Enriched Rotifers Research Articles

Performance and skeletal abnormality of striped trumpeter Latris lineata larvae and post larvae fed vitamin A enriched Artemia

Several nutritional studies have found that excess or reduced dietary vitamin A (VA) causes skeletal malformations in marine fish larvae. Feeding VA enriched rotifers to striped trumpeter (Latris lineata) from 6 to 18 days post hatch (dph) has been shown to affect vertebral column malformations but not jaw malformation. Our study examined the effect of dietary VA during the later Artemia feeding period on the prevalence of malformations. Larvae were initially reared in a 3000 l tank and fed a diet of Algamac-3050 enriched rotifers from 2 to 16 dph. At 16 dph, larvae were transferred to 24 × 300 l tanks and fed Artemia enriched with one of six doses of retinyl palmitate (VA) four times per day from 19 to 44 dph. Enrichment with emulsions containing 0 (control), 795, 1558, 3174, 4911 and 10,518 ng retinyl palmitate mg− 1 emulsion resulted in an average VA in Artemia of 0, 6, 7, 27, 30 and 55 ng retinyl palmitate mg− 1 dry weight (DW). The retinoid content of L. lineata at 44 dph was positively correlated with the enriched Artemia they fed on. Growth in length (15.91 ± 0.31 mm, mean ± SD) and dry weight (5.08 ± 0.32 mg), and survival (26.1 ± 2.9%), were not significantly affected at 44 dph by increasing dietary doses of retinyl palmitate. Retinyl palmitate enrichment in Artemia did not affect jaw malformation in L. lineata, which is contrary to other studies on a range of marine fish species treated with increased doses of dietary VA. By the end of the study, 54 ± 10% and 18 ± 6% of the post larvae across treatments had short lower and open jaws, respectively. Severe jaw malformations affected 50 ± 11% of the post larvae. Early culture of larvae in a larger tank was likely to reduce overall prevalence of jaw malformations compared to previous studies as interaction with tank walls was reduced. The prevalence of vertebral column malformations in 44 dph post larvae (58 ± 4%) were also not affected by dietary VA. The study suggests that the window of influence for dietary VA is during earlier development of bone structures in L. lineata.

Rotifers enriched with iodine, copper and manganese had no effect on larval cod (Gadus morhua) growth, mineral status or redox system gene mRNA levels

It currently remains unclear if rotifers contain sufficient mineral levels to meet larval fish requirements. In this study, rotifers were enriched with a commercial enrichment (control), or with additional iodine, iodine and copper, or iodine, copper and manganese, and the effects of feeding these rotifers to Atlantic cod (Gadus morhua) larvae from 3 to 18 days post hatch were investigated. Rotifer enrichment with minerals was successful, but Mn enrichment also increased rotifer zinc levels. No differences were observed between treatments in larval growth or survival, or in the mRNA levels in the majority of the redox system genes analysed. Only Zn levels increased in cod larvae in response to mineral enrichment of rotifers. Apart from Zn, little evidence was found to suggest that cod larvae require increased concentrations above the control rotifer levels of the essential elements studied here.

Morphological and Genetic Identification of Spontaneously Spawned Larvae of Captive Bluefin Tuna in the Adriatic Sea

ABSTRACTThe spawning behavior of captive Bluefin Tuna (Thunnus thynnus) was observed in cages at an Adriatic facility in summer 2011. Approximately 20,000 eggs were collected from cages and transferred to a land‐based nursery, with an estimated fertilization success rate of 80%. Eggs were spherical with a diameter of 1,035.06 ± 20.16 μm and were pelagic with a single oil globule (227.63 ± 8.07 μm). Newly hatched larvae (3.08 ± 0.14 mm total length) followed scombrid larval development: melanophores were scattered over the body, head, notochord, and yolk, except finfold; eye pigmentation was observed 1.5 days posthatch, pectoral fins started to appear, and two‐thirds of the yolk sac were absorbed; the mouth developed at 2.5 days posthatch, and larvae began feeding upon enriched rotifers. After mortalities occurred in the nursery (5 days posthatch), DNA was extracted from a sample of larvae. An 890 base pair fragment of the mitochondrial partial control region was amplified and sequenced to genetically confirm fish species identity. Based on multiple sequence alignment, larval sequences showed no ambiguities to the T. thynnus mitochondrial control region, thereby confirming spontaneous spawning in captivity. Although such an event has previously been reported in the Mediterranean, this is the first report supported by both morphological and genetic data.

