Edible crabs constitute one of the major sources of nutritious food for human nutrition. The study was aimed to examine the protein, amino acid and fatty acid compositions of two edible crabs (Callinectes amnicola and Portunus validus) of Lagos coast, Nigeria. Samples were obtained from the water body, transported in crushed iced insulated containers and analyzed in the laboratory using standard methods. Crude protein varied from 55 - 68.92% (C. amnicola) and 51.9 - 67.51% (P. validus) on dry matter basis. Leucine (8.63 - 9.73g/100 g crude protein) and glutamic acid (12.71 - 16.19g/100 g crude protein) were the highest concentrated essential and non-essential amino acids, respectively. The coefficient of variation of the amino acid values indicated that C. amnicola has more variations, relative to its mean. The most concentrated saturated fatty acid was palmitic acid in the samples with significantly different (P <0.05) values of 14.32±1.05% (C. amnicola) and 24.52±0.00% (P. validus). With the exception of lauric, arachidic and lignoceric, all saturated fatty acids were more concentrated in P. validus than in C. amnicola. Oleic acid among the monounsaturated fatty acids occupied the highest position in C. amnicola (17.6233±0.04%) and in P. validus (12.4682±0.25%); whereas timnodenic acid was the most concentrated among the polyunsaturated fatty acids, with values of 23.9744±0.48 % (C. amnicola) and 15.7234±0.25 % (P. validus). Both species have reasonable levels of dietary protein and lipid quality. J Bangladesh Agril Univ 17(3): 396–401, 2019

Haematological profiles are often applied as an index of physiological condition of various organisms and thus provide information about the health status of local populations. The haematological and biochemical parameters of the estuarine crabs, Callinectes amnicola, Goniopsis pelii, Sersama huzardii and Uca tangerii from the polluted creek of Lagos Lagoon were examined using standard methods. C. amnicola (121.7±0.21) were significantly heavier than G. pelli (24±2.11 g), S. huzardii (16.15±15.19 g) and U. tangeri (8.8±0.5 g). Mean haematological values of the crabs revealed significant variations in total haemocyte count (THC), haemocyte sedimentation rate (HSR) and haemocyte subpopulation. THC in the circulating haemocytes of the crabs was similar for both G. pelli (2150±56.69 mL) and S. huzardii (1975.00±74.46 mL). HSR was lowest in G. pelli (1.50±0.71 mm/hr) and highest in U. tangeri (5.70±0.82 mm/hr). Haemocyte sub-population variables showed that eosinophil and basophil did not differ considerably among the crabs. Significant differences were however recorded for granulocyte, agranulocyte and monocyte with G. pelli having the highest sub-population of granulocyte (33.00±1.41 %) but lowest agranulocyte (67.00±1.41 %). Non-significantly higher sub-population of monocytes was recorded for C. amnicola (3.3±0.03). In the mean values of the serum biochemicals, U. tangeri showed lowest values for all except aspartate aminotransferase (22.8 U/L) and Urea (32.48 mg/dl). G. pelli showed highest values for serum protein (14.36mg/dl), Globulin (67.49 mg/dl) and phosphatase alkaline phosphatase (34.50 U/L). The study gave an indication of stress on the health status of the estuarine crabs, hence the need for periodic monitoring of the ecosystem.

The ecological health status of aquatic environment is a determinant for the survival and growth of organisms within such niche. An investigative study was carried out on four crab species – Cardiosoma armatum, Goniopsis pelli, Callinectes amnicola, Portunus validusinhabiting contaminated sites in Lagos Lagoon- exploring their anti-oxidant defense mechanism in the light of heavy metal concentration in the crab tissues. Amongst the measured heavy metals, cadmium level proved to be significantly highest (P<0.05) with range concentration of 0.42±0.12mg/kg (G. pelli)- 0.79±0.06 mg/kg (C. armatum). Contrastingly, lead was marginally low with concentration below 0.01 mg/kg in all the crab species. Organismal responses to environmental pollution showed a high level of biomarkers. C. armatum was observed to have elevated level of superoxide dismutase (123.04±0.01min/mg/pro), catalase (7.74±0.05min/mg/pro), glutathion transferase (18.21±0.02 Hmol/mg pro), reduced glutathione (2.92±0.04Hmol/mg pro) and glutathione peroxidase (61.85±0.06 Hmol/mg pro) above other species with C. amnicola recording the lowest concentration of the biomarkers. With the low level of heavy metals and corresponding high concentration of these biomarkers, the pollution indices within the study habitat are quite modest.

Bivalve mariculture is a type of molluscan farming done in open seawater on racks, rafts or longlines where naturally occurring phytoplankton serves as a key food item, introduced into the enclosures with the normal circulation of seawater. Increasingly, the reverse trophic interaction is being recognized; dissolved inorganic and organic waste compounds released by metabolically active bivalves can supply phytoplankton with nutrient and energy requirements for their growth. This two-way interaction can be viewed as a type of community symbiosis developed over long evolutionary timescales. The extent to which this affects overall nutrient budgets and thus primary production is related to the system flushing rate and residence time. Here we reviewed the feeding mechanism and nutrient recycling activities of bivalve and also emphasized the role of phytoplankton as a key nutritional live feed in sustainable bivalve mariculture. Bivalves influence nutrient dynamics through direct excretion and indirectly through microbial mediated remineralisation of their organic deposits in the sediments. The quantitative knowledge of bivalve - phytoplankton trophic interactions in coastal waters will inform bivalve mariculture development to effectively serve the needs of both seafood production and ecosystem restoration.

Meat quality in terms of its nutritional value, is a major factor when considering dietary items. This study highlighted the proximate and mineral compositions in the meat of Land Crab, Cardiosoma armatum (Herklots, 1851) fed with Trash Fish (Natural feed) and formulated diet for three (3) months. The meat proximate composition of both crabs fed the two different diets was similar, and there was no significant difference in the crude protein, fat and fiber contents of the meat (p > 0.05). The diets had no significant effects on magnesium, sodium, potassium and phosphorus contents of the meat. Crabs fed formulated diet had significantly higher calcium content of 20428.52±0.10 mg/100 g, compared with the crabs fed with Trash Fish of 18541.83±0.10 mg/100 g (p < 0.05). The pattern of mineral contents in both crabs was calcium > phosphorus > magnesium > sodium > potassium. This study suggested no negative effects of formulated diet on the meat quality. Therefore, formulated diet could be used for fattening of Land Crabs.