Environmental conditions in form of light intensity, phosphorus and nitrogen limitation were used to manipulate the biochemical composition of continuous cultures of Skeletonema costatum, Chaetoceros muelleri, Rhinomonas reticulata and Pavlova lutheri. Crude protein, carbohydrate and chlorophyll content as well as the fatty acid profile was determined in the combinations of two light intensities (high and low light, HL and LL) and three nutrient conditions (no nutrient limitation, f/2, phosphorus limitation, P, and nitrogen limitation, N). They were fed to Mytilus edulis larvae over a two week period and the larval size and mortality were assessed; the larval fatty acid profile of various batches of eggs as well as after the end of the feeding trial was also determined. A novel computer aided image analysis technique was used for measuring the length ofthe larvae. All monospecific diets supported good growth, sometimes equal or better to a control diet which was a mixture of species (R. reticulata and P. lutheri). In general survival was not affected by the diets and was found to be related more with the specific batch of larvae used. On the contrary growth was correlated with the diet. Ranking of the S. costatum diets was: LL N =LL f/2 =LL P =HL N >Control >HL f/2 =HL P. The C. muelleri diets were ranked as: LL N =LL f/2 >Control >HL f/2 =HL P =HL N >LL P. The R. reticulata diets are ranked, again in decreasing quality order as: HL N =LL f/2 =Control >LL N >HL f/2 =HL P =LL P. The P. lutheri ranking order was: HL N =HL f/2 =HL P =LL P >LL N =LL f/2 >Control. The larvae were analyzed for their fatty acid profile and relative content and some fatty acids were significantly correlated with growth thus enabling the usage of certain fatty acids as an index of growth for M. edulis larvae. Larval 20:5(0:3 and Polyunsaturated fatty acids (PUFA) were a positive index of growth while 15:0 and Saturated Fatty acids (SaFA) were a negative index. A multidimensional model was used in an effort to correlate algal biochemical components with larval growth. Some fatty acids were found to be the main factors in determining the algal biochemical composition with protein and carbohydrate playing a secondary "modifying" role. In the case of P. lutheri the 16:0 and SaFA were positively correlated with larval growth in an almost linear fashion while omega: 3 fatty acids were negatively correlated with larval growth. A positive correlation concerning the 16:0 and a negative one for the PUFA was also established in S. costatum and R. rcticulata.

Shrimp are the most valuable fish stock in Bahrain waters, the fishery being based on a single species P. semisulcatus which forms about 95 percent of the total landings. In 1993, shrimp landings formed 23.8 percent of the total Bahrain fish landing, which totalled 2,128 tonnes at a first sale value of 5.4 million Bahraini Dinars (1 DS$.0.380 BD). Beside the increased fishing effort, the marine habitat of Bahrain suffers from several sources of pollution. Most evident is dredging and reclamation which have altered most of the coastal areas. Despite the shrimp fishery importance and the development-related stresses on Bahrain coastal environments, there were limited basic data on this valuable stock. The current study aimed to provide as full an understanding as possible of the shrimp fishery of Bahrain. Several surveys were conducted on the shrimp populations and their environment. A sediment survey was conducted from 9 August to 26 October. From May 1991 to May 1992, a regular sampling programme was initiated to record the physical properties of the sea water at fixed stations in TUbli Bay and off Mina Sulman. Physical properties of sea water were also recorded in the open sea during June 1980, October and December 1991. Plankton collection was conducted mainly through two sampling programmes. The first was conducted in the open sea from September 1991 to January 1992 (excluding November 1991). The second programme was restricted to Tubli Bay; samples were obtained over periods from May 1991 to June 1992 inclusive and from March to May 1993. Two major benthic surveys were completed. The first was conducted from June 1980 to June 1981 using an industrial trawler, covering the whole shrimping ground, except TUbli Bay. A second survey was carried out on the shrimp population in TUbli Bay from May 1991 to June 1993 in three time periods, from May 1991 to June 1992, November 1992 and from April to June 1993. Based on the above surveys, physical properties of sea water and bottom sediment of the shrimping ground were described. Also the bionomics of the seven penaeid species found in Bahrain waters were determined. Benthic and plankton surveys revealed spawning activities of P. semisulcatus restricted to the offshore waters. Also prolonged spawning activity was determined for this species, which most significantly occurred from August to March. P. semisulcatus main recruits appeared in the shrimping grounds from April to July, originating from nurseries found within the areas A and B. Two migration patterns were determined for P. semisulcatus within Bahrain shrimping grounds throughout a season. The updated information on shrimp fishery generated by the current work provides a basis for identification of areas for further improvement of this fishery. Consequently, the work determines of future investigations necessary for Bahrain shrimp fishery.

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