Effect of feeding rotifers enriched with taurine on the growth and survival of larval amberjack Seriola dumerili

The effect of feeding rotifers enriched with taurine on the growth performance and survival of larval amberjack Seriola dumerili was investigated. Rotifers were enriched with a commercial taurine supplement at four levels (0, 200, 400, and 800 mg/l). The larvae were fed the enriched rotifers in triplicate from 3 days post-hatch for 7 days under static conditions. The average taurine contents of the rotifers were 1.5, 2.7, 4.2, and 7.2 mg/g dry matter, respectively. The growth of the fish fed rotifers enriched with the taurine supplement at 800 mg/l was significantly (P < 0.05) improved compared with that of the fish fed the rotifers without taurine enrichment. The survival rate improved proportionally up to a taurine supplement level of 400 mg/l, but no significant differences in survival were observed among treatments. The fraction of the larvae with inflated swim bladders did not vary significantly between treatments. Taurine content in the whole fish body increased with the taurine level in the rotifers. These results suggest that taurine enrichment of rotifers is an effective method of enhancing the growth of amberjack larvae.

LIFE-FEED ENRICHMENT FOR LARVAL REARING OF YELLOWBAND CLOWNFISH (Premnas biaculeatus)

The seeds of yellowband clownfish from hatchery has a pale skin colour and a yellow stripe became white colour. The purposes of this research were to know the effects of life-feed enrichment on the growth of larva and the appearance of colors yellowband clownfish. The treatments were the enrichment of rotifers and Artemia with commercial enrichment + Nannochloropsis (A), and without commercial enrichment as control, only Nannochloropsis (B). This research conducted for 15 days rearing. Larva rearings of yellowband clownfish fish with treatment A were resulted the total length at the end experiment was 7.72 ± 0.63 mm, dan survival rate 52.6 ± 19.1 %. The total length at treatment B was 7. 61 ± 0.43 mm and survival rate 47.7 ± 24.2%. Different enrichment of life-feed was not significant different effect for total length, survival rate and colour of seeds Keywords: life-feed, enrichment, growth, survival rate, colour, yellowband clownfish.

LIFE-FEED ENRICHMENT FOR LARVAL REARING OF YELLOWBAND CLOWNFISH (Premnas biaculeatus)

&lt;p&gt;The seeds of yellowband clownfish from hatchery has a pale skin colour and a yellow stripe became white colour. The purposes of this research were to know the effects of life-feed enrichment on the growth of larva and the appearance of colors yellowband clownfish. The treatments were the enrichment of rotifers and Artemia with commercial enrichment + Nannochloropsis (A), and without commercial enrichment as control, only Nannochloropsis (B). This research conducted for 15 days rearing. Larva rearings of yellowband clownfish fish with treatment A were resulted the total length at the end experiment was 7.72 ± 0.63 mm, dan survival rate 52.6 ± 19.1 %. The total length at treatment B was 7. 61 ± 0.43 mm and survival rate 47.7 ± 24.2%. Different enrichment of life-feed was not significant different effect for total length, survival rate and colour of seeds&lt;/p&gt; &lt;p&gt;Keywords: life-feed, enrichment, growth, survival rate, colour, yellowband clownfish.&lt;/p&gt;

The Effects of Different Feed Enrichments on Survivorship and Growth of Early Juvenile Longsnout Seahorse, Hippocampus reidi

