Morphological development and allometric growth of yellowtail kingfish Seriola lalandi V. larvae under culture conditions

Morphological development and allometric growth patterns of Seriola lalandi larvae were assessed to characterize normal growth patterns under culture conditions. Early ontogenetic stages of yellowtail kingfish exhibited an exponential growth in terms of standard length as a function of age. Five development stages were characterized from hatching to the juvenile stage: larval stage I (0–2 days post hatch, dph) with endogenous feeding, characterized by a small yolk sac, unpigmented eyes, primordial finfold surrounding the body and a closed mouth; larval stage II (2–15 dph) characterized by mouth opening, complete pigmentation of eyes and the beginning of the exogenous feeding; subsequently, in the larval stage III (15–25 dph) the posterior tip of notochord of the larvae bended upward and the first rays appeared in fins, concomitant with a change in swimming behaviour; thereafter, larval stage IV (post‐flexion stage; 25–30 dph) began when larvae resembled in morphology to a juvenile organism; however, caudal and dorsal fins were not completely development. Lastly, the juvenile stage was reached 30 dph characterized by a morphology and fin structures similar to those of the adults. Growth and development of structures and organs associated with vital functions such as feeding, sensorial and breathing systems seemed to be more critical previous to 23 dph, which was reflected with a positive allometric growth of head and eyes during this period. The results from this study can be used as a tool‐guide to assess normal development in larval research with S. lalandi to improve existing rearing protocols in hatchery production.     

Effect of cultivated copepods (Acartia tonsa) in first‐feeding of Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae

The aim of this study was to compare the nutritional composition and effects of short periods with cultivated copepod nauplii versus rotifers in first‐feeding. Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae were given four different dietary regimes in the earliest start‐feeding period. One group was fed the copepod Acartia tonsa nauplii (Cop), a second fed enriched rotifers (RotMG), a third fed unenriched rotifers (RotChl) and a fourth copepods for the seven first days of feeding and enriched rotifers the rest of the period (Cop7). Cod larvae were fed Artemia sp. between 20 and 40 dph (days posthatching), and ballan wrasse between 36 and 40 dph, with weaning to a formulated diet thereafter. In addition to assessing growth and survival, response to handling stress was measured. This study showed that even short periods of feeding with cultivated copepod nauplii (7 days) had positive long‐term effects on the growth and viability of the fish larvae. At the end of both studies (60 days posthatching), fish larvae fed copepods showed higher survival, better growth and viability than larvae fed rotifers. This underlines the importance of early larval nutrition.     

Embryonic development in corkwing wrasse,Symphodus melops

Corkwing wrasse, Symphodus melops, is one of the main species used as cleaner fish to combat sea lice infestation in salmon aquaculture; however, there is little knowledge about its biology. Here, we describe the embryonic development of this species and examine the viability of the eggs under three temperature regimes. The experiments were conducted at three water temperature regimes, 12, 15, and 18°C, which resemble common sea water temperatures registered during the spawning season of corkwing wrasse at different latitudes along the Norwegian coast. Corkwing wrasse spawn small spherical eggs of 0.75–0.80 mm in diameter (mean 0.78, CV = 3.6%) with several oil droplets and go through eight developmental stages until hatching. The shortest hatching time was registered after 144 hr at 18°C and after 222 and 372 hr at 15 and 12°C, respectively. These observations provide important baseline biological information to advance the establishment of commercial rearing techniques and sustainable fishing management practices for this heavily exploited species.     

Nile tilapia broodfish fed high‐protein diets: Digestive enzymes in eggs and larvae

The aim of this study was to assess the activity of gastric, pancreatic and intestinal digestive enzymes during the embryonic and larval development of Nile tilapia (Oreochromis niloticus) GIFT strain Aqua America^® 1 obtained from a broodstock fed two levels of crude protein (CP). A total of 72 females and 24 males, 10 hapas, two CP levels (32% and 38%) and six phases of embryonic (cleavage, blastula, gastrula) and larval (hatching, 7 and 10 days post hatch, dph) stages were used. The eggs were collected in cleavage, blastula and gastrula stages, 300 mg was collected, and kept in cryogenic tubes in liquid nitrogen. For the samples at larval stage, the remaining eggs were separated according to crude protein level and kept in hatcheries and samples were collected on 7 and 10 dph the same way as before. A total of 48 samples were collected: at each protein level (32% and 38% CP), four samples were collected in each phase of embryonic and larval development. Statistical differences were not observed during embryonic development for acid proteases, trypsin, amylase and lipase activity at both levels of crude protein (32 and 38% CP). Differences for acid proteases were noticed on 7 dph; trypsin and amylase on 7 dph and 10 dph. Significant differences on blastula and 7 dph for protease; as for aminopeptidase, there was significant difference on 7 dph. The data indicated early appearance of digestive enzymes in Nile tilapia broodfish receiving 32% CP taking into account the rapid growth and development of this species.     

