Interactions between dietary docosahexaenoic acid and other long-chain polyunsaturated fatty acids on performance and fatty acid retention in post-smolt Atlantic salmon (Salmo salar)

A study with varying dietary inclusion levels (1, 5, 10, 15 and 20 g kg-1) of docosahexaenoic acid (DHA; 22:6n-3) was conducted with post-smolt (111 ± 2.6 g; mean ± S.) Atlantic salmon (Salmo salar) over a 9-week period. In addition to the series of DHA inclusion levels, the study included further diets that had DHA at 10 g kg-1 in combination with either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), both also included at 10 g kg-1. An additional treatment with both EPA and DHA included at 5 g kg-1 (total of 10 g kg-1 long-chain polyunsaturated fatty acids, LC-PUFA) was also included. After a 9-week feeding period, fish were weighed, and carcass, blood and tissue samples collected. A minor improvement in growth was seen with increasing inclusion of DHA. However, the addition of EPA further improved growth response while addition of ARA had no effect on growth. As with most lipid studies, the fatty acid composition of the whole body lipids generally reflected that of the diets. However, there were notable exceptions to this, and these implicate some interactions among the different LC-PUFA in terms of the fatty acid bio- chemistry in this species. At very low inclusion levels, DHA retention was substantially higher (*250 %) than that at all other inclusion levels (31–58 %). The inclusion of EPA in the diet also had a positive effect on the retention efficiency of DHA. However, EPA retention was highly variable and at low DHA inclusion levels there was a net loss of EPA as this fatty acid was most likely elongated to produce DHA, consistent with increased DHA retention with addi- tional EPA in the diet. Retention of DPA (22:5n-3) was high at low levels of DHA, but diminished with increasing DHA inclusion, similar to that seen with DHA retention. The addition of EPA to the diet resulted in a substantial increase in the efficiency of DPA retention; the inclusion of ARA had the opposite effect. Retention of ARA was unaffected by DHA inclusion, but the addition of either EPA or ARA to the diet resulted in a substantial reduction in the efficiency of ARA retention. No effects of dietary treatment were noted on the retention of either linolenic (18:3n-3) or linoleic (18:2n-6) acids. When the total n-3 LC-PUFA content of the diet was the same but consisted of either DHA alone or as a combination of EPA plus DHA, the performance effects were similar

A Study on the Factors Influencing the Growth and Survival of Juvenile Sea Cucumber, Holothuria atra, under Laboratory Conditions

In recent years the sea cucumber fishery has emerged as a lucrative business in Mauritius. However, few studies on these marine detritivorous animals have been carried out in the island either in the wild or for aquaculture. The aim of the present study was to investigate the influence environmental factors such as salinity and temperature and biological factors such as stocking density and feed type on the growth and survival of juvenile sea cucumbers Holothuria atra. The study was conducted from mid-October 2006 to end of January 2007 period. For the experiment, 150 juvenile H. atra of similar size and weighing (27-30 g) were collected from Le Morne and Albion Lagoons. The experiments were carried out in round polyether tanks of 2 m3 with an area of 1.5 m2 at Albion Fisheries Research Centre. The juveniles H. atra (6 specimens per tank in duplicate) were reared at salinity 25, 30 and 35 ppt; temperature 26, 28 and 32°C; and were given two feed types (crushed algae and a formulated feed (85% crushed algae and 15% fish feed)). For studying stocking density duplicate tanks containing 6, 12 and 18 specimen (per sq m) were used. At one-week intervals, the sea cucumbers were starved for 24h and then weighed. The wet weight was used as an index for its growth performance over the experimental period. The highest specific growth rate (SGR) and survival were obtained at temperature of 28°C (1.43 ± 0.15 g and 100% respectively). At temperature 32°C, the SGR was a lower (0.78 ± 0.12 g) and a survival of 67%. Specific growth rate and survival was lowest in stocking density 18 (0.12 ± 0.23 g & 69% respectively). At salinity of 25 ppt there was decrease in SGR during the experimental period (-4.61 ± 0.29 g). Feeding H. atra with crushed algae produced little increase in growth (0.18 ± 0.16 g) while feeding with formulated feed the specific growth rate was notable (0.97 ± 0.14 g). Under the conditions of the experiments, growth and survival of juvenile H.atra were greatest at 35‰ salinity, temperature 28ºC, and a formulated feed made from algae and dried fish feed and density of 6 specimens per m2.Keywords: Holothuria atra; Salinity; Temperature; Stocking density; Feed type; Specific growth rate (SGR); Surviva

Digestible choline requirement of juvenile yellowtail kingfish (Seriola lalandi)

