Amos Tandler

The effect of dietary arachidonic acid (20:4n - 6) on growth, survival and resistance to handling stress in gilthead seabream (Sparus aurata) larvae

Abstract The effects of high dietary docosahexaenoic acid (22:6 n −3, DHA) and varying arachidonic acid (20:4 n −6, AA) were tested on growth, survival and resistance to handling stress in 5–35 day old gilthead seabream larvae. Three enrichment treatments differing in their DHA/AA ratios were fed to rotifers ( Brachionus rotundiformis ) and Artemia nauplii. The high DHA (35.9% TFA) enrichment treatment (DHA-PL) contained no AA and included lipid from the heterotrophically grown DHA-rich dinoflagellate Crypthecodinium sp. A second enrichment treatment (AADHA), selected from an earlier screening study, supplemented the high DHA enrichment treatment with an AA-rich lipid (52% TFA) from the heterotrophically grown fungus Mortierella alpina. A third enrichment treatment (ALGA) was the commercial product Algamac 2000, which is devoid of AA, but includes approximately 12.9% of TFA as docosapentaenoic acid (DPA, 22:5 n −6). Rotifers fed the DHA-PL, AADHA and ALGA treatments demonstrated a range of DHA/AA ratios (20.9, 5.6 and 10.1, respectively) as did the Artemia nauplii (25.8, 3.7 and 4.6, respectively). The enriched rotifers were fed to larvae reared in 400 l V-tanks from day 5 to day 19 post-hatching. Following this period, larvae were exposed to controlled handling stress during transfer to 27 l aquaria, where they were then fed the enriched nauplii from day 20 to day 35 post-hatching. Although larval fatty acid profiles reflected the enrichment treatments, there were no marked differences ( P >0.05) in survival and growth in 5–19 day old larvae at the end of rotifer feeding. However, the larvae fed the AA enriched rotifers prior to the handling stress of transfer to the aquaria demonstrated daily and significantly ( P Artemia feeding than larvae fed the AA-deficient (DHA-PL) and ALGA-enriched rotifers. As larvae fed the ALGA, rotifers partially retroconverted DPA to AA in their tissues, the final survival (31.0%) in these larvae was markedly better ( P P Artemia . The results suggest that dietary AA fed prior to handling stress improved survival more effectively than when fed following handling stress. These findings imply, as well, the importance of early larval nutrition on later larval and juvenile survival during crowding, grading and other handling stressors.

Advances in the development of microdiets for gilthead seabream, Sparus aurata : a review

The performance of microdiets (MDs) for larvae of marine fish is frequently improved when they are co-fed with Artemia. This suggests that nutritional factors in the live food are positively influencing the ingestion, digestion and assimilation of the MD. This paper reviews recent advances in MD development on the gilthead seabream with special emphasis on studies that isolated, identified and tested these live food factors in MD with the aim of improving their performance. MD ingestion rates in gilthead seabream larvae increased up to 120% when the fish were exposed to the visual and chemical stimuli of various concentrations of Artemia nauplii. The free amino acids (FAA) alanine, glycine and arginine and the compound betaine were identified from the Artemia rearing medium as metabolites, which stimulated this larval response. Similarly, MD supplemented with phospholipids (PL), particularly phosphatidylcholine (PC), stimulated feeding activity and was consumed up to 45% better in young larval seabream. Moreover, dietary PC appears to have in parallel and/or in tandem a postprandial enhancing effect on lipoprotein synthesis, resulting in improved transport of dietary lipids from the mucosa of the digestive tract to the body tissues. Live food may also contribute exogenous enzymes to the digestion process or provide factors that stimulate larval pancreatic secretions or activate gut zymogens. Seabream larvae ingesting MD supplemented with porcine pancreatic extract (0.05% DW diet) showed a 30% increase in assimilation and demonstrated significantly (P<0.05) improved growth. Older seabream larvae showed 6.75 times more radioactivity in tissue lipids when fed 14C-triacylglycerol (TAG)-labeled MD supplemented with porcine lipase, while younger larvae demonstrated no improved assimilation. Factors in live Artemia may influence digestion by stimulating an endocrine response. This was shown when Artemia consumed by seabream larvae elicited a 300% increase in the level of the digestive hormone bombesin compared to levels in larvae given only a MD. On the other hand, liposomes containing the FAA methionine ingested by halibut juveniles elicited higher levels of the digestive hormone cholecystokinin (CCK) compared to juveniles ingesting liposomes containing physiological saline or fish extract. These studies suggested that mobilizing the native endocrine factors associated with the feeding and digestive processes could improve MD performance in gilthead seabream and other species by maximizing its utilization.

