The big advantage of using molecular biomarkers to monitor oxygen levels in aquatic systems is that responses at the molecular level tend to be more sensitive, and usually occur earlier than those at higher levels of biological organization Aquatic hypoxia is a frequent event, which can occur naturally in a variety of marine, estuarine and freshwater habitats. More often, however, hypoxia arises as a result of euthrophication of aquatic ecosystem and can lead to changes in community structure by eliminating hypoxia-sensitive species. Consequently fish have develop various physiological and biochemical mechanisms to cope with this environmental stress. Many of these adjustments depend to changes in expression of a wide range of genes. The transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factor-1 (HIF-1), a heterodimer composed of an α and β subunit. This study investigated if HIF-1α mRNA levels were regulated by hypoxia in Eurasian perch (Perca fluviatilis), a hypoxia-sensitive fresh water species. The real-time PCR was utilized to monitor dynamic changes in levels of HIF-1α mRNA in response to acute (DO 0.4 ± 0.1 mg/l for 1 h) and chronic (DO 2.8 ± 0.3 mg/l for 15 days) hypoxia. Our results indicated an up-regulation of HIF-1α in brain and liver, but not in muscle tissue after acute hypoxic treatment, whereas significant changes of HIF-1α mRNA levels were detected in muscle, but not in brain and liver after chronic hypoxia exposure. This study suggests that HIF-1α mRNA level in selected perch tissues could be an useful indicator of acute exposure to hypoxia.

No data have previously been reported on Eurasian perch Perca fluviatilis L. in Lake Varese. In this study, the growth, diet, and reproductive biology of the Eurasian perch population were investigated with the aim of providing information that may serve as a basis for efficient resource management. A total of 240 specimens were caught during the monthly sampling campaign from November 2006 through October 2008. The length-to-weight relationships were W t = 8.4 × 10−3 L t 3.10 (males) and W t = 4.1 × 10−3 L t 3.36 (females). The parameters for the von Bertalanffy growth function for pooled sexes were L ∞  = 33.17 cm, k = 0.20 year−1, and t 0 = −1.34 year. Perch in Lake Varese spawn from April through May. Sexual maturity is reached when males are 2 years old, in females mostly when they are 3 years old. Relative fecundity (F rel) and absolute fecundity (F abs) were assessed for females. Fecundity values were similar to data reported for other European populations: females of age 2+ F rel = 102,457 ± 12,275, age 3+ F rel = 131,767 ± 5,891, and age 4+ F rel = 131,252 ± 15,555. Perch diet spectrum was wide and somewhat characterized by season. Perch in Lake Varese feed on macroinvertebrates, mainly Chironomidae and Chaoborus, zooplankton, and juvenile rudd Scardinius erythrophthalmus.

Eurasian perch (P. fluviatilis) is a very important fish species in Varese lake (N-W Italy). Since the second half of 20(th) century, perch catches in the lake have steadily decreased and by the end of the '80s the species resulted clearly endangered. The purpose of this study was to investigate growth, mortality and feeding conditions of perch post-larvae, reared in illuminated floating cage in Varese lake, to obtain fingerlings for a restocking program. In June 2006 and 2007, groups of 280 and 300 pre-weaned post-larvae (average body weight 0.64 +/- 0.09 g and 0.25 +/- 0.08 g respectively P<0.01) were held in an illuminated net cage for 90 days. The cage was illuminated inside from 20:30 p. m. to 6:30 a. m. During the trial, the nightly zooplankton accumulation inside the cage was assessed weekly. At night time the zooplankton biomass, which resulted dominated by Cladocera family, was higher inside the cage than in the lake. In 2006, 322 +/- 36 zooplankters L(-1) were observed, compared to 945 +/- 600 observed in 2007 (P<0.05). In the lake, the number of zooplankters per litre was similar in both years, resulting in 63.3 +/- 50.30 and 61.10 +/- 45 zooplankters L(-1), respectively on 2006 and 2007. In order to assess perch growth performances, 25 fishes were sampled from the cage every 15-20 days and length (cm) and weight (g) were assessed for each sample. At the end of September, specific growth rate (SGR) and survival rate were assessed. In 2006 the final mean body weight of the perch fry was 4.65 +/- 1.47 g and that results significantly lower (P<0.05) than of 2007 (6.3 +/- 1.69 g). The SGR was 2.04% and 3.42%, respectively. The higher growth rate observed in 2007 was influenced by a higher zooplankton accumulation in the cage due to an improved cage management. In order to assess the cage efficiency, in September 2006 and 2007, the weight of young-of-year perch (n=50) captured in the lake were compared to those of reared fish. Wild fry showed a mean body weight significantly higher (P<0.05) than reared ones (15.90 +/- 4.25 g and 17.86 +/- 4.47 g in 2006 and 2007, respectively). The survival percentages resulted 50.7% in 2006 and 60.7% in 2007. The results demonstrate that the rearing of perch in illuminated floating cages enables the possibility to produce fry for restocking programs in Varese lake.

Aquatic hypoxia is a frequent event and in fish a complex set of physiological and biochemical alterations are employed to cope with this environmental stress. Many of these adjustments depend to a large extent on changes in the expression of genes that encode for physiologically relevant proteins. Genes that are induced by hypoxia appear to share a common mode of transcriptional regulation. This induction depends upon activation of a transcription factor, the hypoxia inducible factor-1 (HIF-1), which is a heterodimer composed of two subunits: alpha and beta.In this study we report first on the molecular cloning and characterization of HIF-1 alpha in sea bass (Dicentrarchus labrax). The full-length sea bass cDNA for HIF-1 alpha was isolated and deposited in the GenBank with accession no. DQ171936. It consists of 3317 base pairs (bp) carrying a single open-reading frame that encompasses 2265 bp of the coding region and 1052 bp of the 3' UTR.We then utilized the real-time PCR technology to monitor dynamic changes in levels of HIF-1 alpha transcripts, in response to acute and chronic hypoxic stress. The number of HIF-1 alpha mRNA copies were significantly increased in response to both acute (1.9 mg/L, dissolved oxygen for 4 hours) and chronic (4.3 mg/L, DO for 15 days) hypoxia in sea bass, whereas it remained unchanged in fish exposed to hyperoxic (DO 13.5 +/- 1.2 mg/L, 155 % saturation) conditions. This is the first study carried out to investigate the behaviour of HIF-1 alpha gene transcripts during hypoxia in representative of marine hypoxia-sensitive fish species.

In recirculating aquaculture systems (RAS), particulate matter and bacterial communities management are required to maintain water quality. Foam fractionation is a water treatment technology that can be easily applied to water reuse systems to remove bacteria and suspended solids. This study investigated the efficiency of foam fractionation in removing particulate matter and heterotrophic bacteria in a closed recirculating seabass (Dicentrarchus. labrax) system. This system consisted of 10 rearing tanks, a skimmer acting as the foam separation system (SKIM®), a biofilter unit, and an UV unit. The efficiency of SKIM was analyzed for different foam fractionation operation times (5′on/5′off, 15′on/15′off and 30′on/30′off) and for different sizes of particulate matter (>60μm, 60–8μm, 8–1.2μm, and 1.2–0.22μm). The removal of particulate matter was influenced by different particle sizes with higher removal percentages for the >60μm and 1.2–0.22μm categories of 96.8 and 100%, respectively. Nevertheless, these categories represented the lower percentage of total solid compositions in the RAS water studied (>60μm=7.14±2.78%, and 1.2–0.22μm=18.27±2.50%). The removal of heterotrophic bacteria did not correlate with the operation time or particle size and SKIM removal percentages ranged between 32 and 88%.