Effect of season and artificial diet on amino acids and nucleic acids in gonads of green sea urchin Strongylocentrotus droebachiensis

Effects of Supplementary Kelp Feeding on the Growth, Gonad Yield, and Nutritional and Organoleptic Quality of Subadult Sea Urchin (Strongylocentrotus intermedius) with Soya Lecithin Intake History

A 23-week feeding experiment was conducted to investigate the effects of supplementary kelp feeding on the growth, gonad development, and nutritional and sensory properties of sea urchin (Strongylocentrotus intermedius) with soya lecithin (SL) intake history. The feeding experiment was divided into experimental phase I and phase II. During phase I, 48 subadult sea urchins (initial weight: 6.28 ± 0.07 g) were fed one of the feeds with different levels of SL (0%, 1.6%, 3.2%) or kelp (Saccharina japonica) for 12 weeks. Then, all sea urchins were fed kelp for the next 11 weeks during the phase II. Each diet was randomly allocated to six cages of sea urchins. The results of phase I showed that weight gain rate (WGR), gonadosomatic index (GSI), gonad sensory properties (color and texture), and essential amino acid (EAA) contents were not significantly affected by SL level in the feed groups. High level (3.2%) of SL suppressed gonad development of S. intermedius with retarded gametogenesis in the 3.2% SL group (stage Ⅱ) compared to those fed 0% and 1.6% SL groups (stage Ⅲ). Sea urchins fed dry feeds exhibited significantly lower WGR and values of color (redness and yellowness) and texture (hardness and gumminess) but higher contents of EAA in the gonads than those fed kelp. The n-3/n-6 polyunsaturated fatty acid (PUFA) and eicosapentaenoic acid (EPA) of gonads in the groups fed with dry feeds showed no significant differences, but were significantly lower than that of kelp group. At the end of phase II, the gonad yellowness and EPA content of gonads in all dry feed groups were significantly increased by supplementary kelp feeding, with a higher increase observed in S. intermedius with SL intake history, while arachidonic acid (ARA) content was significantly improved by supplementary kelp feeding in S. intermedius with SL intake history. Gonad texture was improved to some extent by supplementary kelp feeding. These results indicated that S. intermedius fed dry feeds showed significantly higher GSI and EAA but poorer organoleptic quality and lower n-3/n-6 PUFA and EPA than those fed kelp. Kelp supplementary feeding improved the fatty acid value and organoleptic quality of gonads, especially for the sea urchins with SL intake history.

Slight Increases in Salinity Improve Muscle Quality of Grass Carp (Ctenopharyngodon idellus)

Fish muscle quality is an important parameter in the aquaculture industry. In this study, we analyzed and compared the muscle quality of grass carp (Ctenopharyngodon idellus) cultured at salinities of 0‰, 3‰, and 6‰ (GC0, GC3, GC6). There was no significant difference in crude protein and crude fat content of muscle between GC0 and GC3. Crude fat was significantly lower in GC6 compared to the other groups. GC3 and GC6 had higher hydroxyproline content, which suggested that these groups had higher collagen content. GC3 and GC6 had higher contents of free amino acids and umami amino acids than GC0, but there was no significant difference in sweet or sour amino-acid content among groups. GC3 and GC6 had better texture properties, including hardness, gumminess, chewiness, resilience, and springiness, than GC0. GC3 had the highest water-holding capacity among the groups. As the salinity increased, the diameter of muscle fibers decreased and the sarcolemma showed a thickening trend. These results suggest that a slight increase in salinity (i.e., 3‰) can effectively improve the muscle quality of grass carp.

Acid-base balance and metabolic response of the sea urchin Paracentrotus lividus to different seawater pH and temperatures

PURPOSE

In order to better understand if the metabolic responses of echinoids could be related to their acid-base status in an ocean acidification context, we studied the response of an intertidal sea urchin species, Paracentrotus lividus, submitted to low pH at two different temperatures.

METHODS

Individuals were submitted to control (8.0) and low pH (7.7 and 7.4) at 10°C and 16°C (19 days). The relation between the coelomic fluid acid-base status, the RNA/DNA ratio of gonads and the individual oxygen uptake were studied.

RESULTS

The coelomic fluid pH decreased with the aquarium seawater, independently of temperature, but this explained only 13% of the pH variation. The coelomic fluid showed though a partial buffer capacity that was not related to skeleton dissolution ([Mg(2+)] and [Ca(2+)] did not differ between pH treatments). There was an interaction between temperature and pH on the oxygen uptake (V (O2)) which was increased at pH 7.7 and 7.4 at 10°C in comparison with controls, but not at 16°C, indicating an upregulation of the metabolism at low temperature and pH. However, gonad RNA/DNA ratios did not differ according to pH and temperature treatments, indicating that even if maintenance of physiological activities has an elevated metabolic cost when individuals are exposed to stress, they are not directly affected during short-term exposure. Long-term studies are needed in order to verify if gonad production/growth will be affected by low pH seawaters exposure.

Broodstock diet effect on sea urchin Paracentrotus lividus (Lamarck, 1816) endotrophic larvae development: potential for their year-round use in environmental toxicology assessment

The effect of captive broodstock diet on fertilization and endotrophic larvae development of the sea urchin Paracentrotus lividus was assessed. Maize grain and five inert pelleted diets were tested, during a three-month experimental period. Maize flour, wheat flour, soybean flour, maize/wheat flour (MWF) and maize/soybean flour mixes were used as vegetal sources for inert feed. Gonad index, percent egg fertilization and larvae malformation occurrence were compared with the results obtained from wild sea urchins (W). Whole egg total amino acid composition was concomitantly analyzed as a tool to explain eventual endotrophic larvae malformations caused by lack of specific nutrients. For all treatment groups (wild and captive), percent egg fertilization values above 96% were always observed, fulfilling the requisites (70-90%) necessary to conduct environmental monitoring bioassays, according to USEPA (2002). Similar values for normal percent larval development were only obtained from P. lividus broodstock subjected to an inert feeding diet based on a maize/wheat flour mix (85.0±1.45%), in comparison to wild P. lividus (82.5±1.75%). Likewise, no statistical differences on resultant whole egg total amino acid composition were observed between P. lividus fed MWF and wild treatments. Moreover, statistical differences between MWF and all the other captive feeding treatments were found for six out of the seventeen amino acids analyzed. This study demonstrates the possibility to obtain high values for P. lividus endotrophic larvae percent normal development based on broodstock held in captivity as long as an appropriate inert diet is provided.