Future prospects and their implications for research on the ecology of freshwater fish

Abstract– Projected world population increases imply demand for an increase of 60 million tonnes on the present world fish production of 100 million tonnes. Capture fisheries are unlikely to yield more because many stocks are already overexploited, there are few remaining unexploited and management shows few signs of redressing problems. Aquaculture is a possible source of the required production, given maintenance of current rates of increase. If this potential is to be realized, the importance of maintaining the quality of freshwater, brackish and coastal marine environments can scarcely be overstated. In a world of rapid change, there is an urgent need for research at all levels of biological and social organization that relate to the ecology of freshwater fish. At the organismic level, genetics, migratory behaviour and physiological ecology will be emphasized. Population genetics research is needed to enlighten controversies concerning the impact of cultural practices and the effects of harvesting natural populations. Greater attention will be given to interactions between species, including fish and their parasites, and the dynamics of multispecies interactions in pond culture and in capture fisheries. Issues of multiple uses of water resources will force research on freshwater fish ecology into broader contexts. The march of discovery in all branches of science will have major implications for freshwater fisheries research. The next few decades will be demanding of the creative energies of young researchers.     

Effect of plant protease inhibitors on digestive proteases in two fish species, Lutjanus argentiventris and L. novemfasciatus

This work provides a comparative study of the inhibitory effect of several plant protein sources on digestive proteases of two snappers: yellow snapper (Lutjanus argentiventris) and dog snapper (Lutjanus novemfasciatus). Seed extracts did not affect gastric proteases whereas they significantly inhibit intestinal proteases. Inhibition of alkaline proteases showed that pancreatic proteases of L. argentiventris were more sensitive to seed protease inhibitors than those of L. novemfasciatus. Legume seeds showed the highest inhibitory capacity on alkaline proteases causing inhibition higher than 50% in total proteolytic activity. Protease inhibition on digestive extracts was assessed using different relative concentration of seed extracts and represented by constructing dose response curves. In order to reduce the inhibitory effect, seed extracts were acid-treated before the inhibition assay. Results showed that acid treatment did not affect the inhibitory capacity of seeds on alkaline proteases in both species. However, when the action of gastric enzymes was simulated on seed extracts, the inhibitory capacity was reduced significantly, mainly in the case of L. novemfasciatus. The responses of fish enzymes to heat-treated seed extracts were also tested. Only higher temperatures were capable of reducing the inhibitory capacity of seed, with the specific response to the snapper species. The use of biochemical assays allows us to quantify the action of inhibitors on total proteolytic activity. In addition, zymograms obtained by substrate-SDS-PAGE provided qualitative information about the number and type of proteases affected by each inhibitor. Each seed extract produces a characteristic profile of inhibition on alkaline protease. The results obtained are important for future formulation of feeds for these snapper species.     

Current status of the giant freshwater prawn ( Macrobrachium rosenbergii) industry in China,with special reference to live transportation

The giant freshwater prawn Macrobrachium rosenbergii was first introduced into mainland China by the Chinese Academy of Agricultural Sciences from Japan in 1976. It was cultured at the Guangdong Province Fishery Institute (now as Pearl River Fishery Institute, Chinese Academy of Fishery Sciences). Following these early efforts, giant freshwater prawn culture has gradually spread to northern and inland areas. At this time (2011), China has become the largest producer of giant freshwater prawn in the world. Due to a preference of cooking with fresh aquatic products, Chinese retail markets have developed which have special live‐holding counters. From small rural shops to urban supermarkets and specialty restaurants, live seafoods are commonly available whereby customers pick out the products they wish to purchase and consume. Giant freshwater prawns are produced in over 35 countries throughout the world. They are usually sold either fresh, on‐ice, or frozen. What makes the Chinese prawn industry unique is its focus on a live transportation and marketing model. As a result, numerous innovative live‐transport technologies have been developed which have been key to the success of this expanding domestic industry. In this article, we would like to give a general overview of the giant freshwater prawn industry, its status in China, and the special role live‐transportation has for expanding production of giant freshwater prawns.     

Screening for organic acids in fish tissues with special reference to the distribution of taurine inRutilus rutilus L.

A liquid chromatographic method for rapid profiling of some organic acids and other compounds of physiological interest in fish tissues is presented. The method provides the detection of -ketoglutaric, malic and pyruvic acid and is optimized for the quantitation of citric, phosphoric, succinic, lactic and fumaric acids, as well as glucose and especially taurine. These substances were separated in a single analytical run on a cation exchange column with dilute sulfuric acid as the elutant. The effluent was monitored by a refractive index or an UV detector at 208 nm wavelength. Resolution was satisfactory. No further treatment was found to be necessary when samples were deproteinized with perchloric acid. Taurine (2-aminoethansulfonic acid), not previously described in the roach (Rutilus rutilus L.), occurs in considerable amounts in red and white muscle and heart tissue. However, it is also present in all other tissues.     

