Sperm quality in relation to age and weight of white shrimp Litopenaeus vannamei

Optimal sperm quality is an important feature for management of shrimp broodstock. The understanding of the sperm quality in relation to age and weight of shrimp is useful to select male broodstock. To evaluate the effect of age and weight on sperm quality, Litopenaeus vannamei males from the same cohort at ages of 6, 8, 10, and 12 months were examined, using body weight as a covariable in ANCOVA. Additionally, males of the same cohort at an age of 12 months, but from different culture conditions, were compared. Spermatophore weight, sperm count, and percentage of normal sperm were positively correlated to body weight. Sperm count was positively correlated to spermatophore weight and percentage of normal sperm. Males at an age of 12 months had superior sperm quality than younger males, based on observations of larger spermatophore weight, higher sperm count, and higher percentage of normal sperm. By eliminating the influence of body weight with the use of ANCOVA, the same effect was still observed, indicating that the effect of age of males on sperm quality was independent of body weight. However, when large differences in growth were forced by changing culture conditions, sperm quality differences were observed and could be explained by body weight. In conclusion, using 12-month-old males would lead to improved shrimp seed production, since they are mature males with high sperm quality. In addition, for improved productivity, it is important to consider the culture conditions under which domesticated male broodstock will be obtained. (C) 2003 Elsevier Science B.V. All rights reserved

The influence of dietary arachidonic acid on the immune response and performance of Pacific whiteleg shrimp, Litopenaeus vannamei, at high stocking density

Stocking shrimp at high densities increases yield during culture, but growth is generally compromised and weakened immune response associated with poor water quality has also been reported. Therefore, we tested if supplying more arachidonic acid (ARA) in the diet, a precursor of eicosanoids such as prostaglandins E from the series II (PGE2) that enhance immune response can counteract the negative effect of stocking shrimp at high densities. The effect of physical crowding was separated from the effect of water quality, both a result of high density, by using tanks divided by a hard plastic net that allowed water flow between two density conditions. Crowding reduced weight gain by 8.3%, although the effect was more evident with deteriorated water quality from combined effects of high total ammonia and low dissolved oxygen levels (18.4%), but no effect on survival was found. A clear food imprinting of ARA levels in hemocytes was observed, but ARA did not clearly counteract the negative effects of high density on overall performance. However, ARA could minimize stress response of sampling and enhance some effectors of the immune system, such as clotting and respiratory burst. The increase in PGE2 metabolite in shrimp fed with the high-ARA diet was not consistent, and thus, the effects of ARA were not necessarily mediated by these eicosanoids

Seasonal variations in larval biomass and biochemical composition of brown shrimp, Crangon crangon (Decapoda, Caridea), at hatching

The “brown shrimp”, Crangon crangon (Linnaeus 1758), is a benthic key species in the North Sea ecosystem, supporting an intense commercial fishery. Its reproductive pattern is characterized by a continuous spawning season from mid-winter to early autumn. During this extended period, C. crangon shows significant seasonal variations in egg size and embryonic biomass, which may influence larval quality at hatching. In the present study, we quantified seasonal changes in dry weight (W) and chemical composition (CHN, protein and lipid) of newly hatched larvae of C. crangon. Our data revealed significant variations, with maximum biomass values at the beginning of the hatching season (February–March), a decrease throughout spring (April–May) and a minimum in summer (June–September). While all absolute values of biomass and biochemical constituents per larva showed highly significant differences between months (P < 0.001), CHN, protein and lipid concentrations (expressed as percentage values of dry weight) showed only marginally significant differences (P < 0.05). According to generalized additive models (GAM), key variables of embryonic development exerted significant effects on larval condition at hatching: The larval carbon content (C) was positively correlated with embryonic carbon content shortly after egg-laying (r 2 = 0.60; P < 0.001) and negatively with the average incubation temperature during the period of embryonic development (r 2 = 0.35; P < 0.001). Additionally, water temperature (r 2 = 0.57; P < 0.001) and food availability (phytoplankton C; r 2 = 0.39; P < 0.001) at the time of hatching were negatively correlated with larval C content at hatching. In conclusion, “winter larvae” hatching from larger “winter eggs” showed higher initial values of biomass compared to “summer larvae” originating from smaller “summer eggs”. This indicates carry-over effects persisting from the embryonic to the larval phase. Since “winter larvae” are more likely exposed to poor nutritional conditions, intraspecific variability in larval biomass at hatching is interpreted as part of an adaptive reproductive strategy compensating for strong seasonality in plankton production and transitory periods of larval food limitation