History and development of shellfish cultivation in Walvis Bay, Namibia.

Namibia is one of the countries in Africa with a favourable natural environment for mariculture operations, particularly shellfish production. The nutrient-rich Benguela upwelling system of the Atlantic Ocean gives the Namibian coast a competitive advantage over other worldwide producers of shellfish, especially, oysters, mussels, abalone, scallops and others. Walvis Bay is Namibia 's biggest harbour town on the western Atlantic coast, where a well established commercial fisheries industry exists along side the country's largest mariculture centre. Other centres of mariculture production include Luderitz, (another fishing town on the southernmost part of the coastline), Swakopmund (30 km from Walvis Bay) and Henties Bay (100 km from Walvis Bay). Shellfish production in Walvis Bay is principally oyster farming and the species produced are the Pacific Oyster (Crassotrea gigas) and the European flat oyster (Ostrea edulis). These have been described as the best oysters in the world due to their exceptional taste and favourable meat-to-shell ratio (Hempel, 2006) and Namibia was ranked amongst the top 20 world leading exporters of oysters (FAO FishSTAT Commodities and Trade, 2006). However, production in 2008 significantly declined due to unexpected harmful algal blooms, the so called red tide phenomenon that resulted in the death of over 75% of all farmed oyster stock. Farmers are currently recuperating from this catastrophe. Besides oysters, mariculture production of other shellfish species in Walvis Bay is negligible but includes the Black mussel (Choromytilus meridionalis), the indigenous clams (Venerupis spp), indigenous scallops (Pecten spp). Cultivation of other shellfish such as abalone (Haliotis midae) and finfish such as Cobia (Rachycentron canadum), dusky kob (Argyrosomus japonicus) and turbot (Psetta maxima) is still being investigated. So far, the mariculture of shellfish in Walvis Bay is believed to have created over 120 jobs, both directly and indirectly.

Flavor Quality Changes of Turbot (Psetta maxima) Stored at -2 and 0°C

The effect of super-chilling at -2°C compared with ice storage at 0°C on flavor quality changes of turbot (Psetta maxima) was investigated. Changes in total volatile basic nitrogen (TVB-N), sensory attributes and volatile compounds were periodically examined for 20 days. Results demonstrated that super-chilling retarded the increases of TVB-N values and maintained better sensory quality compared to the ice storage. Additionally, GC-MS analysis showed super-chilling could more effectively maintain the characteristic volatiles responsible for fresh fish flavor and reduce the contents of putrid compounds such as TMA and acetic acid.

Bioconcentration of Essential and Nonessential Elements in Black Sea Turbot (Psetta Maxima Maeotica Linnaeus, 1758) in Relation to Fish Gender

This study investigates the influence of gender in the bioconcentration of essential and nonessential elements in different parts of Black Sea turbot (Psetta maxima maeotica) body, from an area considered under high anthropogenic pressure (the Constanta City Black Sea Coastal Area in Romania). A number of 13 elements (Ca, Mg, Na, K, Fe, Zn, Mn, Cu, Ni, Cr, As, Pb and Cd) were measured in various sample types: muscle, stomach, stomach content, intestine, intestine content, gonads, liver, spleen, gills and caudal fin. Turbot adults (4–5 years old) were separated, according to their gender, into two groups (20 males, 20 females, respectively), and a high total number of samples (1200 from both groups) were prepared and analyzed, in triplicate, with Flame Atomic Absorption Spectrometry and High-Resolution Continuum Source Atomic Absorption Spectrometry with Graphite Furnace techniques. The results were statistically analyzed in order to emphasize the bioconcentration of the determined elements in different tissues of wild turbot males vs. females, and also to contribute to an upgraded characterization of the Romanian Black Sea Coast, around Constanta City, in terms of heavy metals pollution. The essential elements Mg and Zn have different roles in the gonads of males and females, as they were the only elements with completely different patterns between the analyzed groups of specimens. The concentrations of studied elements in muscle were not similar with the data provided by literature, suggesting that chemistry of the habitat and food plays a major role in the availability of the metals in the body of analyzed fish species. The gender influenced the bioaccumulation process of all analyzed elements in most tissues since turbot male specimens accumulated higher concentration of metals compared to females. The highest bioaccumulation capacity in terms of Ca, Mg, Na, Ni, As, Zn and Cd was registered in caudal fin, liver and intestine tissues. Also, other elements such as K, Fe, Cu and Mn had the highest bioaccumulation in their muscle, spleen, liver and gills tissues. The concentrations of toxic metals in Black Sea turbot from this study were lower in the muscle samples compared with the studies conducted in Turkey, suggesting that the anthropogenic activity in the studied area did not pose a major impact upon the habitat contamination.