The occurrence of different forms of ovarian cysts in swine with special reference to their effect on the estrus cycle]

Ovaries of 100 sows with ovarian cysts were collected at the slaughterhouse after normal slaughter. The ovarian function was assessed macroscopically and representative sections of 55 ovaries were examined histologically. The cysts were grouped into the following categories: follicle theca cysts, follicle lutein cysts, lutein cysts, blood cysts and mixed forms with concurrent incidence of the above cyst forms. Only follicle theca cysts, follicle lutein cysts, lutein cysts or blood cysts were found in 24%, 7%, 32% and 10% of animals, respectively. In 27% of animals the above mentioned forms of cysts occurred concurrently. A large number of cysts per animal was found for follicle theca cysts (9.0 cysts per animal) and mixed forms (11.0 cysts per animal). Follicle lutein cysts, lutein cysts and blood cysts were developed in smaller numbers (3.1, 3.9 and 4.8 cysts per animal, respectively). Anestrus occurred only for follicle theca cysts, if their number exceeded 7 cysts per animal (13 per cent of the examined animals). Blood cysts occurred only during the metoestrus and follicle lutein and lutein cysts only during the corpus luteum phase. It is assumed that the cysts regress after the 13th day of the cycle, if normal corpora lutea are present at the same time. Only follicle theca cysts occurring in large numbers persist and block subsequent cyclic activity. There seems to be a particular predisposition for the development of cysts when the ovarian cycle is re-initiated after anestrus.     

The nutrient status of the agriculturally impacted Gamtoos Estuary,South Africa,with special reference to the river‐estuarine interface region (REI)

• 1. Ecological water reserves are part of the new water management philosophy in South Africa. The estuaries are threatened by excessive water abstraction from their rivers and the consequent reduction in freshwater input. This study was conducted to further improve our understanding of freshwater requirements in terms of nutrients for South African estuaries.
• 2. The Gamtoos Estuary was sampled between November 1996 and November 1998 to determine its nutrient status and freshwater input rates. Furthermore, the possible existence of a distinct river‐estuarine interface (REI) in terms of nutrients has been investigated. Nutrients analysed included phosphate, nitrate, nitrite, ammonia, dissolved organic nitrogen (DON), dissolved organic carbon (DOC), particulate organic nitrogen (PON) as Kjieldahl nitrogen, total particulate phosphorus and total particulate carbon.
• 3. The Gamtoos River was found not to be the ultimate source of nutrients to the estuary, but non‐point sources such as the seepage of fertilisers from adjacent agricultural fields determined to a great extent the nutrient status of the estuary.
• 4. Results showed that it was not possible to identify a defined river‐estuarine interface region for all nutrients. Most were measured in higher concentrations in the lower salinity reaches (<17‰) where we observed the combined effect of inputs from the Gamtoos River, an agricultural drainage pipe, and fertilizer seepage from non‐point sources on nutrient concentration.
• 5. Prolonged water withdrawal for human use impacts the continuous renewal of the nutrient pool so important to other South African estuaries with relative pristine catchment areas. However, reduced fresh water inputs could enhance eutrophication in polluted estuaries due to a decreased flushing potential of the estuary. In this case the Gamtoos Estuary has a freshwater requirement for freshets and floods to “clean” the estuary of accumulated nutrients and other organic material.
• 6. This should be a consideration in further freshwater abstraction policies. Conservation issues arise since the Gamtoos Estuary is one of the few permanently open estuaries along the South African coast and serve in this study as an example and as a first attempt to relate freshwater requirements to nutrient dynamics in a South African context.

Copyright © 2002 John Wiley & Sons, Ltd.     

