A study on the average yield of different species pf prawns used for freezing and canning

The paper deals with the average yield of four spp of prawns viz. Metapenaeus dobsoni, Metapenaeus affinis, Parapenaeopsis stylifera and Penaeus indicus on conversion to peeled and deveined (PD), cooked and peeled (CP) and head less shell on (HL) forms in the different months of a year and the likely variations observed in the average yield.

A wider choice of construction materials for the modern fishing boats

An account of fishing vessel construction materials is given, with information on essential features, and a material account. Materials discussed in detail are steel, wood, aluminium, glass reinforced plastic, and ferro-cement.

Problems associated with the over protection of fishing trawlers against sea water corrosion and fouling

Some presently used anti-fouling materials contain metals and other compounds, which are toxic in the environment. Coating products are not always stable, and there is a resulting pollution hazard. In particular if surfaces are poorly prepared and manufactures' instructions are not closely followed the application of anti-fouling substances becomes pointless and dangerous. In addition the salinity, constant biological activity and suspended particles make seawater a highly corrosive material in its own right.

Studies on phenolase enzyme in prawns. II. The inhibitory action on the enzyme by certain chemical agents

The effect of certain chemical agents on dopa oxidation by phenolases has been examined. Sulphur containing amino carboxylic acids are inhibitory agents for dopa oxidation. Tyrosine, a substrate for the enzyme also acts as an inhibitor for dopa oxidation by the enzyme. The possible mode of action has been discussed. The function of diethyl dithiocarbamate in suppressing the display of enzyme activity has been detailed and its behaviour has been compared to the other chemical agents studied.

Abalone R&D at AQD

Details are given of the results of research conducted at the SEAFDEC Aquaculture Department on abalone (Haliotis asinina). The following areas are covered: reproductive biology; induced spawning; raising abalone in the hatchery; and, cage culture trials.

The status and significance of invertebrate communities

Invertebrates constitute a major link in energy flow culminating into fish production in aquatic ecosystems. In tropical water bodies relatively little research has been done on invertebrate ecology especially their role in fishery production. European scientists through periodic expeditions to Africa in the last quarter of the 20th century carried out the earliest research on zooplankton. Rzoska (1957) listed these early workers including Stuhlmann (1888), Weltner (1897) and Mrazek (1897-1898). Daday (1907), Verestchagin (1915) and Delachaux (1917) undertook further work during the early twentieth century. These earlyworks provide a useful basis for tracking community changes by comparison with modem investigations. Worthington (1931) provided the first quantitative account of the zooplankton of Lake Victoria along with information on diurnal vertical migrations, compared to a temperate lake. The establishment of the East African Freshwater Fisheries Research Organisation (EAFFRO) at Jinja in 1947 enabled investigations on the fisheries, algae, invertebrates and water quality aspects of the lake (EAFFRO Annual Reports 1947-1977) to be regularly carried out. Macdonald (1956) made the first detailed observations on the biology of chaoborids and chironomids (IakefJies) in relation to the feeding of the elephant snout fish, Mormyrus kannume. A detailed study of the biology of the mayfly, Povilla adusta Navas with special reference to the diurnal rhythms of activity was carried out by Hartland-Rowe (1957). The search to unravel the ecological role of aquatic invertebrates in the production dynamics of the lake has taken invertebrate research to greater heights through recent investigations including Okedi (1990), Mavut

