No description available.

Although considerable evidence exists to suggest that certain populations of scallops, Pecten maximus (L. ) are reproductively isolated, attempts to date to differentiate populations using data from allozyme electrophoresis have been unsuccessful. In order to further investigate the population structure of this species, genetic differentiation was quantified using mitochondrial DNA (mtDNA) markers and the results compared to morphological comparisons and allozyme variation. A multivariate morphological study revealed little variation in shell shape although animals from Brest and La Trinite (Brittany, France) appeared to have longer hinges. A population from Saint Brieuc Bay, Brittany which exhibits differences in reproductive cycle from neighbouring populations could not be separated on the basis of shell shape although unquantified differences in shell colour were noted. Allele frequencies at 7 loci assessed by allozyme electrophoresis were essentially homogeneous throughout the sample range in accord with previous studies and provided little evidence for population subdivision. Length variation of the mtDNA was extensive, therefore variability was assessed through a PCR approach in order that this did not cause analytical problems. On the basis of sequence divergence data there was convincing evidence that P. maximus from Mulroy Bay, Eire, a semi-enclosed sea lough, were genetically differentiated from all other samples. This could not be unequivocally attributed to a reduction in gene flow since the sample consisted of an ongrown single spatfall. Although no distinct pattern of mtDNA haplotype frequencies was apparent, the frequency of the commonest haplotype varied between sites with a pattern similar to that of allozyme allele frequencies in Aequipecten opercularis, a scallop species with a similar distribution and life history for which there is evidence of considerable population subdivision. In comparisons of P. maximus and the closely related P. jacobaeus no consistent differences were detected in morphology, allozymes or mtDNA data. The taxonomic standing of P. jacobaeus is brought into question.

It is confirmed that Mac brachium match r ii contains much lower w3 HUFA levels than marine prawns. For larvae which have a low HUFA profile at stage I. survival and growth vary in relation to dietary linolenic acid which is the precursor of these long chain fatty acids. Diets containing different levels of w6 fatty acids produced large differences in survival and slight differences in growth. Recently hatched larvae utilize saturated and monounsaturated fatty acids for their energy requirements, as PUFA's increase from stage I to stage II, suggesting that larvae are able to chain elongate. Heavier M. n2ank ii females have heavier clutches and higher numbers of eggs. However, female weight does not influence weight per egg, nor the volume of each egg. The length of incubation does not significantly influence the larval survival though a negative trend is observed. The ratio between the weight of the parent female and the weight per egg (Wegg/W) is found to be 0.036 which reflects a poor fecundity. Recently hatched larvae consume microencapsulated feed, but do not survive beyond day 13. However, artificial diets can be fed successfully from stages VI-VII, the best growth occurring at a feeding rate of 8-16mg of microcapsules per litre. For the caridean M. ma br; zi and penaeid a=LtUa m2nQdgn larvae, edge index increases from 641 and 223, respectively, at the beginning of their development to 1847 and 750 at the end, reaching 2817 and 5000 at postlarval metamorphosis. These results confirm the herbivorous, omnivorous and raptorial feeder classification given by Itoh (1970). Recently hatched M. rosenbargii larvae show poor ability to crush their food and rely heavily on their embryonic lipid droplet reserves. Later, they feed on live diets, such as Artamin and rotifers, containing their own enzymes which aid larval digestion. Between stages V and VII, the cardiac foregut becomes muscular, the pyloric filter apparatus is functional, and the hepatopancreas increases rapidly in size. Residence time of food becomes longer in the foregut, but remains the same, and later decreases, in the midget. Survival and growth on artificial feed coincide with these changes, suggesting that larval enzyme production is sufficient to digest and assimilate such diets.

The effects of live foods and microencapsulated diets on growth, survival, body composition and digestive physiology of fish (mirror carp, Cyprinus =LQ) and penaeid shrimp ftna= japQnim) larvae were examined. Raising the lipid content of a microencapsulated enrichment diet from 18.3% to 33.6% improved accumulation of highly unsaturated fatty acids (HUFA) and total lipid in rotifers. Lipids in rotifers were assimilated by carp larvae, as demonstrated by improved growth and accumulation of HUFA in larvae reared on rotifers pre-fed the "high-lipid" diet. Poor diet digestibility coupled with low ingestion rates and low digestive enzyme activity in larvae were identified as contributing to the failure of a microencapsulated diet to support good growth and survival when fed directly to first-feeding carp. Preliminary testing indicates that digestibility of microencapsulated diets for fish larvae can be improved by inclusion of pancreatin. Experiments with Penaeus japonicus indicate that dietary requirements for protein, energy and HUFA by penaeid larvae are lower than previously thought. Foods of low protein content (Chaetoceros gladlia) or low digestibility (microencapsulated diet) elicited high trypsin activity in mysis larvae, compared to those fed Artemia. Larvae receiving both C , gmcilis and Artemi exhibited an intermediate level of trypsin activity - which may explain the superior growth and protein retention in postlarvae reared on the mixed regime. A microencapsulated diet did not support growth and carbon and nitrogen retention equivalent to that in larvae fed live food, despite the strong trypsin response, in mysis larvae. When used together with a low density of _C, p-racilis the microencapsulated diet produced postlarvae of the same size and tissue composition as those reared using live food. It is suggested that the algal co-feed may enhance growth through stimulation of trypsin secretion, supply of extra digestible nutrients or provision of unidentified specific growth enhancing factor(s).

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.

No description available.

No description available.

No description available.

No description available.