AbstractCulturing the longsnout seahorse, Hippocampus reidi, remains challenging because unlike most cultured seahorse species, Artemia is not an optimal first feed. Ideally, more nutritious live feeds such as wild plankton or copepods should be used, but are not always readily available. Therefore, facilities commonly utilize enriched rotifers. Numerous feed enrichment products exist, including Dan's Feed Artemia Enrichment®, (Dan's Feed) which is a blend of commercially available enrichment products. The aim of this study was to assess the survivorship, growth, and condition factor (CF) of 0–28 DPR (days post release) H. reidi fed with rotifers and Artemia enriched with Dan's Feed. This enrichment was evaluated against (1) rotifers and Artemia enriched with live alga (Isochrysis galbana), and (2) wild plankton and Artemia enriched with Dan's Feed. At 28 DPR, in terms of survivorship and growth, seahorses fed with rotifers and Artemia enriched with Dan's Feed had a lower CF and outperformed those fed rotifers and Artemia enriched with I. galbana. Seahorses fed with rotifers and Artemia enriched with Dan's Feed performed on par with those fed with wild plankton and Artemia with no significant difference in CF. These findings demonstrated that the culture of H. reidi may be feasible with rotifers and Artemia enriched with Dan's Feed.

The effects of dietary vitamin A in rotifers on the performance and skeletal abnormality of striped trumpeter Latris lineata larvae and post larvae

Several nutritional studies have linked dietary vitamin A (VA) to skeletogenesis in marine fish larvae. In our study, rotifers were enriched with eight levels of retinyl palmitate. Striped trumpeter (Latris lineata) larvae were fed rotifers twice daily, VA-enriched rotifers (morning feed) and Algamac−3050 enriched rotifers (afternoon feed), in greenwater systems from 6 to 18days post-hatch (dph). The VA-enriched rotifers had incorporated 0, 6, 14, 26, 57, 109, 215 and 388ng retinyl palmitatemg−1 dry weight (DW) following 2h enrichment with emulsions containing 0 (control), 68, 187, 532, 1402, 2670, 4808 and 9523ng retinyl palmitatemg−1 emulsion. After the rotifer feeding phase (6 to 18dph), the larvae were fed Algamac−3050 enriched Artemia until 43dph. The pattern of increasing VA in the enriched rotifers was not reflected in the larvae. Larvae incorporated 11.08±0.27ng total retinolmg−1 DW (mean±SD) when fed rotifers containing 0.93 to 2.32ng total retinolmg−1 DW (6 to 14ng retinyl palmitatemg−1 DW) and incorporated a lower level of 5.57±0.30ng total retinolmg−1 DW when fed rotifers with 0.52 (control) or ≥16.31ng total retinolmg−1 DW (0 and ≥57ng retinyl palmitatemg−1 DW). By 43dph, neither larval growth in length (16.0±0.1mm) or dry weight (4.57±0.20mg), nor survival (34.8±10.6%), were significantly affected by increasing dietary levels of retinyl palmitate. The prevalence of vertebral column malformations in 43dph post larvae was positively correlated with total retinol content of larvae at 16dph (R2=0.55, P<0.001). Unlike other studies on a range of marine fish species, retinyl palmitate enrichment in rotifers did not affect the type or severity of jaw malformations. By 43dph, 81±9% of post larvae displayed severe jaw malformations. Vitamin A daily inclusion of more than 123ng total VAmg−1 DW rotifer, equivalent to more than 35ng total retinol mg−1 DW rotifer (109ng retinyl palmitatemg−1 DW rotifers), is recommended to reduce vertebral column malformations when L. lineata larvae are reared in greenwater.