Larval development in European hake (Merluccius merluccius L.) reared in a semi-intensive culture system

Eggs of European hake (Merluccius merluccius L.) were stripped from fish caught at sea. Larvae were kept under semi‐intensive conditions at around 12°C. In addition, eggs were incubated in single wells at 9.2, 12.7 and 14.5°C, where hatching, development and survival were closely examined. During the larval stage, a total of 299 larvae were sampled to follow development and growth. In addition a small number of juveniles were sampled. Larvae hatched approximately 4 days after fertilization, and were 2.9 mm in total length (TL). At 6‐day post hatching (dph), the larvae were 4.1 mm (TL), the jaw apparatus was developed, and the larvae had started to feed. Most of the growth during the early larval period is restricted to the head, and there is almost no increase in length for the first 3–4 weeks post hatching. Teeth and pelvic fins appear at 25 dph. Development of unpaired fins at approximately 30 dph marks the start of the larval–juvenile transition. Weaning to formulated feed was accomplished 50 dph, when external morphology was similar to that of adult hake.     

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.     

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.     

Physiological stress responses to captivity in early developmental stages of the wedge sole Dicologoglossa cuneata (Moreau)

The stress responses in early growth stages of the wedge sole have been studied to determine whether the high cortisol levels described in juvenile fish are present from early developmental stages. Whole‐body cortisol, glucose and lactate contents, as well as biometric parameters in wedge sole larvae were measured at three different stocking densities. Stocking density affected growth‐related variables significantly, and larvae in lower stocking densities grew faster. Survival did not significantly differ among treatments. At hatching, the whole‐body cortisol concentration was 0.33 ± 0.01 ng g^?1 and varied significantly from 0 to 30 days after hatching (DAH) for each stocking density, though values remained stable for the remaining time in the low‐stocking density group. These hormone levels rose significantly (5.17 ± 2.43 to 22.10 ± 4.95 ng g^?1) at the end of the experiment, depending directly on the stocking density. Glucose and lactate‐body concentrations did not vary among treatments. We conclude that the stress responses of wedge sole larvae are detectable from 45 DAH and that stocking density already can be a stressor at that age. As described for juvenile stage, cortisol content values in wedge sole larvae under non‐stressful conditions are one of the highest among those reported in the literature. The captivity conditions could be responsible for this apparently stressful situation, though those values also could be normal in wild specimens.     

Immunostimulatory effects of dietary poly‐β‐hydroxybutyrate in European sea bass postlarvae

The stable production of high‐quality fry in marine aquaculture is still hampered by unpredictable mortality caused by infectious diseases during larval rearing. Consequently, the development of new biocontrol agents is crucial for a viable aquaculture industry. The bacterial energy storage compound poly‐β‐hydroxybutyrate (PHB) has been shown to exhibit beneficial properties on aquatic organisms such as enhanced survival, growth, disease resistance and a controlling effect on the gastrointestinal microbiota. However, the effect of PHB on the developing immune system of fish larvae has so far not been investigated. In this study, the effect of feeding PHB‐enriched Artemia nauplii on survival, growth and immune response in European sea bass (Dicentrarchus labrax) postlarvae was examined. Amorphous PHB was administered to 28‐day‐old sea bass postlarvae over a period of 10 days. The survival and growth performance were monitored, and the expression of 29 genes involved in immunity, growth, metabolism and stress‐response was measured. While the expression of the insulin‐like growth factor 1 (igf1), an indicator of relative growth, was upregulated in response to feeding PHB, the larval survival and growth performance remained unaffected. After 10 days of PHB treatment, the expression of the antimicrobial peptides dicentracin (dic) and hepcidin (hep) as well as mhc class IIa and mhc class IIb was elevated in the PHB fed postlarvae. This indicates that PHB is capable of stimulating the immune system of fish early life stages, which may be the cause of the increased resistance to diseases and robustness observed in previous studies.     

