Food Source For Fish Research Articles

Territorial behavior of threespot damselfish (Eupomacentrus planifrons) increases reef algal biomass and productivity

Algal growth and damselfish (Eupomacentrus planifrons) territories were studied in two reef habitats at Discovery Bay, Jamaica. Damselfish territories were contiguous in the reef flat (0 to 2.5 m), where the algal composition and biomass varied from territory to territory. In contrast, on the lower reef terrace (22 m), damselfish territories were often spatially segregated. While the algal composition of the territories was more uniform on the reef terrace, the total algal biomass was lower than in the territories on the reef flat. Damselfish are largely herbivorous, and they defend their territories against most intruding fish, including a number of herbivorous species. Areas of the reef terrace outside of damselfish territories were heavily grazed by herbivorous fishes and contained only small quantities of non-crustose algae. The reef terrace territories were characterized by a multispecific turf of algae (greens, blue-greens, and reds) covering the Acropora cervicornis framework and by the leafy, brown alga, Lobophora variegata. A rapid reduction in the biomass of brown algae and filamentous algae was noted when damselfish were permanently removed from their territories. Only calcified, encrusting algae — plants apparently somewhat undesirable as fish food sources — would be common on the terrace zone of this reef if damselfish territories were absent. Damselfish territoriality may significantly influence the dynamics of some reefs by increasing the biomass of the algal turf thereby increasing; reef productivity. Since blue-green algae, potential nitrogen fixers, occur in these algal turfs, the fish may also be indirectly affecting reef nutrition.

The Drift of Stream Insects

The drift of stream insects and other invertebrates refers to their down­ stream transport in stream currents. While stream invertebrates are adapted by various means for maintaining their position in running waters, it is to be expected that the occasional individual will lose its altachmeIt or orien­ tation to its substrate and drift downstream. However, it IS onlywithin the last 20 years that observations have been made of large number§-of aquatic insects in the drift. The quantities have been large enough to bring into question the stream's productive capacity to withstand such a high rate of attrition and the possible necessity for an upstream return of some kind. Furthermore, it has interested many ecologists that the drift usually occurs in some type of diel periodicity. and that probably d�adian rhythms are involved. It should be emphasized at the beginning that a drif�--fauna, as distinct from the bottom fauna, does not exist and is, in fact, an inappropriate term. Drifting is merely a temporary event in the life of many members of the bottom fauna or other substrate-oriented populations. Among the earliest studies on invertebrate drift were those of Needham in 1928 (84), who was primarily concerned with the drift of terrestrial in­ sects that fell onto the stream surface, as a fish food source. But, in captur­ ing these organisms with a net stretched across a small stream, he also col­ lected drifting aquatic forms. Several other investigations on drift were completed in the next two decades, leading to the conclusion that a continu­ ous drift of invertebrates must be considered a natural feature of streams (18, 19, 50, 59). Subsequent investigations, both in the United States and Europe, revealed the presence of large quantities of invertebrates in the drift (5, 42). But the contribution having perhaps the greatest impact in stimulating interest and research into the subject was published in 1954 by Miiller on the drift in north Swedish streams (74). In this work, Miiller also reported large quantities, even in a very small stream, and made obser­ vations on the qualitative relationships among drift, the bottom fauna, and

Der gegenwärtige Stand der Züchtungsforschung an Meeresfischen in Japan

1. The present status of marine fish cultivation research in Japan is reviewed. 2. In marine fish farms, the stocks have been recruited from young fish caught at sea, but recently, artificially reared fry are more and more taking the place of natural young fish, in some species. 3. The main fish species cultivated in Japanese farms are yellow-tailSeriola quinqueradiata, pufferFugu rubripes rubripes and red sea breamPagrus major; they are mostly cultivated in floating net cages set in sheltered places. 4. To increase the natural resources, the release of artificially reared young of some fishes has just started in the Inland Sea of Japan. 5. Efforts are being made to obtain ripe eggs from reared marine fishes, to hatch fertilized eggs and to raise fry: Spawning, fertilization, hatching and raising to commercial size has been achieved in several important shallow water marine fishes. 6. To keep the ambient water suitable for hatching and raising of fishes, filtration, circulation, exchange of sea water and availability ofChlamydomonas sp. andChlorella sp. (to remove metabolic wastes of the fish and to supply oxygen) have been studied. 7. Research on food sources suitable for respective stages of fishes and on the methods of producing such foods have been made. Several marine organisms are cultivated in abundance as food sources for fishes. 8. Diseases of marine fishes have been studied to keep them healthy and to enhance survival rates. 9. Some experiments on the production of hybrids between different marine fish species are now in progress; several hybrids have already been produced artificially and reared successfully.