Examination of a practical method for copper enrichment of euryhaline rotifers (Brachionus plicatilis) as diet ofEriocheir sinensiszoea larvae

In this study, an effective method to enrich the rotifer Brachionus plicatilis with copper was developed as a feed for the Chinese mitten crab Eriocheir sinensis zoea larvae. Changes in the concentrations of other minerals in rotifers were also examined when copper was added for rotifer enrichment. The ability of Chlorella to absorb waterborne copper is much higher than that of rotifers, and hence, copper was preaccumulated in Chlorella before its ingestion by rotifers. The copper content in rotifers was comparable to the dietary copper requirement of the crab larvae when the rotifers were enriched with 0.1 mg Cu g−1 Chlorella for 12 h. Further enrichment in rotifers with Cu-enriched Chlorella and lipid emulsions did not significantly change the profile of major fatty acids and mineral composition in the rotifers. Evidence shows the feasibility of copper enrichment in rotifers using microalgae that can accumulate copper. This study indicates that copper in rotifers can be enriched by feeding copper-enriched algae at a concentration of 0.1–0.2 mg Cu g−1 Chlorella. The developmental rates of E. sinensis can be improved by feeding zoea larvae with copper-enriched rotifers, but survival rates were not affected by dietary copper enrichment.

Increasing the levels of the essential trace elements Se, Zn, Cu and Mn in rotifers (Brachionus plicatilis) used as live feed

Rotifers are a common first feeding diet for rearing marine fish larvae. However, the levels of Mn, Cu, Zn, Se and iodine found in rotifers are low and may be insufficient to meet larval fish requirements. This study investigates increasing the concentration of Mn, Cu, Zn, Se and iodine simultaneously in rotifers (Brachionus plicatilis) in both short term enrichments (3h) or during batch cultures (6days), using either organically bound or inorganic mineral sources. This study demonstrates that rotifers can simultaneously be produced with Mn, Cu, Zn and Se concentrations up to and higher than the known requirements of fish, while increasing the level of iodine in rotifers was ineffective at the concentrations tested. To produce rotifers with copepod levels of Mn, Cu, Zn and Se, only 6% of a commercial rotifer enrichment diet had to be replaced with organically bound minerals, leaving a large percentage of the rotifer diet free to deliver other important nutrients such as lipid and proteins. Rotifers enriched to copepod mineral levels and stored for 18h retained 75–110% of their Se, Zn and Mn and 50% of their Cu. Overall, increasing rotifer mineral levels appears to be most effective when the mineral is available in an insoluble and hence ingestible form.

Replacement of fresh algae with commercial formulas to enrich rotifers in larval rearing of yellowtail kingfishSeriola lalandi(Valenciennes, 1833)

This study compared the efficacy of four products that are commonly used in hatchery for nutritional enhancement of rotifer Brachionus plicatilis as the starter food for yellowtail kingfish Seriola lalandi larvae. This experiment consisted of one fresh algae and three enrichment products: (1) Fresh algae were a mixture of Nannochloropsis and Isochrysis at 2:1 on a cell concentration basis; (2) S.presso, (Selco S.presso ®, INVE Aquaculture); (3) Algamac 3050® (Aquafauna, USA); (4) Nutrokol ® (Nutra-Kol, Australia). Survival rates of the fish fed rotifers enriched with fresh microalgae (40.69%) and S.presso (31.21%) were higher than those fed Algamac 3050 (10.31%). On 3 day post hatch (DPH), fish feeding incidence in the fresh algae treatment was significantly higher than that in other treatments. On 6 DPH, fish showed the lowest feeding incidence in the Algamac 3050 treatment. The methods of enrichment did not affect total lipid levels in either rotifer or fish larvae, but Algamac 3050 enrichment achieved the highest DHA/EPA ratio and lowest EPA/ARA ratio in both rotifers and fish larvae. This study indicates that fresh algae can be replaced by S.presso, but Algamac 3050 is not as good as other formula for rotifer enrichment in rearing yellowtail kingfish larvae in this system.

