a peculiar spiral movement in farmed greater amberjack, Seriola dumerili (Risso), occurred in Kagoshima Prefecture, Japan, in May 2008, immediately after importing the fish from China. Although neither bacteria nor viruses were detected in routine diagnostic tests, histopathological observations of the affected fish revealed severe inflammation in the tegmentum of the brain including the medulla oblongata and the anterior part of the spinal cord. In addition, a microsporidian parasite was observed in the nerve cell bodies or axons in the inflamed tissues. We identified a microsporidian small subunit rRNA gene (SSU rDNA) from the lesion, and the sequence showed 96.1% identity with that of Spraguea lophii. Subsequent in situ hybridization using probes presumably specific to the SSU rRNA confirmed that the parasite observed in histopathology harboured the identified SSU rRNA. Apparently degenerated microsporidian cells or spores were also frequently observed in tissue sections. Thus, the disease was most probably caused by the infection of a hitherto unknown microsporidian parasite that has a genetic affinity to the genus Spraguea, in the central nervous system of the amberjack.     

Increased melanomacrophage centres in the liver of reproductively dysfunctional female greater amberjack Seriola dumerili (Risso, 1810)

The greater amberjack Seriola dumerili is a new aquaculture fish that may display reproductive dysfunctions. During extensive follicular atresia, which is a common reproductive dysfunction in females during vitellogenesis, part of the reabsorbed yolk returns to the liver to be metabolized and recycled. Melanomacrophage centres (MMCs) are aggregates of macrophage-like cells that play a role in the destruction, detoxification and recycling of endogenous and exogenous materials, and have been associated with systemic stress. Wild and captive-reared greater amberjack were sampled in the Mediterranean Sea during two different phases of the reproductive cycle. The liver of reproductively dysfunctional captive-reared females sampled during the spawning season showed a high density of both MMCs and apoptotic cells. A weak liver anti-cytochrome P450 monooxygenase 1A immunoreactivity was observed, suggesting that the examined fish were not exposed to environmental pollutants. We propose that the observed increase in MMCs and apoptosis in captive-reared fish was related to the hepatic overload associated to the metabolism of yolk proteins reabsorbed during extensive follicular atresia. Since follicular atresia is a frequent physiological and pathological event in teleosts, we suggest that the reproductive state should be always assessed when MMCs are used as markers of exposure to stress or pollutants.     

Effect of fish oil replacement and probiotic addition on growth,body composition and histological parameters of yellowtail (Seriola dumerili)

Fish (175 g of initial weight) were fed in triplicated groups with four diets formulated by 0% (FO 100), 75% (FO 25) and 100% (with and without probiotics, FO 0 and FO 0+) of fish oil replacement consisting of a mixture of linseed, sunflower and palm oils. After 109 days, growth and nutritional parameters were not affected by the treatment; however, fish fed with 0% of fish oil showed the lowest survival rate and without differences between the same diet with probiotics. As for biometric parameters, significant differences in the viscerosomatic index (VSI) were observed between fish fed the FO 0+ diet and the FO 100 and FO 25 diets. Results obtained from histological analysis did not detect inflammation in gut samples, while liver samples showed a remarkable steatosis in all four treatments. Total fish oil replacement produced a significant difference in the width of the lamina propria. The dietary inclusion of probiotics in the FO 0+ diet seems to favour a recovery of intestine histology. In addition, as fish oil substitution increased, the width of the lamina propria also increased. In conclusion, it is possible to affirm that the four diets administrated to Seriola dumerili did not compromise the correct development of the animals.     

Visualization of musculature of the larval greater amberjack Seriola dumerili (Risso) using whole‐mount immunostaining with special reference to cranial muscles

Muscles play important roles in feeding, respiration and swimming during not only adult stage but also larval stage in fish. However, there is no information of the muscle development in larval greater amberjack, Seriola dumerili (Risso). Here, we investigated muscle development in the greater amberjack, focusing primarily on the cranial muscles from 0 days post hatch (dph) to 12 dph using a modified whole‐mount immunohistochemical staining method. We found that the muscles required for feeding develop by 3 dph, when the larvae begin to feed. Subsequently, muscle composition in the dorsal branchial arches changes to the adult form between 5 and 8 dph. At 8 dph, all the muscles required for feeding and respiration appear, whereas the dorsal, pelvic and caudal fin muscles required for swimming develop later. This report provides fundamental information on larval greater amberjack muscle development, which will enable the detection of abnormal larval muscles and improve larval rearing techniques by modifying environmental conditions.     