Marine Vertebrates and Low Frequency Sound: Technical Report for LFA EIS

Over the past 50 years, economic and technological developments have dramatically increased the human contribution to ambient noise in the ocean. The dominant frequencies of most human-made noise in the ocean is in the low-frequency range (defined as sound energy below 1000Hz), and low-frequency sound (LFS) may travel great distances in the ocean due to the unique propagation characteristics of the deep ocean (Munk et al. 1989). For example, in the Northern Hemisphere oceans low-frequency ambient noise levels have increased by as much as 10 dB during the period from 1950 to 1975 (Urick 1986; review by NRC 1994). Shipping is the overwhelmingly dominant source of low-frequency manmade noise in the ocean, but other sources of manmade LFS including sounds from oil and gas industrial development and production activities (seismic exploration, construction work, drilling, production platforms), and scientific research (e.g., acoustic tomography and thermography, underwater communication). The SURTASS LFA system is an additional source of human-produced LFS in the ocean, contributing sound energy in the 100-500 Hz band. When considering a document that addresses the potential effects of a low-frequency sound source on the marine environment, it is important to focus upon those species that are the most likely to be affected. Important criteria are: 1) the physics of sound as it relates to biological organisms; 2) the nature of the exposure (i.e. duration, frequency, and intensity); and 3) the geographic region in which the sound source will be operated (which, when considered with the distribution of the organisms will determine which species will be exposed). The goal in this section of the LFA/EIS is to examine the status, distribution, abundance, reproduction, foraging behavior, vocal behavior, and known impacts of human activity of those species may be impacted by LFA operations. To focus our efforts, we have examined species that may be physically affected and are found in the region where the LFA source will be operated. The large-scale geographic location of species in relation to the sound source can be determined from the distribution of each species. However, the physical ability for the organism to be impacted depends upon the nature of the sound source (i.e. explosive, impulsive, or non-impulsive); and the acoustic properties of the medium (i.e. seawater) and the organism. Non-impulsive sound is comprised of the movement of particles in a medium. Motion is imparted by a vibrating object (diaphragm of a speaker, vocal chords, etc.). Due to the proximity of the particles in the medium, this motion is transmitted from particle to particle in waves away from the sound source. Because the particle motion is along the same axis as the propagating wave, the waves are longitudinal. Particles move away from then back towards the vibrating source, creating areas of compression (high pressure) and areas of rarefaction (low pressure). As the motion is transferred from one particle to the next, the sound propagates away from the sound source. Wavelength is the distance from one pressure peak to the next. Frequency is the number of waves passing per unit time (Hz). Sound velocity (not to be confused with particle velocity) is the impedance is loosely equivalent to the resistance of a medium to the passage of sound waves (technically it is the ratio of acoustic pressure to particle velocity). A high impedance means that acoustic particle velocity is small for a given pressure (low impedance the opposite). When a sound strikes a boundary between media of different impedances, both reflection and refraction, and a transfer of energy can occur. The intensity of the reflection is a function of the intensity of the sound wave and the impedances of the two media. Two key factors in determining the potential for damage due to a sound source are the intensity of the sound wave and the impedance difference between the two media (impedance mis-match). The bodies of the vast majority of organisms in the ocean (particularly phytoplankton and zooplankton) have similar sound impedence values to that of seawater. As a result, the potential for sound damage is low; organisms are effectively transparent to the sound – it passes through them without transferring damage-causing energy. Due to the considerations above, we have undertaken a detailed analysis of species which met the following criteria: 1) Is the species capable of being physically affected by LFS? Are acoustic impedence mis-matches large enough to enable LFS to have a physical affect or allow the species to sense LFS? 2) Does the proposed SURTASS LFA geographical sphere of acoustic influence overlap the distribution of the species? Species that did not meet the above criteria were excluded from consideration. For example, phytoplankton and zooplankton species lack acoustic impedance mis-matches at low frequencies to expect them to be physically affected SURTASS LFA. Vertebrates are the organisms that fit these criteria and we have accordingly focused our analysis of the affected environment on these vertebrate groups in the world’s oceans: fishes, reptiles, seabirds, pinnipeds, cetaceans, pinnipeds, mustelids, sirenians (Table 1).

Biological observations in Indian mackerel, Rastrelliger kanagurta (Cuvier) 1816, (Pisces: Scombridae) from East African waters

The present study was under taken to provide further and more detailed information on the apparent seasonal and relative abundance of the species, food and feeding habits. Spawning season and size composition. The incidence of parasites, in relation to the month of the year and the fish length, was also examined.

Preliminary observations on cage culture of Tilapia esculenta Graham and Tilapia xillii (Gervais) in Lake Victoria waters, at the Freshwater Fisheries Institute, Nyegezi, Tanzania

Cage culture of Tilapia is not suggested as a substitute for any known techniques in fish culture, but as one of the various techniques of obtaining more fish under controlled conditions. This fact has been very well accepted in various countries. Whererever facilities exist, this line of fish culture should be vigorously explored as a possible avenue in increasing fish production. High density stocking, management under controlled conditions, easy technique of fabricating the cage at relatively low cost, having no demand on land area, absence of prolific and effective breeding and easy availability of fish when a person needs it are a few of the attractions of the technique. The studies indicate that it is desirable to have different meshes for the cages, such as, small meshed cages for rearing fry to fingerlings stages, and larger meshed cages for rearing fingerlings to table sized fishes. II' the meshes are small, the resistance will be more and less water wilt pass through. While feeding with powdered food material, because of brisk activity of feeding fish, a part of the feed appeared wasted. This can be easily overcome if we would resort to feeding fish with cheap pelleted feeds which will no doubt reduce wastage. Precaution has to be taken against damage of the net and thereby loss of fish and against poaching by unauthorised persons. In the present attempt has been demonstrated the possibility of utilizing locally available species of Tilapia for cage culture and obtaining moderately satisfactory growth rates.