The effect of dietary arachidonic acid on growth, survival, and cortisol levels in different-age gilthead seabream larvae (Sparus auratus) exposed to handling or daily salinity change

The effect of dietary arachidonic acid (ArA) on survival, growth, and cortisol level in different-age gilthead seabream larvae exposed to handling or daily fluctuating salinity was tested. Premetamorphosing (3–19 DPH) larvae were reared in 400-l V-tanks and fed one of three rotifer treatments containing ArA levels of 1.14, 2.11, or 3.87 mg g−1. At 20 DPH, the larvae were divided into two groups where each larval group was randomly divided over twelve 27-l aquaria (300 larvae per aquarium) and the stress of transfer was defined as an acute stressor. In each set of 12 aquaria, larvae were fed over 12 days three Artemia metanauplii treatments, which were tested in four aquaria per treatment, giving Artemia ArA levels of 0.59, 3.42, or 5.86 mg g−1 dry weight (DW). One set of 12 aquaria received seawater of constant salinity (25‰) and these larvae, exposed only to the stress of transfer, were considered as controls. The other set of 12 aquaria was supplied with seawater with a daily fluctuating salinity from 25‰ to 40‰ and back to 25‰, exposing the larvae to 12 days of salinity change. Another trial was carried out on 30 DPH metamorphosing larvae, which were similarly stocked in the aquaria and tested with the identical Artemia treatments as the premetamorphosing larvae study. A positive correlation was found between increasing dietary ArA level and survival at the end of the study in the control premetamorphosing (20–32 DPH) and metamorphosing (30–42 DPH) larvae (38%, 48.6%, and 77.2%, and 58%, 56.4%, and 90.4%, respectively). On the other hand, premetamorphosing and metamorphosing larvae exposed to salinity change, although exhibiting an increase in survival at the intermediate level of ArA, demonstrated a decrease in survival (55.3%, 60.0%, and 25.8%, and 70%, 83%, and 76%, respectively) when fed the highest ArA level. In the control metamorphosing larvae, basal cortisol (6.0, 8.2, and 11.4 ng g−1 DW) was independent of dietary ArA while fish exposed to salinity change demonstrated distinctly higher basal cortisol levels (7.5, 15.9, and 19.8 ng g−1 DW) that markedly increased with rising dietary ArA levels at 42 DPH. Fish exposed to salinity change and fed Artemia containing 0.59, 3.42, and 5.86 mg g−1 ArA exhibited significantly (P<0.05) decreasing SGR values (12.15, 10.68, and 9.69, respectively) while the SGR values in the control larvae (10.23, 10.92, and 9.79, respectively) were generally stable. The results showed that dietary ArA promoted survival in fish encountering only handling stress. In contrast, repetitive salinity change altered the nature of the stress response where dietary ArA appeared to upregulate cortisol synthesis coinciding with reduced growth and increased mortality.

The effects of photoperiod and water exchange rate on growth and survival of gilthead sea bream (Sparus aurata, Linnaeus; Sparidae) from hatching to metamorphosis in mass rearing systems

The effects of photoperiod and water exchange rate on the larvae of gilthead sea bream, Sparus aurata, from hatching to metamorphosis, 60–70 days later, were tested. Survival, growth rate and condition factor were determined with photoperiods of 12 and 24 h, and water exchange rates of 0 and 25%/day. Continuous light supported the highest mean survival (3.25%), with a maximum of 7.8% from hatching to metamorphosis. Growth rate in dry weight was best under continuous light in a water system with no exchange, up to 20 days post-hatching. Highest growth rates of larvae 40–60 days old were obtained in tanks with 25% of their water exchanged daily, along with a 12-h photoperiod. Condition factor was directly correlated with larval age. For the first 30 days after hatching, condition factor was affected by photoperiod and was highest for larvae exposed to continuous light.