Induction of spawning in Pacific white shrimp Litopenaeus vannamei (Boone, 1931) by injection of its molt inhibiting hormone isoform II produced in E. coli

The optimization of reproductive parameters in shrimp farming continues to be a challenge for most producing countries. Although the crustacean neuropeptides have been studied extensively in the last two decades, the functions of most of these neuropeptides remained putative. Among them, molt‐inhibiting hormone isoform II (MIH II) has shown an important role in vitellogenesis. In this study, the cDNA encoding mature MIH II peptide was isolated by RT‐PCR from the L. vannamei eyestalk. The cDNA was cloned into pET28a bacterial expression vector. Recombinant MIH II was obtained in the form of insoluble inclusion bodies and purified to ~88% purity. Two doses of rMIH II and a negative control group were assayed in vivo. The stages of ovarian maturation and spawning were recorded during 72 hr post‐injection. The results showed that ovarian maturation occurred approximately in 9% and 33% of females injected with rMIH II at the doses of 300 and 600 ng/gbw respectively. Neither maturation nor spawning was detected in the negative control group. Females injected with 600 ng/gbw, which showed vitellogenic stages III and IV, spawned. These preliminary results argue that the hormone rMIH II could be a promising candidate to induce spawning in L. vannamei shrimp.     

Assessment and comparison of proximate,fatty acid and mineral composition of six edible portions of South African cultured yellowtail (Seriola lalandi)

A whole fillet (A) and five distinct anatomical portions within a fillet (B–F) of South African farmed yellowtail were assessed for proximate, fatty acid and mineral composition. Within the whole fillet, moisture, protein, fat and ash accounted for 71%, 21%, 5% and 1% of the proximate composition respectively. Considerable inter‐muscular variation in nutritional composition was observed, however, the dorsal section (portions B and D) was most representative of the proximate, fatty acid and mineral composition of the whole yellowtail fillet and may be used in future studies. High variability in mineral and essential fatty acid content was observed and no one portion could be considered to contain a superior nutrient complex. South African farmed yellowtail can be considered a semi‐oily fish (5.3% fat) with relatively high levels of PUFA detected (PUFA > SFA > MUFA) primarily located in the dorsal and caudal sections. This study provided important information regarding the nutritional composition of South African reared yellowtail as well as recommendations regarding the sub‐sampling of specific portions for future nutrient composition studies.     

Effects of dietary n‐3 to n‐6 fatty acid ratios on spawning performance and larval quality in tongue sole Cynoglossus semilaevis

This study investigated the effect of n‐3 to n‐6 fatty acid ratios in broodstock diets on reproduction performance, fatty acid composition of eggs and gonads of tongue sole Cynoglossus semilaevis. Broodstock were fed five isonitrogenous and isoenergetic diets for 60 days. The supplemented lipids were prepared by a combination of fish oil and soybean oil inclusion FO (fish oil); FSO1 (fish oil: soybean oil = 7:1); FSO2 (fish oil: soybean oil = 2.2:1); FSO3 (fish oil: soybean oil = 1:1); FSO4 (fish oil: soybean oil = 1:4.3) as lipid sources with different n‐3 to n‐6 fatty acid ratios 10.40, 5.21, 2.81, 1.71 and 0.87. Results showed that relative fecundity, fertilization rate and survival rate of larvae at 7 days posthatching were all higher in broodstock fed FSO1 and FSO2 diet and significantly (P < 0.05) decreased in groups fed FSO3 and FSO4 diets. The best result in starvation tolerance test was obtained in FSO2 diet. The present study suggests that n‐3 and n‐6 PUFA ratio in broodstock diet has a considerable effect on spawning performance, egg and larval quality for C. semilaevis.     

