Early Larval Growth of Pacific Halibut Hippoglossus stenolepis

Growth of Pacific halibut Hippoglossus stenolepis larvae was studied in the laboratory during 1989 and 1991. Larvae increased in length from 6.3 mm at hatching to 9.9 mm 20 d post-hatch. The average daily length increment was 0.17 mm. Dry weight of the larvae increased from an average of 210 μg at hatching to 570 μ g on day 20, providing a specific growth rate of 4.99. During the same period, mean yolk sac weight decreased from 1,390 μ g to 646 μ g, resulting in a yolk to body conversion efficiency of 48.5%. At hatching, the larval body made up only 13% of total dry weight. On day 20, the larval body made up 46.9% of the total weight. Larvae started feeding at a length of 12 mm after about 90% of their yolk sac had been absorbed.     

Compartmental changes in the contents of total lipid, lipid classes and their associated fatty acids in developing yolk-sac larvae of Atlantic halibut, Hippoglossus hippoglossus (L.)

Total lipid, lipid classes and their associated fatty acids have been measured in whole halibut, Hippoglossus hippoglossus (L.) larvae and in dissected animals separated into yolk and body compartments. At hatching the larval body contained 17 μg ind^?1 of lipid (11% of larval body dry weight), while the yolk contained 190 μg ind^?1. Phosphatidylcholine (PC) accounted for 57% of total yolk lipids while phosphatidylethanolamine (PE), triacylglycerol (TAG), cholesterol and sterol ester (SE) accounted for 12%, 12%, 9% and 6% respectively. The main fatty acids in the PC fraction were 22:6n-3 (25.6 μg ind^?1), 16:0 (19.2 μg ind^?1) and 20:5n-3 (12.6 μg ind^?1). Between hatch and 200 day-degrees post hatch (D°PH) a net decline in total lipids of 29% was seen. There seemed to be some, but relatively minor, changes in the relative composition of lipids in the yolk throughout development, which are indicative of a non-selective endocytotic bulk uptake of lipids from the yolk. Towards first-feeding there was a selective catabolism of PC and a net synthesis of PE in the developing body, resulting in a shift in the lipid class composition in the body compared with that of the yolk. The fatty acids released from lipid hydrolysis were mainly used as energy substrates by the growing halibut larvae; 22:6n-3 was quantitatively one of the most important fatty acid fuel in energy metabolism. At the same time 38% and 23% of the 22:6n-3 released from PC was retained by the PE and neutral lipids in the growing larval body respectively. Except for 20:5n-3 (2%, 14%) no similar retention was seen in any of the other fatty acids. The observed net synthesis of PE in developing yolk-sac larvae of Atlantic halibut and the preferential retention of 22:6n-3 into it, increasing from 28% at hatching to 45% at 200 D°PH, may point to a high biological value of this compound.     

Microbially matured water: a technique for selection of a non-opportunistic bacterial flora in water that may improve performance of marine larvae

Before transfer to larval incubators, water was membrane filtered to remove >95% of the bacteria and then transiently maintained in a biofilter that promoted recolonization of the water by non-opportunistic bacteria. The process is termed microbial maturation of the water. Hypothetically the bacterial flora in the matured water should protect the marine larvae from colonization and proliferation by opportunistic bacteria. Testing of the hypothesis demonstrated 76% higher survival of yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus) in matured than in membrane filtered water. Proliferation of opportunistic bacteria was observed in the rearing water after hatching of turbot eggs (Scophthalmus maximus), but to a less extent in the microbially matured water. In the early phase of first feeding of turbot larvae, the matured water induced qualitative differences in the gut microflora. Significantly higher initial growth rate of the turbot larvae in the matured water affected 51% higher average weight of 13 days old larvae than in membrane filtered water. Algal addition to the matured water enhanced the larval growth further. The experiments conducted supported the proposed hypothesis that microbial maturation selects for non-opportunistic bacteria, which protects the marine larvae from proliferation of detrimental opportunistic bacteria.     