Is it possible to successfully rear meagre (Argyrosomus regius Asso 1801) larvae without using rotifers?

In hatcheries, meagre Argyrosomus regius larvae still depend on an adequate supply of rotifers and Artemia, as no artificial diet can totally fulfil their nutritional requirements. However, production of live feed is highly expensive and demands intensive labour and specific facilities. This study investigated the effect of a dietary regime without the use of rotifers, to simplify the meagre larval rearing protocol. Two feeding treatments (T₁ & T₂) are compared to investigate their effects on survival and growth of meagre larvae. In T₁, larvae were fed rotifers from 2 to 5 days post hatch (dph), and Artemia from 4 to 15 dph. In T_2, larvae were kept under dark conditions and fed Artemia from 6 to 15 dph. Standard larval length (SL) was significantly higher in T₁ (p < .01) until 8 dph in comparison with larvae reared initially without rotifers. No significant difference in SL was found among treatments (p = .187) at 15 dph. Significant difference was found among treatments in survival rate at 15 dph (p < .003). The survival rate observed at 15 dph in T₂ (30 ± 4.2%) represents an important finding, although the highest survival rate was observed in T₁ (45.0 ± 3.4%). This study showed that it is possible to conduct larval rearing of meagre without using rotifers. Nevertheless, further research efforts are still needed to improve these results in comparison with the common larval rearing protocol.     

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.     

Qualitative analysis of cartilaginous jaw element malformation in cultured yellowtail kingfish (Seriola lalandi) larvae

A central problem facing worldwide culture of yellowtail kingfish (Seriola lalandi) is the presence of skeletal malformations, including jaw deformities. This study presents a morphological characterization of normal and abnormal cartilage jaw structures during early larval development. Samples of 70–150 larvae were collected from three cohorts from 2 to 9 days post hatching, anaesthetized and fixed for cartilage staining. Cartilaginous components were defined clearly at four days post hatch (dph) (4.65 ± 0.05 mm total length), and abnormal jaw structures were detectable at this time. Jaw deformities observed included extension of Meckel's cartilage with or without ventral bending of the anterior tip, displacement of ceratohyal and hypohyal cartilage ventrally and below Meckel's cartilage, and shortening and dorsal flexion of the lower jaw. At 4 dph, between 44% and 47% of all larvae examined had jaw abnormalities. The contribution of each deformity to the total number of deformities was variable among the three cohorts examined. To compare shape difference accurately we performed an exploratory, landmark‐based geometric morphometric analysis using seven homologous landmarks. Larvae were classified into three jaw morphology groups. The geometric morphometric approach provides a useful tool to standardize classification of cartilage jaw abnormalities at early developmental larval stages. Early recognition of developing abnormalities is of importance for fish farmers in both improving fish selection efficiency and for evaluating effects of rearing parameters.     

Intra‐cohort cannibalism in early life stages of pikeperch

Cannibalism has been described in 390 teleost fish species belonging to 104 families. In rearing conditions, intra‐cohort cannibalism is one of the major bottlenecks during the early life stages of pikeperch (Sander lucioperca). This study aims to describe precisely the occurrence and the onset of cannibalism of this species during the first two post‐hatching months. In a first step, the cannibalistic behaviour was analysed through observations in three experiments. In each experiment, the number of cannibalistic cases was similar. From 14 to 48 days post‐hatching (dph), more than 60 % of prey ingestions were realized by tail‐first, but after 48 dph, the number of prey ingestions by head‐first increased. In a second step, the behavioural sequence exhibited to attack and to capture a conspecific was analysed, taking into account the size ratio between the cannibal and its prey. The behavioural sequence to capture was always the same, similar to a predatory sequence and it seems that the cannibal chose its prey about 10 s before attacking. Moreover, prey choice by a cannibal was based more on the size ratio between the cannibal and its prey than the previous activity of the potential prey. These new results could lead to solutions to decrease cannibalism in pikeperch rearing.     