The effects of dietary HUFA level on flame angelfish (Centropyge loriculus) spawning,egg quality and early larval characteristics

This study was conducted to determine the effects of dietary highly unsaturated fatty acids (HUFA) on flame angelfish (Centropyge loriculus) reproduction, and egg and larval quality. In the experiment, formulated diets containing 1.8, 2.9 or 3.6% n‐3 HUFA were fed to flame angelfish broodstock (n = 4) for 5 months. Mean fecundity (daily egg production), egg fertilization rates and embryo viability were used as indicators of egg quality. In addition, mean egg diameter, oil globule diameter, per cent hatch, larval size at hatch, per cent survival to yolk exhaustion and larval size at yolk exhaustion were recorded for each treatment. Flame angelfish fed the diet containing 3.6% n‐3 HUFA exhibited significantly increased fecundity, fertilization rates and embryo viability than fish that were fed the other two formulated diets. Egg diameter, egg oil globule diameter, larval size at hatch, larval survival to yolk exhaustion and larval size at yolk exhaustion from the 3.6% n‐3 HUFA broodstock treatment group were not significantly different from those derived from the Control broodstock treatment. These data revealed that flame angelfish egg quality could respond rapidly (within weeks) to maternal dietary changes. Results from this study further support that dietary HUFA composition can significantly affect broodstock reproductive performance as well as subsequent performance of eggs and larvae.     

Conditioning,maturation and year‐round natural spawning of orange‐spotted grouper,Epinephelus coioides (Hamilton, 1822), in recirculating aquaculture system

The present experiment was aimed at studying the conditioning, maturation and natural spawning of orange‐spotted grouper, Epinephelus coioides, in a recirculatory aquaculture system (RAS). Thirty fish (n = 30; 3.35 ± 0.05 kg) were stocked in a circular tank of 125 m³ capacity fitted with an RAS for conditioning and broodstock development. After 15 days, 15 fish were implanted with 17 α methyl testosterone and letrozole at the rate of 5 mg and 0.2 mg/kg body weight, respectively, for conversion from female to male. The gonadal development started after 1 month, and by 90th day, 63.53 ± 3.78% and 2.07 ± 0.84% of the oocytes attained a size of 400–500 μm and 500–600 μm respectively. Natural spawning commenced in the RAS from 4th month onward after stocking and spawning continued round the year. The spawning pair showed courtship behaviour with a typical vertical burst of swimming just before release of gametes. The total number of eggs spawned during 1 year was 47.23 million with spawning frequency varying form 5 to 13 times per month. The association of spawning events with new moon day (lunar cycle) weakened as time progressed. The mean monthly fertilization and hatching rates varied from 77.80 ± 3.34% to 83.70 ± 1.76% and 82.80 ± 4.21% to 88.33 ± 1.39% respectively. The study proved that RAS is an efficient system that provides a stable, controllable and conducive environment for year‐round natural breeding of orange‐spotted grouper.     

Modelling Atlantic mackerel spawning habitat suitability and its future distribution in the north‐west Atlantic

We investigated the effect of environmental conditions on Atlantic mackerel spawning habitat in the southern Gulf of St. Lawrence (sGSL). Based on generalized additive models, we (i) modelled the optimal spawning habitat of mackerel in the sGSL using daily egg production (DEP) in June, (ii) predicted known and new potential present spawning habitats in the GSL and the north‐west Atlantic, and (iii) assessed how they respond to future climate change. Our findings showed that both mackerel presence–absence and given‐presence DEP were associated with sea surface temperature (10–16.5°C), salinity above 31 and depth < 120 m. Adding zooplankton showed a marked effect on the DEP given‐presence compared to the presence–absence. Predictions of spawning habitats under present (1999–2012) and future scenario (2066–2085) conditions were estimated from the presence–absence model without zooplankton, using physical conditions of the BNAM. Under present conditions, our model predicted well the main spawning habitat in the sGSL and other known secondary spawning habitats in the northern GSL (nGSL), the western and southern Newfoundland, and the north‐west Atlantic coast. Under future conditions, our study suggests that spawning habitats in the sGSL and the nGSL would expand. Our results, therefore, suggest that mackerel could benefit from a warmer GSL, minimizing the potential for a northward migration of the stock due to decreasing suitability of the sGSL as its main spawning ground, and a new but spatially limited potential habitat in Newfoundland coasts. These results can be used to inform stock management and develop adaptive management plans in the context of climate change.     

