Organogenesis of the digestive system in Pacific red snapper (Lutjanus peru) larvae

This study reports the ontogenetic development of the digestive system of larval Pacific red snapper (Lutjanus peru), an important candidate species for aquaculture on the Pacific coast of Mexico. Histological sections of larvae were cut and dyed using the haematoxylin–eosin technique. The development of the digestive tract of Pacific red snapper larvae follows a general pattern of differentiation that can be divided into three stages. Stage I lasted from 1–3 days post hatching (DPH) and included the endogenous nutrition period; it was characterized by the initial differentiation of the digestive tract in preparation for the onset of exogenous feeding (3 DPH). At this time, the digestive tract was differentiated into buccopharynx, oesophagus, stomach anlage, anterior intestine, posterior intestine and a short rectum. The liver, pancreas and kidney were also present. The mouth and anus were open. Stage II occurred after first feeding, lasted for 16 days (4–23 DPH) and included both preflexion and flexion larvae. The main changes that occurred during this stage reflected the adaptation to exogenous feeding and the concomitant growth. Stage III (24–30 DPH) included post‐flexion larvae and started with the appearance of the gastric glands and pyloric caeca. The presence of the gastric glands suggests that early weaning during culture trials of the Pacific red snapper larvae may be possible at this early age.     

Serological evidence of continuing high Usutu virus (Flaviviridae) activity and establishment of herd immunity in wild birds in Austria

Usutu virus (USUV), family Flaviviridae, has been responsible for avian mortality in Austria from 2001 to 2006. The proportion of USUV-positive individuals among the investigated dead birds decreased dramatically after 2004. To test the hypothesis that establishment of herd immunity might be responsible, serological examinations of susceptible wild birds were performed. Blood samples of 442 wild birds of 55 species were collected in 4 consecutive years (2003--2006). In addition, 86 individuals from a birds of prey rehabilitation centre were bled before, at the peak, and after the 2005 USUV transmission season in order to identify titre dynamics and seroconversions. The haemagglutination inhibition test was used for screening and the plaque reduction neutralization test for confirmation. While in the years 2003 and 2004 the proportion of seropositive wild birds was <10%, the percentage of seroreactors raised to >50% in 2005 and 2006. At the birds of prey centre, almost three quarters of the owls and raptors exhibited antibodies before the 2005 transmission season; this percentage dropped to less than half at the peak of USUV transmission and raised again to almost two thirds after the transmission season. These data show a from year to year continuously increasing proportion of seropositive wild birds. The owl and raptor data indicate significant viral exposure in the previous season(s), but also a number of new infections during the current season, despite the presence of antibodies in some of these birds. Herd immunity is a possible explanation for the significant decrease in USUV-associated bird mortalities in Austria during the recent years.     

Induction of triploidy in spotted sand bass (Paralabrax maculatofasciatus Steindachner, 1868) by cold shock

Conditions for the induction of triploidy with cold shock of fertilized eggs of the spotted sand bass Paralabrax maculatofasciatus (Steindachner) were investigated. Different temperatures (12, 8 and 4 °C), timing of cold shock application (5, 10 and 15 min after fertilization) and duration of the shock (5, 10, 15 and 20 min) were tested. Triploidy was determined using flow cytometry at 12 h after larvae hatched. Triploids were produced only when the cold shock treatment was applied 5 min after fertilization. No significant difference was observed in the percentage of triploidy between temperature and the shock duration. At 8 and 4 °C, 100% triploidy was obtained at different durations of cold shock. Survival was significantly lower at 12 or 4 °C than at 8 °C. No significant difference was observed for shock duration at the temperature of 8 or 12 °C; however, at 4 °C, survival was significantly lower at longer durations. We recommend induction of triploidy by applying cold shock at 8 °C for a duration of 15–20 min starting at 5 min after fertilization, in the spotted sand bass.     

Effects of culture conditions on feeding response of larval Pacific red snapper ( Lutjanus peru, Nichols & Murphy) at first feeding

Feeding incidence or number of larvae with preys (FIC) and intensity or number of prey per larvae (FIT) at first feeding of Pacific red snapper ( Lutjanus peru) larvae was investigated under different conditions: prey type (rotifer and copepod nauplius) and density, nauplii size, light intensity, water temperature, salinity and microalgae concentration. Rotifers were not consumed at any prey density and FIC increased significantly when a high nauplii density (10 > 1, 0.1 mL^?1) and light intensity (2000 > 1000, 500, 0 lx) were supplied. In a multifactorial experiment where light intensity (2000, 2500, 3000 lx), tank colour (grey and black) and prey type (nauplii and a mixed diet: rotifers and nauplii) were tested, a significant difference was found only for light intensity and prey type with a significant interaction between these factors. FIC was significantly higher with nauplii stage I–III than IV–VI and also at 25 °C than at 28 °C. Green water (0, 0.3 × 10⁶ or 1 × 10⁶ cells mL^?1) and salinity (25, 30, 35 gL^?1) did not affect FIC. FIT was not affected by any variables tested except in the density experiment where it was significantly higher at 10 nauplii mL^?1.     

The effect of light intensity on first feeding of the spotted sand bass Paralabrax maculatofasciatus (Steindachner) larvae

The effects of light intensity on feeding incidence and prey consumption at first feeding of spotted sand bass larvae (Paralabrax maculatofasciatus Steindachner), using four light intensity treatments (0, 100, 400, and 700 lx) were evaluated. Specimens were fed the rotifer Brachionus plicatilis at a density of 3 rotifers mL^?1. One hour after the addition of prey, 30±3 (mean±SEM) larvae were sampled from each treatment aquarium. Feeding incidence was evaluated as the percentage of larvae with prey in the digestive tract. Feeding intensity was measured as the number of prey in the digestive tract of the larvae. Histological analysis was carried out to describe the eye structure at the time of first feeding. Larvae fed in darkness (0 lx) had a significantly lower (P<0.05) feeding incidence (1.2±2.2%) and intensity (0.4±0.7 rotifers larvae^?1) than those larvae fed at 100 (28±11%, 1.8±0.2 rotifers larvae^?1), 400 (48±10%, 2.4±0.3 rotifers larvae^?1), and 700 lx (52±4%, 2.4±0.1 rotifers larvae^?1). Feeding incidence of the spotted sand bass larvae increased with light intensity while the feeding intensity showed no significant difference (P>0.05) between light treatments. Histological analysis of the eye structure showed that first feeding larvae had well‐formed lens along with a retina composed of pure single cones as photoreceptors.