In vitro protein digestibility of different grow‐out stages of spotted rose snapper (Lutjanus guttatus,Steindachner, 1869)

The aim of this study was to compare in vitro protein digestibility between two groups of fish, at early (21 g) and late stages (400 g) of spotted rose snapper Lutjanus guttatus, to evaluate the degree of hydrolysis (DH) and total amino acid release (TAAR) using crude extracts from stomach, pyloric caeca and intestine of 13 protein ingredients including marine, animal and plant meals. Degree of hydrolysis and TAAR were measured by a pH‐Stat method, and the PAGE‐Zymogram was also used as complementary technique. Differences in DH were found between both grow‐out stages mainly in the alkaline hydrolysis phase. Fish and squid meals (marine sources) had the highest DH and TAAR, followed by porcine meat and poultry meal by‐products from recycling sources, and soybean and canola meals (plant sources), which represent better protein sources for use in practical diets. Stomach zymograms showed two pepsin isoforms in both grow‐out stages. Pyloric caeca and intestine zymograms showed five bands with proteolytic activity in the early grow‐out stage, whereas four additional bands were found in late grow‐out stage. Alkaline proteases were identified as serine and metalloproteases. Thus, L. guttatus presents an ontogenetically differentiated digestive enzyme pattern that modifies the DH and TAAR of different protein sources.     

Nutritional stimuli of gilthead seabream (Sparus aurata) larvae by dietary fatty acids: effects on larval performance,gene expression and neurogenesis

The concept of nutritional programming raises the interesting possibility of directing specific metabolic pathways or functions in juvenile fish, for example, to improve the use of substitutes to fishmeal and oil, and hence to promote sustainability in aquaculture. The aim of the study was to determine effects of early nutritional stimuli of gilthead seabream larvae and check if nutritional programming of gilthead sea bream is possible between 16 days post hatching (dph) and 26 dph. A trial was conducted to determine the effects of early nutritional stimuli of gilthead seabream larvae. Five experimental microdiets (pellet size <250 μm) were formulated containing five different proportions of a marine lipid source rich in long‐chain polyunsaturated fatty acids (LC‐PUFA) and two vegetable lipid sources rich in linolenic and linoleic acids. The results of this study demonstrate that dietary n‐3 LC‐PUFA levels increased larval growth and survival affecting Δ6 desaturase gen (fads2) expression and retinal neurons density. However, the high mortalities obtained along on‐growing in fish fed low n‐3 LC‐PUFA at 16 dph constrained the feasibility of nutritional programming of gilthead seabream during this late developmental window and needs to be further investigated.     

Effect of EPA/DHA ratios on the growth and survival of Galaxias maculatus (Jenyns, 1842) larvae reared under different salinity regimes

Despite the importance of certain highly unsaturated fatty acids in osmotic regulation, few studies have been addressed to determine the essential fatty acid requirements for a given species cultured under different salinities. As Galaxias maculatus is a diadromic species, the present study aimed to determine the effect of salinity on the optimum dietary EPA/docosahexaenoic (DHA) ratio for survival and growth during the larval stages. Larvae were fed for 20 days with rotifers containing two different EPA/DHA ratios (low: 0.64 and high: 2.18) at three different salinities (0, 10 and 15 g L^?1). The results of this study showed a marked effect of water salinity on larval dietary lipid utilization in G. maculatus larvae. These results suggested that G. maculatus larvae reared at higher salinities may have a higher dietary requirement for DHA, whereas larvae reared at 0‰ showed higher requirements for EPA. The overall results of the present study indicate that even small changes in salinity can determine the optimum dietary EPA/DHA ratio and the quantitative essential fatty requirements of fish. This may have important repercussions and affect the rearing performance of G. maculatus cultured under different salinities.     

Dietary Lipid Requirements for Optimal Egg Quality of Redclaw Crayfish,Cherax quadricarinatus

The effect of three crude dietary lipid levels (4, 8, and 12%) on egg quality of the female redclaw crayfish, Cherax quadricarinatus, was evaluated. Three replicate groups of 40 crayfish (mean initial weight ± SD, 23.0 ± 3.0 g) per diet treatment were stocked in 15,000 ‐L tanks, at 28 C. After 75 d of culture, there were significant differences (P < 0.001) in egg area (3.52–3.90 mm²), volume (34.0–39.3 mm³), weight (4.81–5.36 mg), and diameter (2.15–2.27 mm) in response to dietary lipids in the diet. Using the quadratic equation, the maximum responses of these parameters corresponded to lipid levels from 8.60–8.84%. There were no significant differences (P > 0.05) in survival (82.1–86.9%), final weight (41.0–43.7 g), number of spawning females (18.12–27.38%), and fecundity (9.07–10.31 eggs/g female). Additionally, there were no significant differences (P > 0.05) in egg mean protein (2306.87 ± 440.08 μg/egg), lipid (441.95 ± 83.23 μg/egg) and carbohydrate (74.81 ± 10.12 μg/egg) contents, and energy (13.49 ± 2.25 kcal/egg). The optimum overall response was obtained for dietary lipid content of 8.7%, which we recommend to optimize egg quality of this freshwater crayfish.