Seasonal variation in the chemical composition of pomfrets. Pt. 1. Black pomfret (Parastromateus niger)

Seasonal variations in proximate composition of the different parts such as head, middle, tail and skin of black pomfret (Parastromateus niger) are reported over three years on monthly basis. The lean and fatty conditions of fish are discussed on the basis of spawning period, food and feeding activity, size group appearance and the gonadal maturity of the pomfret.

Postmortem changes in hilsa fish. Pt. 1. Studies on rigor-mortis, typical yields and protein composition of dark and white muscle of hilsa fish (Tenualosa ilisha Ham.)

Hilsa (Hilsa ilisha) caught by gill net were immediately killed by cranial spiking. Three fish were kept in ice (0°C) and three other at room temperature (33°C) to follow development of rigor mortis and changes in muscle pH. The rest were frozen stored at -20°C. Rigor started 15 minutes after death in all fish and reached full rigor (100%) state in 2 and 4 hours respectively in fish kept at 33° and 0°C. The fish at 33°C deteriorated 16 hours after while in full rigor but those at 0°C lasted 26 hours of death without deterioration. Freshly caught hilsa had a muscle pH around 7 which decreased with time rapidly at 33°C and slowly at 0°C. The relative proportion of protein fraction in white and dark muscle of fish stored at 0°C and -20°C were also studied. The proportion of dark muscle was 30.34% of the white muscle. White muscle in fish at 0°C was found to contain 32.0% sarcoplasmic, 57.6% myofibrilla, 9.4% alkali-soluble and 1.1% stroma protein whereas these proteins in dark muscle were 29.9%, 58.4%, 9.8% and 1.9% respectively. The protein fractions of white muscle in frozen-fish were found 27.6% sarcoplasmic, 64.7% myofibrilla, 6.0% alkali-soluble and 1.7% of stroma protein whereas they were 30.6%, 58.6%, 8.9 and 1.9% for dark muscle. Some changes occurred in protein composition during frozen storage. The relative amounts of sarcoplasmic, alkali soluble and stroma protein fractions decreased while myofibrilla fraction increased in frozen condition. This may be attributed to drip loss of soluble protein during thawing.

Study on fishing gears, species selectivity toward gears and catch composition of BSKB beel, Khulna, Bangladesh

An investigation on the types of fishing gear used and their species selectivity and effects on fishes of BSKB beel in Khulna was conducted from June '95 to January '96. Fishermen were found to follow 6 fishing techniques viz., netting, trapping, angling, spearing, dewatering and hand picking. Among them 23 types of the fishing gear was recorded to be used by the fishermen of which 7, 8, 4 and 4 are nets, traps, hooks and lines, and hand harpoon respectively. A total of 47 species of fish were identified in the catches of different gears used by the fishermen in BSKB beel. Particulars, mode of operation, fishing season and catch composition of different fishing gears were determined. Seine, cast and lift net, traps (charo, arinda and ghuni), and hooks and lines (dhawn and nol broshi) were recorded as nonselective gear considering the fish species caught. However, gill nets (punti, koi and fash jal), clasp nets (bhuti jal), some traps (khadom, tubo), hooks and lines (chip borshi, chasra) and all spears were used as more or less selective gear. With respect to species and its size fash jal, bhuti jal, trap (khadom, ramani), and koach, juti and jhupi among spears were regarded to be more or less large-species-gear. But punti jal, koi jal, trap (koi dughair, charo, tubo, arinda and ghuni), nol borshi and spear (ful-kuchi) were small-species-gear. Among all gears seine net, cast net, lift net, koi dughair and ramani were recorded deleterious for carps especially for stocked fingerlings. For relatively small sized wild fishes koi jal, punti jal and ghuni traps were identified as detrimental gear.

Species composition and abundance of different Macrobrachium species in a natural habitat of Kalu River near Titvala, Maharashtra State

Juveniles of freshwater prawns caught by the traditional cylindrical bamboo traps operated by the local fishermen in a natural habitat of Kalu River near Titvala were sampled every week during September to December 1991 and 1992, to study the composition and relative abundance of different species and their relationship with hydrobiological parameters. The juvenile catch comprised Macrobrachium rosenbergii, M. idella, M. scabriculum and M. bombayensis. Among these M. rosenbergii was more abundant followed by M. idella. It is also observed that high tide catches are more productive than those of low tides.

