The effect of dietary docosahexaenoic acid (DHA; 22:6n-3) on photoreceptor abundance, rhodopsin expression and growth in developing gilthead sea bream (<em>Sparus aurata</em>) larvae

This study determined the effect of prey DHA on larval gilthead sea bream (GSB; Sparus aurata) photoreceptor abundance, rhodopsin expression, and growth performance. It was carried out in a twenty-eight 400 l conical tank system that was stocked with 100 viable GSB eggs/l/tank. This allowed the testing of 4 levels of rotifer DHA; 0.99 (Low; L), 1.9 (Intermediate low; I-L), 3.2 (Intermediate high; I-H) and 12.1(High; H) mg DHA/g DW rotifer, which were fed (10 rotifers/ml) to 3-16 DPH larvae. These rotifer diets continued to be offered to 17-34 DPH fish, although these larvae predominantly fed on 4 DHA enriched Artemia nauplii treatments that were offered at a concentration from 0.1 nauplii/ml to 4 nauplii/ml, depending on larval age. This resulted in 4 DHA rotifer-Artemia ranges: 0.99-0.0 (L), 1.9-2.6 (I-L), 3.2-7.2 (I-H), and 12.1-11.77 (H) mg DHA/g DW. The 4 DHA treatments and ranges were tested in replicates of 7 conical tanks per treatment. Increasing rotifer DHA significantly (P<0.0001) improved TL, in an exponential manner, throughout larval rearing. DW in 34 DPH larvae was markedly (P<0.05) enhanced with dietary DHA inclusion in the rotifers and Artemia. There was a significant (P < 0.005) prey DHA dose dependent range effect on the abundance of photoreceptor cells in the retina of 34 DPH larvae. The gene expression of rhodopsin in GSB larvae was significantly (P<0.05) upregulated with dietary DHA dose range and larval age (P<0.0001). This study established a link between dietary DHA level with photoreceptor abundance and rhodopsin expression, which led to improved vision, prey acquisition, and growth in developing GSB larvae

The effect of algal turbidity on larval performance and the ontogeny of digestive enzymes in the grey mullet (Mugil cephalus)

A study comprised of two trials determined the effects of water turbidity produced by live microalgae and inert clay particles on the larval rearing of grey mullet (Mugil cephalus). Trial 1 evaluated the effect of microalgae produced water turbidity on grey mullet larval performance and digestive tract (DT) enzyme ontogeny. Two microalgae (Nannochloropsis oculata and Isochrysis galbana) water turbidity levels (0.76 and 1.20 NTU, respectively) and a non-microalgae control (0.26 NTU) were investigated on 2 to 23 dph grey mullet larvae. The higher turbidity (1.2 NTU) larvae (5 dph) consumed markedly (P < .05) more rotifers than other treatment fish, independently of the microalgae type. There was no clear effect of the turbidity treatments on DT enzyme ontogeny. However, in all treatments lipase and alkaline proteases appeared to be modulated by the diet. Alkaline phosphatase activity was ca. 8 times higher and α-amylase activity increased 5.3 times in 79 dph fish compared to 40 dph individuals. The ratio of alkaline phosphatase and leucine-alanine aminopeptidase indicated gut maturation occurred around 61 dph. Trial 2 compared the most effective N.occulata produced turbidity level (1.2 NTU) with the identical water turbidity produced by inert clay on larval performance. M. cephalus larvae exposed to high algal turbidity demonstrated superior performance (P < .05), in terms of rotifer ingestion, dry weight gain and survival, compared to cohorts reared under the clay treatment and the lower microalgae produced turbidity. These findings suggested that water algal turbidity is not the dominant factor determining improved grey mullet larval performance.info:eu-repo/semantics/acceptedVersio

The effect of dissolved carbon dioxide (CO2) on the bone mineral content and on the expression of bone-Gla protein (BGP, Osteocalcin) in the vertebral column of white grouper (Epinephelus aeneus)

The aim of this study was to test the effect of long-term dissolved CO2 exposure on white grouper (Epinephelus aeneus). 45 day post hatching (dph) groupers (0.4 ± 0.05 g; 2.1 ± 0.1 cm) were equally distributed to 15 aquaria (17 L) at a density of 40 larvae per aquarium. The fish were grown for 60 days at a salinity of 25 ppt (26.5 οC) while being exposed to three dissolved CO2 concentrations: Control (0.8 ± 0.1 mg L−1; pH 7.9 ± 0.1), Medium (5.5 ± 0.2 mg L−1; pH 7.1 ± 0.1) and High (28.5 ± 1.5 mg L−1; pH 6.2 ± 0.1). Analysis of bone mineral contents showed that at the end of the CO2 exposure period (105 dph), the Ca levels were significantly higher (P  .05). The gene expression of bone Gla protein (BGP, Osteocalcin), a marker for skeletal mineralization, was significantly higher in the vertebral column of the fish from the control treatment as compared to the medium (P < .05) and high (P < .01) treatments. The expression of BGP mRNA was positively correlated with the fish growth rate, as the fish from the control treatment presented the highest body weight at the end of the experiment