AreAcartia tonsacold-stored eggs a suitable food source for the marine ornamental speciesAmphiprion polymnus? A feeding study

Copepods are the natural food items for marine fish larvae but are still difficult to be cultured on a continuous basis. Therefore, suitable storage techniques for copepod subitaneous eggs are of great interest. Cold-stored copepod embryos still develop and retain a physiological activity during the cold storage period. As a consequence, their nutritional quality may change over the time of storage with these changes possibly affecting both eggs viability and larval fish survival and development. In this study, the clownfish, Amphiprion polymnus, was used as an experimental model to compare, for the first time, the effects of diets based on enriched rotifers and Artemia (control), Acartia tonsa copepods of a continuous culture and A. tonsa originated from 6 months cold-stored eggs. The effects of the different diets were tested through morphometric, molecular and biochemical approach. This study demonstrated that after a 6 months cold storage period, the quality of copepods obtained from those eggs was suboptimal for A. polymnus larval rearing. In fact, larvae fed those copepods showed lower growth and survival performances respect to the other experimental groups.

Effect of different algae used for enrichment of rotifers on growth, survival, and swim bladder inflation of larval amberjack Seriola dumerili

The effect of algae with different DHA contents used for the enrichment of rotifers on the growth performance, survival, and swim bladder inflation of larval amberjack Seriola dumerili was investigated. Rotifers were enriched with freshwater Chlorella vulgaris containing three levels of DHA (rotifer containing DHA 0.04, 0.60, 1.32 g DHA 100 g−1 DM) and Nannochloropsis (0.04 g DHA 100 g−1 DM; 2.54 g EPA 100 g−1DM). The larvae were fed the enriched rotifers in triplicate from 3 days post-hatch for 7 days in static condition. The same algae used for rotifer enrichment were supplied to the larval tanks. Growth and survival rate of fish fed the rotifers enriched with Nannochloropsis were higher than those of fish fed the rotifers enriched with all three Chlorella treatments. Swim bladder inflation was lowest in fish fed the rotifers enriched with Nannochloropsis. The proportion of EPA was higher in fish fed the rotifers enriched with Nannochloropsis, while that of DHA increased proportionally with the DHA levels in the rotifers enriched with Chlorella. These results suggest that rotifers enriched with Nannochloropsis (EPA-rich rotifers) are effective to enhance growth and survival, but DHA instead of EPA is essential to improve the swim bladder inflation in amberjack larvae.

Nucleotide Enrichment of Live Feed: A Promising Protocol for Rearing of Atlantic Cod Gadus morhua Larvae

We investigated the effect of two commercial nucleotide products (NT1 and NT2), administered through live feed, on growth and stress tolerance of Atlantic cod larvae. Expression of genes related to muscle growth (igf-1, igf1r, igf-2, fst, fgf6, myod, and myhc) and nucleotide metabolism (uox, hprt, ndk, and uck) was evaluated during larval development. In addition, the expression of genes related to stress (hif-1α, hif-2α, hif-3α, and mb) was studied after an air exposure stress test. The enrichment of rotifers with nucleotides did not reveal any difference in nucleotide profiles, the exception being the RNA level of the NT1-enriched group that was significantly higher than the unenriched rotifer. Unenriched Artemia showed poor nucleotide profiles compared to enriched Artemia since 5' UMP, 5' GMP, and 5' AMP were observed only in the nucleotide groups. At 38days post-hatch (dph), NT1 group had significantly higher dry weight (3.1 ± 0.1mg) than the control (CON; 2.3 ± 0.1mg). The treatments did not produce any significant differences in the expression of the key myogenic genes. Among the genes associated with nucleotide metabolism, ndk was down-regulated in NT1 at 38 dph. In the air exposure test, survival was significantly higher in the CON (77 ± 6%) than in NT1 (48 ± 3%) and NT2 (50 ± 3%). After air exposure, mb was expressed at lower levels in NT2 group, hif-2α was induced in NT1 group, and hif-3α was upregulated in all groups. Our findings indicate that the improvement in the nucleotide profile of Artemia upon nucleotide enrichment could eventuate in the rapid growth of larvae.