The influence of rearing temperature on early development and growth of spotted wolffish Anarhichas minor (Olafsen)

Temperature influenced the developmental rate, survival and early growth of eggs and embryos of spotted wolffish, Anarhichas minor (Olafsen), an interesting candidate for cold water cultivation. The total incubation period decreased from 220 days at 4 °C (880 daydegrees), to 177 days at 6 °C (1062 daydegrees) and 150 days at 8 °C (1200 daydegrees) in these experiments. The proportion of normal embryos and survival of eggs until hatching were highest when the eggs were incubated at 6 °C. During the incubation period, the embryo and yolk sac size at 280 daydegrees was not significantly different but at 850 daydegrees the embryo size was inversely related to temperature and the remaining yolk sac size positively correlated with the incubation temperature. The transformation of yolk to body mass during incubation appeared to be most efficient at 4 °C, and the embryos hatched with a larger visible yolk sac at 6 and 8 °C. The largest larvae (wet‐weight) hatched from the largest eggs and the egg groups incubated at the lowest temperature (4 °C). There was no effect of temperature on meristic characters. During 6 weeks post‐hatching, all larvae from the three temperature groups were fed formulated dry feed in excess at 8 °C in low water‐level raceway systems. During startfeeding, the larvae from eggs incubated at the lowest temperature (4 °C) showed the highest growth rates (SGR). Best survival of larvae was noted among batches incubated at 6 °C.     

Influence of temperature and salinity on length and yolk utilization of striped bass larvae

The effects of temperature and salinity on yolk utilization and growth of larval striped bass (Morone soxatilis) from Canadian maritime stocks were studied to determine optimal rearing conditions. Larval length increased during yolk utilization and maximum length (L_max) was attained at about 70 degree-days post-hatch. Dry weight declined during yolk utilization, whereas, larval wet weight was relatively constant and only declined when yolk was depleted. Temperature and salinity significantly affected the L_max. Temperatures exceeding 18 C resulted in lower L_max. Higher L_max values were attained at 5 % than at 1 or 10 %. Time to reach L_max was longer at 5 and 10 % than at 1 % for any experimental temperature. Time to reach L_max was 3 days post-hatch longer than times to maximum embryo dry weight. The Q₁₀ of yolk utilization was 1.71, 1.53 and 2.52 at 1, 5 and 10 %, respectively. Times to terminal yolk utilization were about 1.2 d shorter than times to L_max. Morphological changes during yolk utilization indicated rapid development of locomotory and predatory capabilities. These and other developmental strategies were compared to those of salmonids. Rearing striped bass larvae at 14 \-16C and 5 % throughout yolk utilization should result in longer larvae at initial first feeding.     

Folate in eggs and developing larvae of Atlantic halibut, Hippoglossus hippoglossus L.

Folate mobilization from the yolk compartment during larval development was studied by analysing the folate concentration in whole body, embryo and yolk in a single batch of Atlantic halibut, Hippoglossus hippoglossus L., eggs and larvae that showed successful fertilization and development. There was a net loss of approx. 50% of folate from yolk during endogenous feeding. Further, only 23% of the decrease in yolk folate was retained in the larval body. The data suggest a need for folate for metabolic and growth purposes during embryogenesis of approximately 2 μg g^?1 weight gain. Relative to these data and published folate requirement for cold‐water species, batches of egg from 16 Atlantic halibut brood fish contained variable and, for some batches, critically low levels of folate. This may constitute a potential problem for larval development until start feeding.     

Time of first feeding of Atlantic halibut, Hippoglossus hippoglossus L., larvae

Atlantic halibut, Hippoglossus hippoglossus (L.), eggs originating from one female were evenly distributed between four silos (4.8 m³) shortly prior to hatching. At days 30, 35, 40 and 44 after hatching [i.e. 200, 230, 260 and 290 day-degrees (days^o)], the larvae were successively collected and transferred to indoor start feeding tanks, and larvae were offered a diet of instar II Artemia nauplii which had been enriched short time (24 h). A significant correlation was found between the age of the larvae and onset of first feeding. The larvae transferred to start-feeding incubators at 290 days^o were able to capture Artemia only a few hours after transfer, whereas it took 6 days for the larvae transferred at 200 days^o to reach a corresponding ingestion level. Larval growth was also positively correlated to both larval age and prey consumption. However, there were no differences in survival between the larval groups.     