Aggressive behaviour and cannibalism in greater amberjack,Seriola dumerili : effects of stocking density,feeding conditions and size differences

Aggressive behaviour, assessed by 24‐h observations, and survival rates, determined in a 2‐week rearing experiment, were examined in greater amberjack, Seriola dumerili, subjected to single and multiple factors (high density, restricted feeding and diverse size). Aggressive behaviour frequency in the group subjected to both restricted feeding and size diversity (FS) was significantly higher than that in the other groups (Tukey, n=4, P<0.05). In the FS group, aggressive behaviour increased with the starvation time from 19 days post hatching (dph) to 23 dph (two‐way analysis of variance, Tukey, n=4, P<0.05), but decreased gradually thereafter to 46 dph. In the rearing experiment, the survival rates for the diverse size and FS groups were lower than those of the control or restricted feeding groups (Kaplan–Meier, log‐rank test, n=100, P<0.01). Daily mortality in all groups was the highest at 24 dph; although dead fish were usually small, disappearance due to cannibalism was not observed during the rearing period. The results indicate that aggressive behaviour in greater amberjack is induced by hunger and size diversity in the early juvenile stages (23 dph). Mass mortality during seedling production was mainly caused by injury and the death of small fish due to aggressive behaviour/cannibalism.     

The effect of light intensity on performance of larval pike-perch (Sander lucioperca)

In this work performance parameters of larval pike-perch (Sander lucioperca) reared under four different light intensities (100, 500, 1000 and 2500 lx) until 21 days post hatch (dph) were investigated. As performance parameters change in length and weight, swim bladder inflation, feed consumption, natural mortality, stress induced mortality and RNA-DNA ratio were measured. Aim was to investigate the influence of light intensity on pike-perch performance during the first three weeks of larval rearing. Significant differences were found in natural and stress induced mortality as well as in weight growth. No single light exposure level combined optimal performance of all tested performance parameters. Highest light intensity of 2500 lx showed good weight growth but an increase in stress induced mortality. Bright light of 500 and 1000 lx intensity was found to improve growth and stress mortality whereas dim light conditions of 100 lx showed significantly lower natural mortality. Thus data suggested that most favorable illumination during larval pike-perch rearing comprise a tradeoff between optimal natural mortality under dim light conditions (100 lx) or optimal larval growth and stress resistance under bright light conditions (500 and 1000 lx). It is shown that high light intensities during larval rearing can be beneficial for pike-perch rearing if offspring supply is not limited.     

The Effect of Temperature on First Feeding, Growth, and Survival of Larval Witch Flounder Glyptocephalus cynoglossus

Witch flounder Glyptocephalus cynoglossus has recently been identified as a candidate species for aquaculture in the northeastern United States and the Canadian Atlantic Provinces. This study investigated the optimal temperatures for witch flounder larval first feeding and for long term larval culture from hatching through metamorphosis. Maximum first feeding occurred between 15.0 and 16.2 C. Larvae did not survive beyond first feeding when reared at mean temperatures of 5.1, 10.4, or 19.5 C and were unable to initiate feeding at mean rearing temperatures below 6.0 C. At a rearing temperature of 15.0 C in 16-L tanks, mean larval survival to 60 days post hatch (dph) was 14.1%. Mean overall length-specific growth rate for larvae reared to 60 dph at 15.0 C was 3.5%/d and mean absolute growth was 0.62 mm/d. Subsequent larval growth at 15.6 C began to taper off towards 70 dph at the onset of weaning which overlapped with larval metamorphosis. Growth plateaued at 85 dph, followed by a rebound between 90 and 95 dph. Survival was 100% when weaning onto a dry, pelleted diet was initiated at 70 dph with a 10-d live diet co-feeding period. These results are favorable and encourage the further pursuit of commercial witch flounder culture.     

Effects of two culturing techniques on the growth, survival and larval quality of Dentex dentex Linnaeus, 1758

Common dentex larvae were reared using two culturing techniques, mesocosms and intensive rearing, to determine the principal culture parameters involved in the differences observed in growth, skeletal deformations and survival between the two rearing techniques. In growth, only dry weight of larvae of 40 days post‐hatching (dph) from mesocosms was significantly higher than larvae from intensive rearing. Significant differences were observed in survival at 40 dph (6.58% in mesocosms and 1.58% in intensive rearing) and in the incidence of skeletal deformations, both for percentage of deformed larvae and for some deformation types such as those related to vertebral column and to the caudal complex. Initial larval density and initial prey density and quality are the factors suspected to affect growth and survival performance, while skeletal deformities might also be affected by tank hydrodynamics.