Utilisation of yolk fuels in developing eggs and larvae of European sea bass (Dicentrarchus labrax)

Abstract Developing eggs and larvae of European sea bass ( Dicentrarchus labrax ) maintained in filtered sea water (40 gl −1 ) at 18°C, were measured for oxygen uptake, contents of free amino acids (FAA), protein, fatty acids (FA), and volumes of yolk-sac and oil globule. Newly spawned eggs had a dry weight of 90 μ g egg −1 and an egg diameter of 1.14±0.03 mm. The yolk was quickly absorbed during the embryonic and the early larval stages and was 95% depleted by 100 h post fertilisation. The depletion rates of the FAA were somewhat faster than the rate of absorption of the general yolk matter and were almost complete by 80 h post fertilisation. The oil globule was mainly absorbed after hatching following yolk absorption, and occurred concurrently with catabolism of FA from neutral lipids. Approximately 30% of the oil globule was still present at the presumed onset of exogenous feeding. Overall, FAA appeared to be a significant energy substrate during the egg stage and the early yolk-sac stage while FA from neutral lipids derived from the oil globule seemed to be the main metabolic fuel after hatching. Amino acids from protein seemed to be mobilised for energy in the last part of the yolk-sac stage. This investigation supports accumulating evidence for a common sequence of catabolic substrate oxidation in marine pelagic fish eggs that contain oil globules.

THE EFFECT OF SALINITY ON GROWTH RATE, SURVIVAL AND SWIMBLADDER INFLATION IN GILTHEAD SEABREAM, SPARUS AURATA, LARVAE

Abstract The effects of salinity (15–40 p.p.t. salinity; 450–1200 mOsm kg−1) on growth, survival and swim bladder (SB) inflation in gilthead seabream, Sparus aurata, were evaluated. Over the salinity range tested, 1–32 day old seabream larvae were found to be osmotic regulators. Within the range tested, 1 day old larvae maintained an osmotic pressure of 224 mOsm kg−1, significantly lower than 410 mOsm kg−1 in 13 and 24 day old larvae. In addition, water content in larvae was negatively correlated with age, being over 86% in 4 day old larvae and 83% in 32 day old larvae. A negative relationship was found between salinity and survival; as the rearing salinity decreased from 40 to 25 p.p.t., survival increased from 5.3 to 18.6%. Larval final dry weight (DW) and wet weight (WW) were over 16% higher at 25 than 40 p.p.t. salinity. Finally, reduced salinity induced a significant increase in the rate of SB inflation; 65 to 92.5% in 40 and 25 p.p.t. acclimated larvae, respectively.

The effect of dietary phosphatidylcholine on the assimilation and distribution of ingested free oleic acid (18:1n−9) in gilthead seabream (Sparus aurata) larvae

Abstract Two separate studies investigated the effect of dietary phosphatidylcholine (PC) on the assimilation of ingested free fatty acid (FFA) into the tissues of 28-day-old gilthead seabream larvae. Two squid meal based microdiets (MD), labeled with free [1- 14 C] 18:1 n −9, were prepared that were identical in their nonlipid fractions and total lipid levels but differed in their lipid compositions. The control MD contained, by dry weight (DW), 10% capelin oil while the treatment MD comprised of 7.5% capelin oil and 2.5% di-stearylphosphatidylcholine. In the first study, the MDs were fed to seabream larvae over 14 h followed by 10 h of food deprivation in the dark. Larval samples were taken after 1, 8, 14 and 24 h and the resultant distribution of radioactivity in whole body lipid fractions was determined. Starting at 8 h and reaching a maximum after 14 h of feeding, larvae fed the PC diet demonstrated higher ( P −1 , respectively) and free fatty acid fractions (460±66 and 201±40 dpm larva −1 , respectively). This suggested that both the assimilation and ingestion rate in the PC larvae increased over the control fish after 8 h of feeding. During the 10 h of food deprivation, radioactivity in the triacylglycerol (TAG) fraction of the PC larvae decreased by 37% while radioactivity in the control fish TAG decreased by only 16%. Apparently, a considerable amount of this 14 C-label was mobilized for membrane lipid synthesis as evidenced by increases of 14 C-label in the PL class of the PC and control larvae that reached 1447±62 and 737±49 dpm larva −1 , respectively. The second experiment examined the influence of dietary PC on the mobilization of ingested 14 C-oleic acid from the digestive tract to the body. The levels of 14 C-label in the PL, TAG and cholesterol ester (CE) lipid classes in the body were significantly ( P −1 , respectively) compared to fish ingesting the control treatment (85±32, 26±12 and 36±33 dpm larva −1 , respectively). Conversely, control larvae exhibited 57% (141±41 dpm larva −1 ) of its 14 C-label in the TAG fraction of the gut while PC larva only accumulated 14% (15±11 dpm larva −1 ) of their total 14 C-label in this region. The results clearly suggest that PC fed larvae, compared to the PC deficient control, were more rapidly transporting dietary FFA to the tissues as evidenced by their accumulating levels of radioactivity in the PL class of the body as feeding continued.