Effects of incubation water hardness and salinity on egg hatch and fry survival of Nile tilapia Oreochromis niloticus (Linnaeus)

This study examined the effects of water hardness and salinity on yolk sac larvae and swim‐up fry survival of Nile tilapia, Oreochromis niloticus (Chitralada strain), eggs during artificial incubation. Four experiments were conducted to evaluate the effects of hardness, salinity and the sources of saline incubation water. High water hardness treatments (500–4200 mg L^?1 as CaCO₃) resulted in higher yolk sac larvae and swim‐up fry survival than low water hardness treatments (50.0 and 132 mg L^?1 as CaCO₃); although yolk sac larvae and swim‐up fry survival did not differ among the high or low hardness treatments. Salinity of 4.0 g L^?1 using seawater, and 4.0 and 8.0 g L^?1 using unprocessed common salt resulted in the higher survival rate of yolk sac larvae and swim‐up fry than other salinity treatments. Yolk sac larvae and swim‐up fry survival was found to decrease with the increase in salinity and increase with the increase in water hardness. The present study demonstrated the positive effects of increased water hardness level (>132 mg L^?1) on yolk sac larvae and swim‐up fry survival. The study also showed that seawater salinity of 4 g L^?1 was the most appropriate salinity level for incubating Nile tilapia eggs.     

Change in nutrient composition of Artemia grown for 3–4 days and effects of feeding on‐grown Artemia on performance of Atlantic halibut (Hippoglossus hippoglossus,L.) larvae

Major challenges in culture of Atlantic halibut larvae have been slow growth during the late larval stages and inferior juvenile quality due to pigmentation errors and incomplete eye migration during metamorphosis. The hypothesis of this study was that feeding on‐grown Artemia would alleviate these problems. Artemia were grown for 3–4 days on Origreen or Origo. The growth and nutrient composition of Artemia nauplii and on‐grown Artemia were analysed, and both Artemia types were fed to Atlantic halibut larvae, on‐grown Artemia from 15 days post‐first feeding (dpff). The body length of Artemia increased with 20%–70% in response to on‐growing. In all experiments, protein, free amino acids and the ratio of phospholipid to total lipid increased, while lipid and glycogen decreased. The fatty acid composition improved in some cases and not in others. The micronutrient profiles were not negatively affected in on‐grown Artemia. All these changes are thought to be beneficial for marine fish larvae. The final weight of Atlantic halibut postlarvae was similar, and 90% of the juveniles had complete eye migration in both groups. It is concluded that the present version of Artemia nauplii probably covers the nutrient requirements of Atlantic halibut larvae.     

Effects of egg disinfection and incubation temperature on early life stages of spotted wolffish

Eggs of spotted wolffish (Anarhichas minor Olafsen)were incubated at constant 4, 6 and 8 °C, and disinfected withglutaric dialdehyde (150 p.p.m. for 5 min) once ortwice a month during two thirds of the incubation period, to prevent growth ofmicroorganisms. Hatching of apparently normal larvae started earlier when eggswere disinfected twice a month compared to once a month at all incubationtemperature regimes. The time to 50% hatch was 900 and 920 day-degrees (16 and16,5 weeks) at 8 °C, 835 and 880 day-degrees (20 and 21 weeks)at 6 °C and 725 and 800 day-degrees (26 and 28,5 weeks) at 4°C, in the egg groups disinfected twice or once a month,respectively. The best survival until hatching was noted when eggs weredisinfected twice a month and incubated at 6 and 8 °C.Survivalwas very low at 4 °C. Prematurely hatched larvae wereregistered in all egg groups disinfected twice a month and the highestfrequencywas noted in the 8 °C groups. The larval weight at normalhatching in the 6 and 8 °C groups was negatively correlatedwith incubation temperature and intervals of disinfection during the incubationperiod, but after 42 days feeding with live feed (unenrichedArtemia) the weights of the larvae were not significantlydifferent. The specific growth rates of the larvae from the eggs incubated at 6°C and 8 °C were 3.0% and 3.2%, respectively.The mean survival of larvae was between 88% and 96% at 42 days post-hatching.Young wolffish originating from the 6 °C incubation groupsshowed lowest mortality.     

