No abstract

The spotted sand bass Paralabrax maculatofasciatus is a species that has been cultured in our laboratory over the past decade (Civera et al. 2002). At ¢rst feeding (day 2 at 25 1C), functional eyes and digestive tract are present (Pen ì a et al. 2003(Pen ì a et al. , 2004, which allows the larvae to begin feeding.First feeding of teleost larvae is considered an important aspect of larviculture. It has been shown that culture conditions including light intensity (Downing & Litvak 1999a), prey density (Werner & Blaxter 1981) and colour of the rearing tank (Downing & Lit-vak1999b) a¡ect feeding e⁄ciency and consequently, larval growth and survival under culture conditions.In a previous study, Pen ì a and colleagues (2004) showed that spotted sand bass larvae are visual predators and that higher light intensity increased feeding incidence and intensity at ¢rst feeding. Culture conditions that enhance feeding e⁄ciency at ¢rst feeding contribute to increased survival rates and reduced risk of starvation during the ¢rst days of development. The present study evaluated the e¡ect of prey density and rearing tank colour on feeding e⁄ciency of spotted sand bass larvae at ¢rst feeding.A spontaneous spawn of spotted sand bass, P. maculatofasciatus, broodstock was maintained in a100 L tank at 25 1C and a salinity of 35% until one day after hatching. The yolk-sac larvae were collected, separated into groups of 500 and transferred to twentyseven 10 L aquaria ¢lled with static, ¢ltered and UV-treated seawater at 25 1C and 35% (density of 50 yolk-sac larvae L À 1 ). Light intensity was 700 lx at the water surface, provided by eight190 cm 70 W full spectrum £uorescent white lamps (Philips, Somerset, NJ, USA) (Pen ì a et al. 2004). At ¢rst feeding (day 2), the larvae were fed rotifers Brachionus plicatilis. Green water, Nannochloropsis oculata, was also added at a density of 300 000 cells mL À 1 . Three tank colours (white, grey and black) in combination with three levels of prey densities (5,10 and15 rotifers mL À 1 ) were tested in triplicate. To provide homogeneous background colour, the aquaria were painted with an epoxy non-toxic paint (Fulmex E-26-B, Prometal, Mexico City, Mexico).The spotted sand bass larvae initiate feeding activity within the ¢rst 3 min after rotifers addition to the rearing tanks (unpubl. results). One hour after feeding, 30 AE 2 (mean AE standard deviation (SD)) larvae were randomly sampled from each aquarium. Sampled larvae were evaluated for feeding e⁄ciency as the feeding incidence (percentage of sampled larvae with prey in the digestive tract) and the feeding intensity (number of prey in the digestive tract). Both measurements were made under a dissection microscope (Olympus SZ40,Tokyo, Japan). A two-way ANO-VA was performed with tank colour and prey density as factors. When signi¢cant di¡erences (Po0.05) were detected, a Tukey's test was applied. Results are reported as mean AE SD.Results showed that feeding incidence was not signi¢cantly a¡ected (P40.05) by the tank colour.

Neobenedenia melleni is a monogenean parasite that causes significant mortality and economic losses in fish aquaculture. Changes in the antigenic composition of this parasite occur during its developmental stages. In this study, we evaluated humoral parameters in serum and transcriptional immune responses of yellowtail naturally infected with N. melleni. In addition, in vitro assays were performed to study the stimulatory effects of antigens from larvae and adults on spleen leucocytes from non-infected fish at 6 and 24 h post-stimulation. The results showed enhanced total protein, myeloperoxidase and antiprotease activities in N. melleni-infected fish compared with non-infected ones. The induction of Toll-like receptors (TLRs) and pro-inflammatory cytokines in spleen leucocytes during natural infection with N. melleni suggests that these immune-related genes play an important role in the initiation of the immune defence mechanism for controlling parasite infection. Interestingly, the magnitude of in vitro responses of spleen leucocytes was dependent on the parasitic stage. An important stimulation of gene expression by adult antigens on spleen leucocytes was observed. Differential expression patterns of TLRs and target cytokines in yellowtail leucocytes in both in vivo and in vitro studies suggest that the quality of yellowtail immune response is conditioned by N. melleni development.