INFLUENCE OF ATMOSPHERIC COMPOSITION ON THE ABRASIVE WEAR OF TITANIUM AND Ti-6Al-4V.

A pin-on-disc apparatus has been used to investigate the wear and friction (sliding force) behavior of metals on bonded silicon carbide and alumina papers under conditions of controlled atmospheric composition. The wear rates of both commercial purity titanium and the alloy Ti-6%Al-4%V tested in air were found to remain constant with time, in contrast with the behavior of other metals tested under similar conditions, which exhibited a progressive decrease in wear rate with increasing number of passes along the same track. It is proposed that the concentration of interstitial nitrogen and oxygen in the worn metal surface, which largely determines its mechanical properties, strongly influences both the ductility of the abraded material and the force of adhesion between the metal and the abrasive particles. Parallels are drawn between abrasive wear and machining to illustrate the importance of oxygen at the interface between workpiece and tool surfaces.

Wadge Bank trawl fishery studies. Pt. 3. Nature and composition of the resident population

The demersal stock of the Wadge Bank is known to be made up of two major groups, namely the resident and migrant stocks (Sivalingam 1966b). It is necessary to analyse the two groups separately in order to correctly interpret the changes in relative abundance of the demersal fish stocks of the Bank. The object of this paper is to present the nature of the resident stock and discuss its changes in composition from 1945 to 1960. That of the migrant population will be presented later. The significance of this analysis has been discussed earlier (Sivalingam 1966a).

Fluctuations in species composition of Penaeid prawns in estuaries

During a study of the distribution of penaeid prawns in Sri Lanka waters a difference was noticed in the species composition from one estuary to another. Moreover, a marked monthly fluctuation in the relative abundance of the different penaied species was also observed. This indicated migratory behaviour. In order to study this phenomenon in the different species of prawns, regular samples of prawns were collected from two estuaries on the south-west coast of Sri Lanka, namely at Moratuwa/Panadura and at Negombo. The investigation was spread over a period of three years from 1957-1959.

The freshwater zooplankton of Sri Lanka, with a discussion of tropical freshwater zooplankton composition

Based on the study of over 500 zooplankton samples collected in Sri Lanka during 1965-1974, the species composition from different habitats is analysed. The zooplankton assemblage is typically tropical with relatively few species of Cladocera and Copepoda. The Rotifera include a large number of species of the genus Brachionus. The limnetic zooplankton resembles the pond zooplankton closely in that all the eurytopic species found in the different types of habitats, including ponds; also occur in the limnetic zooplankton. The large Cladocera belonging to the genus Daphnia are very rare. In general, large zooplankters are absent. The size composition of the zooplankton has a smaller range than in temperate regions. This is due to the absence of large-sized zooplankton species. The reasons for the differences in species variety and size composition between zooplankton of temperate and tropical regions is perhaps due to a number of factors. These include the effects of high and uniform temperatures, food availability and predation by fish and invertebrates.

The morphometrics and the proximate composition of the edible fresh water mussel Lamellidens lamellatus (Lea) from Bathalagoda tank, a man made reservoir in Sri Lanka

Morphometric characteristics of Lamellidens lamellatus were studied using a random sample of 138 individuals collected from Bathalagoda reservoir in Kurunegala district. The largest number of individuals in the collection was between 40-50 mm in length. They had a body weight between 60-80 gm. The most abundant bio-chemical component in the adductor and in the foot was protein. Carbohydrate and lipid quantities were almost equal while ash showed the least value. The total protein content ranged from 48.8% to 73.4%; the carbohydrate content from 12.64% to 23.8%; and lipid content from 12.0% to 28.1% of their dry weight. It was found that there were significant relationships between the length and the body weight; and between length and volume.

A comparative study of the morphometrics and the proximate composition of two edible molluscs Crassostrea cuculata (Born) and Perna perna (L.)

The morphometrics and the bio-chemical characteristics of Crassostrea cuculata and Perna perna were studied. In the oyster, the length was found to be positively correlated with breadth and total body weight. There was also a positive relationship between the total body weight and the total muscle weight. In the mytilid the total body weight was positively correlated with length and total muscle weight. The muscle weight was also found to be highly correlated with the length. In both animals the relationship between the length and the total body weight was curvilinear. In the oyster, the protein content was found to increase with the total body weight and the total muscle weight. In the mytilid the protein content increased not only with the total body weight but also with the length. In both animals, the relative content of protein is higher than that of carbohydrates, lipids and ash.