Dietary branched‐chain amino acid supplementation affects growth and hepatic insulin‐like growth factor gene expression in yellowtail,Seriola quinqueradiata

We investigated the effect of dietary supplementation with a branched‐chain amino acid (BCAA) mixture (valine, leucine and isoleucine) on juvenile yellowtail (Seriola quinqueradiata) growth and hepatic insulin‐like growth factor (IGF) gene expression. Total dietary BCAA content was 8.1, 8.5, 9.0 and 9.8 g   kg^?1 for the control, 0.4%, 1.0% and 2.0% BCAA experimental groups, respectively. Body weight was measured on day 77, after which fish were fasted for 3 days and refed; the livers were then removed 3 or 9 h later for analysis of hepatic gene expression. Body weight significantly increased in the BCAA‐supplemented groups. Hepatic expression of IGF1 and IGF2 significantly increased in the 2% BCAA group at 3 and 9 h after refeeding. In the 1% BCAA group, hepatic IGF1 expression tended to be higher at 9 h than in the control group after refeeding. Also, hepatic IGF2 significantly increased at only 9 h after refeeding in the 1% BCAA group. In conclusion, dietary supplementation with crystalline BCAAs increased growth and hepatic expression of IGF1 and IGF2. These results suggest that dietary crystalline BCAA supplementation would be a valuable addition to yellowtail aquaculture practices.     

Spawning induction and seed production of Eastern little tuna,Euthynnus affinis (Cantor, 1849), in the post‐ and pre‐spawning seasons by hormonal treatment in a semi‐closed recirculation system with elevated temperature

We previously established a method for spawning induction in Eastern little tuna (ELT) Euthynnus affinis (Cantor, 1849) by administering a gonadotropin‐releasing hormone analog (GnRHa) during the natural spawning season in Japan (August–October). In order to establish seed production of ELT in the off‐spawning season, we first conducted three spawning induction trials by GnRHa administration from October 2011 to January 2012 using ELT broodstock (2 years old; three females and four males) maintained in a 10‐m³ tank with a semi‐closed recirculation system and static elevated temperature. Average water temperature and daily egg production in three trials lasting 11–15 days were 27.0 ± 0.09°C and 268 173 eggs (Trial 1), 27.0 ± 0.11°C and 277 9098 eggs (Trial 2), and 25.5 ± 0.39°C and 291 113 eggs (Trial 3) respectively. Mean fertilization rate and mean hatching rate were 70.4% and 60.5% (Trial 1), 83.9% and 79.6% (Trial 2), and 62.5% and 57.4% (Trial 3) respectively. We also succeeded in producing ELT larvae in the pre‐spawning season (April–July), although the quantity and quality of larvae produced were inferior to those produced in other calendar months. In trials involving periodic GnRHa administration during the off‐spawning seasons, hatched larvae were obtained in the 10‐m³ tank after six of nine administrations in the 2011–2012 off‐spawning season and in 16 of 19 administrations in the 2012–2013 off‐spawning season. The findings of this study demonstrated that hormonal treatment and thermal control could be used to extend the spawning period in ELT, potentially allowing larval production in the post‐ and pre‐spawning seasons.     

Year‐round natural spawning,early development,and the effects of temperature,salinity and prey density on captive ornate goby Istigobius ornatus (Rüppell, 1830) larval survival

Natural spawning, early development and larviculture of the ornate goby Istigobius ornatus in captivity were studied for the first time. I. ornatus spawned 46 times from 31 October 2013 to 31 October 2014. Fecundity ranged from 246 to 10,214 eggs per clutch, with an average hatching rate of 77.8% ± 9.9% (M ± SEM). Fertilized eggs (1.31–1.54 × 0.46–0.50 mm in diameter) were adhesive demersal and oval‐shaped. Embryonic development lasted 84 hr at 27.5 ± 0.5°C. Newly hatched larvae [2.12 ± 0.04 mm in total length (TL)] transformed to the juvenile stage completely when TL was 7.79 mm. Effects of different water temperatures (24, 28 and 32°C) and salinities (10, 15, 20, 25, 30, 35 and 40 g/L) on per cent survivals (%) and survival activity indices (SAIs) were tested. Survival was not significantly different under different temperatures; SAIs was significantly higher at 28°C. Larvae showed the significantly higher survival and SAIs at salinities 10–30 g/L than at 35 and 40 g/L. Effect of different prey densities on survival was significantly higher in 7 days post hatch larvae fed 20 and 30 rotifers/ml. These findings could guide future programs in captive breeding technology development and commercial production of other marine ornamental gobies.