The food of a community of East African freshwater fishes

Quantitative data on the food of the fishes inhabiting Lake Mcllwaine, Rhodesia, show that the feeding of the dominant species in this community (Clarias gariepinus (Burchell), Hydrocynus vittatus (Castelnau), Tilapia melanopleura Dumeril, Tilapia mossamhica Peters, Tilapia macrochir Boulenger, Labeo altivelis Peters, and Gnathonemus macrolepidotus (Peters)) covers a wide spectrum, and almost all elements of the potential food supply are utilized. Exceptions are noted, however, and the introduction of the Indian carp, Catla catla (Cuv. & Val.), is advocated in order to utilize the large blooms of phyto‐ and zooplankton. The oligochaete, Branchiura cf. sowerbyi, which forms over 50% of the benthic biomass is also not utilized as a source of fish food. However, no fish species is known to feed on oligochaetes to any large extent. Predation by the Tigerfish, Hydrocynus vittatus, is shown to have severe effects upon recruitment to the valuable Tilapia fishery, and the reduction of the abundance of H. vittatus by means of selective fishing techniques is advocated.

The food of a community of East African freshwater fishes

Quantitative data on the food of the fishes inhabiting Lake Mcllwaine, Rhodesia, show that the feeding of the dominant species in this community (Clarias gariepinus (Burchell), Hydrocynus vittatus (Castelnau), Tilapia melanopleura Dumeril, Tilapia mossamhica Peters, Tilapia macrochir Boulenger, Labeo altivelis Peters, and Gnathonemus macrolepidotus (Peters)) covers a wide spectrum, and almost all elements of the potential food supplyare utilized. Exceptions are noted, however, and the introduction of the Indian carp, Catla catla (Cuv. & Val.), is advocated in order to utilize the large blooms of phyto‐ and zooplankton. The oligochaete, Branchiura cf. sowerbyi, which forms over 50% of the benthic biomass is also not utilized as a source of fish food. However, no fish species is known tofeed on oligochaetes to any large extent. Predation by the Tigerfish, Hydrocynus vittatus, is shown to have severe effects upon recruitment to the valuable Tilapia fishery, and the reduction of the abundance of H. vittatus by means of selective fishing techniques is advocated.

XVIII.—The Benthic Amphipoda of the North-Western North Sea and Adjacent Waters

The order Amphipoda, of the Crustacea Malacostraca, which consists of the 3 sub-orders Hyperiidea, Gammaridea, and Caprellidea, is highly important in the economics of the sea as a source of fish food. Hyperiids figure prominently in the diet of species which feed pelagically. Hardy (1924), for example, found them amongst the principal items in the food of East Anglian herring. Gammarids are preyed upon by bottom feeders in general. Todd (1905, 1907) and Blegvad (1916) record them in varying percentages from the stomachs of adult cod, haddock, whiting, plaice, dabs, flounders, sole, and skate. Their chief importance, however, would seem to be in the diet of fishes in post-larval and adolescent stages. Todd (1907, 1914) found Gammarids the main support of cod under 15 cm. and of plaice and dabs under 10 cm. Blegvad (1930) states that in Danish waters, plaice in their first year feed almost exclusively upon them. Clark (1922) found that in the early stages of 4 species of skate, Amphipods occurred in from 50 to 84 per cent of the stomachs examined, and Steven (1930) found the food of young stages of R. clavata and R. maculata to consist chiefly of Gammaridea. Gammarid species, as recorded by Hunt (1924), are also eaten by a variety of bottom-dwelling invertebrates.