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.

Lutein enrichment of the rotifer Brachionus sp. using freeze-dried Muriellopsis sp. cells

Rotifers, used in aquaculture as feed for early larval stages, are poor in carotenoids compared with copepods, the natural most common prey item of marine fish larvae. A minimal sufficient level of carotenoids in fish larvae may be essential for a correct development. The freshwater microalga Muriellopsis sp. has been identified as a potential source of the carotenoid lutein with possible application in aquaculture. Lutein is a potent antioxidant, with potentially beneficial effects as a carotenoid for fish larvae. This study describes the lutein enrichment of the rotifer Brachionus sp. when incubated with homogeneously dispersed suspensions of freeze-dried, lutein-rich Muriellopsis sp. in seawater. A short enrichment time (2 or 2.5 h) resulted in a higher lutein content of the rotifers than a long enrichment time (13.5 or 24 h). Although the concentration of lutein in enriched rotifers, 0.06–0.16 mg (g dry weight)−1 was low compared with its content in Muriellopsis sp. [about 3 mg (g dry weight)−1], it was in the range reported for natural copepod populations. Therefore, we conclude that freeze-dried biomass of Muriellopsis sp. can be used to enrich rotifers with lutein, providing an adequate level of this carotenoid for marine fish larvae.

Stress Survival in Larvae of Florida Pompano (Trachinotus carolinus) Fed Enriched Rotifers (Brachionus plicatilis) and Nauplii of the Calanoid Copepod (Pseudodiaptomus pelagicus)

The Florida pompano, Trachinotus carolinus, is a highly prized marine fish whose larviculture includes the feeding of live rotifers and brine shrimp nauplii. In a previous study, growth and survival of pompano larvae fed nauplii of the calanoid copepod, Pseudodiaptomus pelagicus, were compared to those of larvae fed enriched rotifers, Brachionus plicatilis. There were advantages to including the copepod in the larvae diet. The current study examines the stress tolerance of such larvae. Two trials were conducted: for seven (trial 1) and nine (trial 2) days post-hatch. Larvae were fed diets that included enriched rotifers and/or P. pelagicus nauplii and subjected to varying durations of air exposure (‘sieve stress’). Larvae fed copepods exhibited significantly greater stress tolerance than larvae fed only enriched rotifers. In trial 1, stress tolerance increased as the number of days on which copepods were fed increased. It is possible that stress tolerance improved because of a better nutritional profile of the copepod nauplii.

The potential inhibitory effects of the commercial diets on protease activities of Dentex dentex larvae and live foods

The aim of this study was to determine the potential inhibitory effects of commercial diets on protease activities of Dentex dentex larvae and live foods. The highest and lowest protease ac-tivity of larvae was 387.08 ±0.23 U/mg protein and 54.66 ±0.15 U/mg protein, respectively. The highest and lowest protease activities of live foods were found in Artemia metanaupli (414.5 ±0.41 U/mg protein) and rotifer (156.25 ±0.09 U/mg protein), respectively. The signifi-cant differences between inhibition amounts of commercial diets on protease activities of lar-vae and live foods were found (p0.05). Also, the significant differences between the inhibi-tion percents were observed (p0.05). The highest inhibition percents of Caviar (200-300μ), Caviar (300-500μ) and copeod were found as 91.86 ±0.26%, 90.72 ±0.13% and 90.82 ±0.22% in enriched rotifers, respectively. In addition, the highest inhibition percents of Caviar (100-200μ) and Proton (200-400μ) were observed as 93.57 ±0.18% and 93.34 ±0.22% in the larvae on day 35, respectively. The effect of Caviar (200-300μ) on protease activities of rotifer was the lowest. In general, copepod had the lower inhibitory effect han those of other com-mercial diets on protease activities of larvae. Copepod showed the lowest effect on protease activity of larvae on day 30. The inhibition percents of commercial diets on protease activities of live foods were high except for rotifers. Our study revealed that the inhibitory effects of commercial diets used through weaning on protease activities of larvae and live foods should be taken into account. In conclusion, the potential inhibitory effects of commercial diets on protease activities of marine fish larvae and live foods to increase the survival and growth rates in hatcheries should be investigated in future studies.