Gill morphometry of the facultative air-breathing loricariid fish,Hypostomus plecostomus (Walbaum) with,special emphasis on aquatic respiration

Gill respiratory surface area and oxygen consumption during aquatic respiration were measured in the facultative air-breathing loricariid fish,Hypostomus plecostomus. The fish did not surface to breathe atmospheric air in normoxic water; air-breathing was evoked by environmental hypoxia (water oxygen tension=35±2, mmHg) and did not show size-related threshold differences for air breathing.During gradual hypoxia, without access to atmospheric, air,H. plecostomus was found to be an oxyregulator and showed a reduced range of water oxygen tension in which the oxygen consumption remained constant in smaller fish. The critical oxygen tensions were 55 and 33 mmHg at 25°C for fish of 14–30 g and 31–80g body weight, respectively.The gill respiratory surface area (total lamellae area) is reduced, however, the lamellar frequency per mm of gill filament is high which facilitates the gas exchange. Moreover, the increase of gill respiratory surface area (b=0.666) is higher than the increase in routine VO₂ (b=0.338) showing a positive relationship between the gill respiratory surface area /VO₂ ratio and body mass (b=0.328); this indicates that the fish have greater gill respiratory surface area per unit of routine VO₂ as they grow.     

Growth and feeding responses of the mutton snapper,Lutjanus analis (Cuvier 1828), fed on diets with soy protein concentrate in replacement of Anchovy fish meal

This study evaluated the growth (first phase) and feeding responses (second phase) of juvenile mutton snapper fed four isonitrogenous and isoenergetic diets with increasing levels of soy protein concentrate (SPC) in substitution to fish meal (FM). The FM was replaced by SPC at 0% (basal diet, SPC000), 33% (SPC130), 57% (SPC214) and 77% (SPC300). After 95 days of rearing, fish fed SPC300 attained a significantly lower body weight (54.9 ± 13.2 g) compared with those fed diets SPC000, SPC130 and SPC214 (76.5 ± 14.0 g, 73.9 ± 13.8 g and 70.5 ± 14.0 g respectively). Fish yield increased significantly from 891 ± 36 g m^?3 for fish fed SPC300 to an average of 1099 ± 111 g m^?3 for other diets. A maximum fish body weight gain of 0.60 ± 0.05 g day^?1 and a maximum specific growth rate of 1.47 ± 0.07% day^?1 were achieved for SPC000. Behavioural assays conducted during 10 days revealed the loss in fish growth with diets containing higher levels of SPC was due to a decline in feed intake. Low feed intake driven by a poor feed palatability appeared to have been a major obstacle against higher inputs of SPC in diets for mutton snapper.     

Potential effects of global climate change on fisheries in the Trasimeno Lake (Italy), with special reference to the goldfish Carassius auratus invasion and the endemic southern pike Esox cisalpinus decline

Global climate changes have led to a gradual warming of the planet, resulting in decreased precipitation and rising temperatures in Mediterranean inland waters. In Trasimeno Lake, the largest shallow lake in Italy, some non‐native fish species have probably benefited from these changes as they are thermophilic and characterised by wider habitat preferences. Fish data collected by gillnets and fyke nets between 1956 and 2016, and by electrofishing in 1993 and 2014, were used to analyse changes over time in the fish community in relation to environmental conditions. An explosion in goldfish Carassius auratus (L.), following its introduction in 1988, coupled with water level fluctuations and reduced transparency, contributed to the reduction in commercial fish catch in the lake, and to the decline of the endemic southern pike Esox cisalpinus Bianco & Delmastro, already threatened by reduced spawning habitat and interspecific competition with other non‐native predatory fishes.     

Distribution of jack mackerel (Trachurus japonicus) larvae and juveniles in the East China Sea, with special reference to the larval transport by the Kuroshio Current

Horizontal distribution patterns of jack mackerel (Trachurus japonicus) larvae and juveniles were investigated in the East China Sea between 4 February and 30 April 2001. A total of 1549 larvae and juveniles were collected by bongo and neuston nets at 357 stations. The larvae were concentrated in the frontal area between the Kuroshio Current and shelf waters in the upstream region of the Kuroshio. The abundance of small larvae (<3 mm notochord length) was highest in the southern East China Sea (SECS) south of 28°N, suggesting that the principal spawning ground is formed in the SECS from late winter to spring. Jack mackerel also spawned in the northern and central East China Sea (NECS and CECS, respectively), as some small larvae were also collected in these areas. In the SECS, the abundance of small larvae was highest in February and gradually decreased from March to April. The habitat temperature of small larvae in the SECS and CECS (20–26°C) was higher than that in the NECS (15–21°C), suggesting higher growth rates in the SECS and CECS than in the NECS. The juveniles (10‐ to 30‐mm standard length) became abundant in the NECS off the west coast of Kyushu Island and CECS in April and were collected in association with scyphozoans typical of the Kuroshio waters. However, juveniles were rarely collected in the SECS, where the small larvae were concentrated. Considering the current systems in the study area, a large number of the eggs and larvae spawned and hatched in the SECS would be transported northeastward by the Kuroshio and its branches into the jack mackerels’ nursery grounds, such as the shallow waters off the west coast of Kyushu and the Pacific coast of southern Japan.     