Effect of recovery salinity on survival of acutely stressed halibut (Hippoglossus hippoglossus L) larvae

First‐feeding halibut larvae (245‐day degrees; 40 days post hatch), reared at 34 g L^?1 salinity and 7°C, were subjected to handling and allowed to recover in a range of salinities (0–34 g L^?1) and at 10°C. Survival of the unfed larvae was determined daily for 18 days. Mortality rates approached 0 after 4 days in all treatments and presumed starvation‐induced mortality started at about 11 days post handling. By 20 days post treatments, all larvae had died. Salinities in the range of 10–20 g L^?1 produced significantly (anova , P<0.01) higher initial survival (71–95%) than salinities above 20 g L^?1 (24–48%) or below 10 g L^?1 (0–19%) and this survival pattern changed little in unfed larvae for the first 10 days following the stressor. For example, 24 hour post handling, survival of halibut was improved from 28.7±16.5% (mean±standard error, n=3) at 34.0 g L^?1 to 95.2±4.8% at 13 g L^?1. A second‐order polynomial regression of 4‐day post‐handling survival data (y=?0.002x ²+0.0603x+0.0699, r²=0.3936) predicted a maximum survival at 15.1 g L^?1 salinity. These results have important implications for halibut aquaculture and research when handling of larvae is unavoidable. For practical applications, we recommend reducing salinity of receiving waters to 15–20 g L^?1 with a slow (3–4 days) reacclimation to ambient conditions.     

The Effects of Temperature and Salinity on Early Life Stages of Black Sea Bass Centropristis striata

Along the Atlantic coast black sea bass occur from the Gulf of Maine to Florida and support important commercial and recreational fisheries. Interest in commercial production of black sea bass has increased in recent years due to high demand and limited seasonable availability. Efforts towards large-scale production have been hampered by a high incidence of early larval mortality. Two of the most important environmental variables affecting hatchery production of marine finfish larvae are temperature and salinity. In the wild, larval black sea bass are found in waters with temperatures of 12–24 C and salinity levels of 30–35 ppt. Studies were conducted to define the temperature and salinity ranges that support growth and development of black sea bass during early life stages. Three developmental phases were investigated: 1) fertilization to hatch: 2) hatch through yolk sac absorption: and 3) during the initial exogenous feeding stage (5–14 days post hatch: DPH). Fertilized eggs were obtained by manual spawning of fish following administration of LHRH_a. Fertilized eggs were transferred to 300-mL glass Petri dishes or 500-mL beakers to assess the effects of salinity and temperature through hatch and yolk sac absorption, respectively. To determine environmental effects on growth and survival during initial exogenous feeding 400 actively feeding larvae were cultured in green water and fed enriched rotifers for a 9-d period. For investigation of the effect of salinity, sea water (35 ppt) was diluted gradually to 15, 20, 25, and 30 ppt and maintained at 21 C. For examination of the effect of temperature, seawater was adjusted from 21 C to 12, 15, 21, 27, or 30 C at a rate of 3 C/h. No eggs hatched at 12 C or when salinity was maintained at 0 or 5 ppt. Hatching was uniformly high (≥ 85%) at temperatures between 15 and 27 C and at salinities ≥ 15 ppt. Survival through yolk sac absorption was greatest at temperatures between 18 and 27 C and at salinities ≥ 20 ppt. Survival through first feeding stage was highest at temperatures ≥ 18 C and 30 ppt salinity. Larval growth through first feeding was not significantly affected by salinity level but did increase with rearing temperature. The results indicate that survival and development of black sea bass during early life stages are most favorable at temperatures >18 C with salinity levels approaching full strength seawater.     