A study on enrichment of the rotifer Brachionus “Cayman” with iodine from different sources

Iodine is an important micronutrient for the marine fish metamorphosis and rotifers contain relatively low amounts of iodine compared to copepods, the main natural prey for marine fish larvae. In previous studies, rotifers were enriched with iodine from NaI. However, this source of iodine is poorly retained in rotifers during storage. In the present study rotifers were enriched (3h) with graded levels of thymol iodide (TI), 3-5-diiodosalicylic acid (DISA), chelated iodine (CI), kelp and sodium iodide (NaI) mixed with a commercial enrichment diet (Ori-green®). Thereafter, iodine retention in rotifers enriched with selected iodine sources and concentration and stored (0, 1, 2, 5, 10 and 18h) at high and low temperatures was studied (room temperatures at 24 and 7°C, respectively).Linear regression showed a positive relationship between dietary and rotifer iodine concentration for all iodine sources. Results from the first trial showed that 0.36–2.03% replacement of the enrichment diet with TI, gave copepod iodine levels. Maximum iodine level (446.67mgkg−1DW) was observed in the rotifers fed with a diet containing 9.7gkg−1 rotifer DW, added iodine from TI. 118mgkg−1DW iodine was observed in rotifers fed with diet containing 9.7gkg−1 rotifer DW, added iodine from DISA. Rotifers enriched with kelp, gained maximum up to 196mgkg−1DW iodine in this study. Chelated iodine was a poor source of iodine for rotifer enrichment. Even with 100% replacement of the enrichment diet with CI, rotifers were not able to reach the lower copepod iodine level (50mgkg−1DW). 0.3gl−1 NaI gave 370mgkg−1DW iodine in rotifers. Trial 1 indicated that with TI, DISA and NaI, rotifers can be enriched to copepod level with minimal replacement of the enrichment diet.In trial 2, temperature did not affect the rotifer iodine retention. In the first h of storage, rotifer enriched with TI lost 34–62% iodine and rotifers enriched with DISA lost 55–66% iodine while NaI enriched rotifers lost 78–85% iodine. After 18h storage 79–97% loss was observed in rotifers enriched with NaI and 40–56% loss was observed in rotifers enriched with TI. Loss of the other compounds was intermediate.In conclusion, thymol iodide seems to be a good source of iodine for enrichment of rotifers as only <2.5% replacement of the enrichment diet gives copepod iodine levels and after enrichment followed by storage at high or low temperature for 18h, rotifers are able to retain relatively high amounts of iodine in their body.

Pepsin ontogeny and stomach development in larval cobia

The appearance of stomach pepsin activity in teleosts is one of the last ontogenetic events during the larval stages, and typically marks the completion of the shift from intracellular to extracellular mode of digestion. The present trial describes the morphological and functional ontogeny of cobia's stomach. Larvae were reared in a recirculated system and fed enriched rotifers in green water, followed by enriched Artemia, prior to being weaned on an artificial diet 25 days-post-hatch (dph). The stomach commenced differentiation at 6 dph, and displayed numerous gastric glands by 16 dph (11.1 mm TL). However, pepsin-like activity was not detectable prior to 22 dph (20.8 mm TL, P < 0.05), denoting a lack of functionality until this time point. Maximum pepsin-like activity reached 29.09 ± 1.47 U Hb larvae − 1 . Together with the observations of others, the results presented herein shed light on the ontogeny of proteolitic digestion in cobia.