The present study was conducted to determine the digestible choline requirement of juvenile yellowtail kingfish (Seriola lalandi; YTK) in the presence of 2-amino-2-methyl-1-propanol (AMP), an inhibitor of choline biosynthesis. The second aim of this study was to determine if choline supplementation of a practical diet made from common raw materials can improve the growth performance of YTK and if choline supplementation dosages are affected by water temperature. Two eight-week experiments were conducted. The first was a dose-response experiment in which juvenile YTK (156.3 ± 15.3 g) were reared at 16 °C and fed five isonitrogenous and isoenergetic semi-purified diets containing 0.42 (Diet 1), 1.10 (Diet 2), 1.37 (Diet 3), 2.96 (Diet 4) or 6.05 g digestible choline kg−1 diet (Diet 5) by adding graded concentrations of choline chloride (CC). A sixth diet (Diet 6), comparable to Diet 4, was made without AMP to estimate the de novo synthesis of choline by YTK. The second was a factorial experiment in which juvenile YTK (157.3 ± 11.9 g) were reared at 16 °C and 24 °C and fed a practical diet supplemented with 0.0, 3.0 or 6.0 g of CC kg−1 which equates to a digestible choline concentration of 1.77, 3.54 and 4.66 g kg−1 diet, respectively. Results from experiment 1 indicated the breakpoint (broken-line regression model) in specific growth rate (SGR) and choline deposition rate occurred when digestible choline intake reached 26.1 mg kgBW−1 d−1 and 27.3 mg kgBW−1 d−1, respectively. On a dietary basis, the breakpoint in SGR and choline deposition rate occurred when diets provided 1.93 and 1.94 g digestible choline kg−1 diet, respectively. Experiment 2 results indicated there were no significant interactions between dietary choline and water temperature with respect to production indices such as SGR, food conversion ratio (FCR), whole body composition and nutrient retention. Choline deposition rate, SGR and FCR tended to be better in fish fed the practical diet supplemented with 3.0 g CC kg−1, but there was no additional advantage of raising the content to 6.0 g CC kg−1 diet. The present study confirms the necessity of adding CC to practical diets for YTK given that practical diets with no CC supplementation contain lower digestible choline than the estimated requirement established in experiment 1

Effect of Feed Texture and Dimensions, on Feed Waste Type and Feeding Efficiency in Juvenile <i>Sagmariasus verreauxi</i>

The “messy” feeding behaviour of spiny lobsters remains an obstacle for formulated feed development. This study examined the relationship between feeding efficiency and feed waste by juvenile spiny lobster, Sagmariasus verreauxi, fed different formulated pellet diameters or lengths across two separate experiments. Feed texture (hard and dry pellet, HDP; soft and moist pellet, SMP) was also examined. Juvenile lobsters were fed experimental feeds at 0.5% BW daily over a 6 h duration. The resulting feed waste was categorised as either feeding-related waste (FRW) or non-feeding-related waste (NFRW). For all feed types, the FRW increased with increasing pellet diameter and pellet length. The increase in FRW corresponded with a decrease in NFRW, particularly for HDP, resulting in no difference in total feed waste in any treatment investigated. Thus, even with improved feeding efficiency with small feed dimensions, feed intake was not improved. Feed leaching rate decreased with increasing pellet size, suggesting a more rapid decline in feed attractiveness for smaller pellets. This finding indicates that currently a counteractive interaction exists between pellet size and feed attractiveness and suggests improving attractiveness would further enhance feeding. Future research should aim at optimising feed dimensions simultaneously to support efficient feeding whilst enhancing attraction/gustatory stimulations

n-3 LC-PUFA deposition efficiency and appetite regulating hormones are modulated by the dietary lipid source during rainbow trout grow-out and finishing periods

Largely attributable to concerns surrounding sustainability, the utilisation of omega-3 long-chain polyunsaturated fatty acid-rich (n-3 LC-PUFA) fish oils in aquafeeds for farmed fish species is an increasingly concerning issue. Therefore, strategies to maximise the deposition efficiency of these key health beneficial fatty acids are being investigated. The present study examined the effects of four vegetable-based dietary lipid sources (linseed, olive, palm and sunflower oil) on the deposition efficiency of n-3 LC-PUFA and the circulating blood plasma concentrations of the appetite-regulating hormones, leptin and ghrelin, during the grow-out and finishing phases in rainbow trout culture. Minimal detrimental effects were noted in fish performance; however, major modifications were apparent in tissue fatty acid compositions, which generally reflected that of the diet. These modifications diminished somewhat following the fish oil finishing phase, but longer-lasting effects remained evident. The fatty acid composition of the alternative oils was demonstrated to have a modulatory effect on the deposition efficiency of n-3 LC-PUFA and on the key endocrine hormones involved in appetite regulation, growth and feed intake during both the grow-out and finishing phases. In particular, n-6 PUFA (sunflower oil diet) appeared to &lsquo;spare&rsquo; the catabolism of n-3 LC-PUFA and, as such, resulted in the highest retention of these fatty acids, ultimately highlighting new nutritional approaches to maximise the maintenance of the qualitative benefits of fish oils when they are used in feeds for aquaculture species