Incorporation of yolk fatty acids into body lipids of goldfish (Carassius auratus L.) larvae raised at two different temperatures

In five separate experiments, eggs from a single female goldfish were fertilized at 20°C. They were incubated at 22°C for 6 hours, after which some of the eggs were transferred to 13°C. When a defined post-hatch developmental stage was reached, lipid extracts were prepared from larvae, both with yolk sacs intact and after removal of the yolk sac by dissection. Other larvae were sampled at yolk exhaustion. Gas chromatographic analysis of fatty acid profiles revealed that larvae incorporated 16:0, 18:0, 20:4 (n–6) and 22:6 (n–3) into their tissues in proportions higher than those present in the eggs from which they were derived. At 22°C, these trends were particularly apparent at yolk exhaustion. At 13°C, proportions of polyunsaturated fatty acids in the bodies of newly hatched larvae were higher than those in the 22°C larval bodies. Monounsaturated fatty acids were preferentially depleted during development, especially in larvae from high quality eggs. No dependence of egg quality, as assessed by larval viability at 22°C, on total egg lipid mass or fatty acid composition was found. Larvae from the lowest quality eggs showed a reduced preference for incorporation of (n–3) polyunsaturated fatty acids into their tissues.     

Bacteria associated with early life stages of halibut, Hippoglossus hippoglossus L., inhibit growth of a pathogenic Vibrio sp.

Abstract Bacteria capable of inhibiting growth of a pathogenic Vibrio sp. were isolated from the gastrointestinal tract of cultured halibut larvae during the first feeding and weaning stages. No such bacteria were found among isolates from the surface of eggs or the gastrointestinal tract of yolk sac larvae. The fraction of pathogen-inhibitors among the total number of isolates ranged between 0–100% (first feeding) and 0–66% (weaning). All pathogen-inhibitors were Gram-negative rods, and 95% were oxidase and catalase positive fermentative isolates, capable of producing acid aerobically from a varying range of carbohydrates. These isolates possessed the characteristics of the Vibrio/Aeromonas -group, but only 19% were sensitive to the vibriostatic agent 0/129. Isolates from eggs and yolk sac larvae were dominated by bacteria belonging to the Cytophaga/Flexibacter/Flavobacterium - group. The high fraction of isolates with the ability to inhibit growth of the pathogenic Vibrio sp. among the total number of isolates indicates that pathogen inhibition may be an important mutualistic role of the intestinal flora of early life stages of halibut.     

A comparison of retinol, retinal and retinyl ester concentrations in larvae of Atlantic halibut (Hippoglossus hippoglossus L.) fed Artemia or zooplankton

Atlantic halibut (Hippoglossus hippoglossus L.) larvae were fed enriched Artemia or zooplankton in duplicate tanks from 0 to 60 days after first‐feeding. Both diets and the larvae were analysed for vitamin A (VA) in order to confirm earlier findings, in which Artemia fed larvae had lower levels of VA compared with larvae fed zooplankton. Furthermore, we wanted to investigate the composition of the retinoids in the larvae. The results showed that Artemia and zooplankton contains low levels of VA, probably too low to sustain the assumed requirement. Nevertheless, larvae fed Artemia had the same level of retinal and retinol as larvae fed zooplankton. We found a significant lower level of retinyl esters in larvae fed Artemia. The total VA level was lower in larvae fed Artemia only at the end of the feeding trial after the onset of metamorphosis. Our conclusion is that feeding Artemia to Atlantic halibut larvae is not likely to cause VA deficiency.     

Experimental infection of eggs and yolk sac larvae of halibut, Hippoglossus hippoglossus L.

Abstract Scanning electron micrographs of halibut eggs with an epiflora dominated by Flexibacter sp., showed ulcerations colonized by large numbers of bacteria. The chorion was dissolved in most ulcerations and the zona radiata was severely damaged. Infection experiments showed that exposure to these bacteria caused high mortalities at the late egg stage, hatching and the early yolk sac stage. Eggs exposed to three different Vibrio spp. showed different mortality patterns, with low mortality at hatching, followed by a continuous high mortality throughout the yolk sac stage. Mortality in the uninfected control group was low throughout the experiment. Transmission electron microscopy of the Vibrio -infected larvae showed bacteria present in the gill, heart and frontal yolk sac regions.     