Evolution of body composition of European eels during their growth phase in a fish farm, with special emphasis on the lipid component

The effects of changes in the feeding regime on growth rate, body composition and fatty acid content of body lipids were monitored during the production cycle of European eels (Anguilla anguilla) in a fish farm, from elvers to commercial size (> 100 g).A high variation in growth rate obliged periodic grading. The fat content in the body of the eels notably increased over the study period in a direct relationship with size. At commercial size, a certain degree of sexual dimorphism was apparent, as were differences in dorsal coloration. At this stage, females were clearly larger than males and had a greater amount of body fat.Changes in dietary lipid composition (moist natural food, pellet foods with low and high fat content) influenced fatty-acid composition of body and muscle lipids. No differences between sexes were recorded in this respect. In general, indices of the nutritional quality of body lipids decreased progressively (in terms of the ratio between saturated, on the one hand, and mono- and polyunsaturated, on the other). However, the high fat content of the eels' edible fraction provides an equally high amount of the strongly recommended highly unsaturated fatty acids of the 3 series (HUFA3). © Rapid Science Ltd. 1998     

Effects of substituting dietary fish oil with crude palm oil and palm fatty acid distillate on growth,muscle fatty acid composition and the activities of hepatic lipogenic enzymes in snakehead (Channa striatus,Bloch 1793) fingerling

Three diets were formulated to be iso‐nitrogenous (450 g kg^?1), iso‐lipidic (65 g kg^?1) and iso‐energetic (18.5 KJ g^?1), varying only in their lipid sources and designated as 100% fish oil (FO), 100% crude palm oil (CPO) and 100% palm fatty acid distillate (PFAD). Feed were hand fed to homogenous groups of 12 Channa striatus fingerlings (mean weight 3.5 ± 0.3 g) per tank in triplicate for 12 weeks, in a recirculation system. The growth performance and feed intake in the CPO and PFAD treatments were significantly (P<0.05) higher than those in the fish fed the control diet (FO), respectively, whereas the feed conversion ratio was better in PFAD than that in the other treatments respectively. The biological indices monitored (hepatosomatic index and viscerosomatic index) as well as carcass yield did not vary significantly among all the treatments respectively. The muscle fatty acid (FA) profile of fish was influenced by the composition of the diets fed, whereas no differences were recorded in the activities of the hepatic lipogenic enzymes monitored (fatty acid synthetase, citrate cleavage enzyme and malic enzyme). Whole‐body proximate composition analysis revealed that PFAD treatment, compared with others, contained significantly higher protein and ash, but lower lipid contents, although the muscle content of these nutrients was similar among all the treatments. Based on the results of this trial, CPO and PFAD could be used to partially substitute FO in the diet for C. striatus fingerling, to achieve good growth performance without any negative effects or compromising the muscle n‐3 FA composition (especially in the docosa hexaenoic acid and eicosa pentaenoic acid content).     

Effects of body size and water temperature on food consumption and growth in the sea cucumber Apostichopus japonicus (Selenka) with special reference to aestivation

To investigate the effects of body size and water temperature on feeding and growth in the sea cucumber Apostichopus japonicus (Selenka), the maximum rate of food consumption in terms of energy (C_maxe; J day^?1) and the specific growth rate in terms of energy (SGRe; % day^?1) in animals of three body sizes (mean±SE) – large (134.0±3.5 g), medium (73.6±2.2 g) and small (36.5±1.2 g) – were determined at water temperatures of 10, 15, 20, 25 and 30°C. Maximum rate of food consumption in terms of energy increased and SGRe decreased with increasing body weight at 10, 15 and 20°C. This trend, however, was not apparent at 25 and 30°C, which could be influenced by aestivation. High water temperatures (above 20°C) were disadvantageous to feeding and growth of this animal; SGRe of A. japonicus during aestivation was negative. The optimum temperatures for food consumption and for growth were similar and were between 14 and 15°C, and body size seemed to have a slight effect on the optimal temperature for food consumption or growth. Because aestivation of A. japonicus was temperature dependent, the present paper also documented the threshold temperatures to aestivation as indicated by feeding cessation. Deduced from daily food consumption of individuals, the threshold temperature to aestivation for large and medium animals (73.3–139.3 g) was 24.5?25.5°C, while that for small animals (28.9–40.7 g) was between 25.5 and 30.5°C. These values are higher than previous reports; differences in sign of aestivation, experimental condition and dwelling district of test animals could be the reasons.