Growth rates of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) under cultivation in ponds at Nyegezi, Tanzania

Aquaculture in Tanzania is still on a subsistence level and most of the ponds are maintained as part time job. The ponds are too small, shallow and over crowded with stunted Tilapia spp. In the present paper the results of experiments conducted in ponds at Nyegezi with T. esculenta and T. zillii are presented. This was part of an overall project of developing techniques of fish cultures with Tilapia under the limited existing conditions at Nyegezi. In a mono - species culture experiement with Tilapia zillii in nine month's time an average size of 172.8 mm/115.0 g was attained. In another experiment with T. zillii and T. esculenta in thirteen month's time, T. zillii attained an average size of 180.2mm/106.6 g and T. esculenta 193.6 mm/118.8 g. In another experiment with intensive feeding schedule an average size of 179.3 mm/126.6 g was attained by T. zillii and 191.0 mm/125.0 g by T. esculenta in four month's time. A locally prepared supplimentary feed with local Brewery Waste and Fish Meal (10:1) was readily accepted by both species of Tilapia. T. zillii voraciously fed on Cabbage leaves, Cauliflower leaves, Chinese cabbage leaves, Cassava leaves and on the common weed Comalina sp. Though all the items mentioned above were readily accepted by T. zillii feeding with Comaltna sp. was the easiest and most convenient because of its availability. In an intensive feeding experiment with vegetable leaves/Comalina sp. and the locally prepared supplimentary feed the fishes attained table size in four months time. Cement cistens of 5 X 3 X 1½ m size could be conveniently used for breeding both species of Tilapia. T. zillii had semi adhesive eggs and they were deposited on the sides of the cement wall. The number of young ones in a brood ranged from 160 to 314 in T. esculenta and 687 to 4,356 in T. zillii.

Hybridization between Tilapia zillii (Gervais) and Tilapia andersonii (Casteinau) at the Freshwater Fisheries Institute, at Nyegezi, Tanzania

As a part of an overall project on fishculture development techniques in Tanzania, hybridization between Tilapia zillii and Tilapia andersonii was carried out at the Freshwater Fisheries Institute, Nyegezi, Tanzania. T. andersonii, a plankton feeder, is not indigenous to Tanzania but was introduced in 1968 from Zambia for certain specific purpose. T. zillii, a macrovegetation feeder, is present locally and is common. In the present studies T. zillii (245.0 mm/260.0 g) female was hybridized with T. andersonii (288.0 mm/350.0 g) male. Under cement cistern conditions it was only after about four months of acclimatization that hybridization between the two occurred. About 1,637 interspecific hybrid fry were produced in a single brood. Eggs were adhesive and parental care shown by the female, the male being driven away. Growth under cistern conditions was slow, attaining a size of 134.8 mm/44.3 g in 10 months. But this growth rate need not be taken as ideal. In body shape, colouration and other morphometric characters the hybrids had inherited from both parents. The number of gill rakers among the hybrids was eighteen which was intermediate between T. zillii (12) and T. andersonii (27). Among one hundred and seventy two specimens (106.0 mm - 168.0 mm) cut and examined the sex ration was hundred per cent males and all of them were between II and IV stages of maturity. This is the first report of fish hybridization from Tanzania and possibly the first report on hybridization between T. zillii and T. andersonii. The full significanoe of the findings and its role in African fishculture is discussed.

Experimental fisheries resource survey of Lake Wamala: Annual report 1975

During 1975, two experimental fisheries resource surveys were conducted on lake wamala from 14th to 20th May and 10th to 16th July. The purpose of the experimental fishing on this lake was to provide information required to genrate enough scientific guidelines and advice for rational exploitation, management, development and utilization of the fishery resources in the lake.