Mortality processes of hatchery‐reared Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) larvae in relation to their piscivory

In mass culture of Pacific bluefin tuna Thunnus orientalis, yolk‐sac larvae of other species are fed as a major prey item to tuna larvae from 7 to 8 mm in total length. Marked growth variations in tuna larvae are frequently observed after feeding of yolk‐sac larvae, and this variation in the growth of tuna larvae is subsequently a factor leading to the prevalence of cannibalistic attacks. To elucidate details of the mortality process of hatchery‐reared tuna larvae after the initiation of yolk‐sac larvae feeding, we compared the nutritional and growth histories of the surviving (live) tuna larvae to those of the dead fish, found dead on the bottom of the tank, as direct evidence of their mortality processes. Cause of mortality of tuna larvae 3 and 5 days after the initiation of feeding of yolk‐sac larvae was assessed from nitrogen stable isotope and otolith microstructure analyses. Stable isotope analysis revealed that the live fish rapidly utilized prey fish larvae, but the dead fish had depended more on rotifers relative to the live fish 3 and 5 days after the initiation of feeding of yolk‐sac larvae. The growth histories based on otolith increments were compared between the live and dead tuna larvae and indicated that the live fish showed significantly faster growth histories than dead fish. Our results suggest that fast‐growing larvae at the onset of piscivory could survive in the mass culture tank of Pacific bluefin tuna and were characterized by growth‐selective mortality.     

Combined effects of temperature and salinity on development and survival of Atlantic halibut larvae

The effects of different combinations of temperature and salinity on development and survival of Atlantic halibut, Hippoglossus hippoglossus (L.), larvae were studied in two experiments. In the period from 57 to 120 d° post hatching, approximately 38% of the larvae died: in both experiments, mortality was significantly related to temperature, but there was no relationship to salinity.Cumulative, chronic mortality during the yolk-sac stage (until 210 d°) was related to salinity. High mortality was observed in both experiments when high salinity (>34%) was combined with incubation at either high (9 °C) or low (3 °C) temperature. The development of head lesions was significantly related to temperature, and for larvae kept at high salinity, increased mortality may have been a result of salinity stress in the injured larvae.Abnormal development of the caudal notochord, sometimes resulting in a 90-degree bend of the tail, occurred during incubation of early yolk-sac larvae in high-salinity water. The occurrence of larvae with locked jaws, and larvae with oedema in the yolk-sac sinus and pericardium, was significantly related to temperature. © Rapid Science Ltd. 1998     

Relationship between prey utilization and growth variation in hatchery‐reared Pacific bluefin tuna,Thunnus orientalis (Temminck et Schlegel), larvae estimated using nitrogen stable isotope analysis

In mass culture of Pacific bluefin tuna Thunnus orientalis, a marked growth variation is observed after they start feeding at 6–7 mm in body length (BL) on yolk‐sac larvae of other species, and the growth variation in tuna larvae is a factor leading to the prevalence of cannibalism. To examine the relationship between prey utilization and growth variation, nitrogen stable isotope ratios (δ¹⁵N) of individual larvae were analysed. A prey switch experiment was conducted under two different feeding regimes: a group fed rotifers (rotifer fed group), and a group fed yolk‐sac larvae of spangled emperor, Lethrinus nebulosus (fish fed group) from 15 days after hatching (6.87 mm BL). The fish fed group showed significantly higher growth than the rotifer fed group. Changes in the δ¹⁵N of the fish fed group were expressed as an exponential model and showed different patterns from those of the rotifer fed group. The δ¹⁵N of fast‐growing tuna larvae collected in an actual mass culture tank after the feeding of yolk‐sac larvae was significantly higher than those of the slow‐growing larvae, indicating that slow glowing larvae depended largely on rotifers rather than the yolk‐sac larvae.     

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.