An evaluation of the role and impacts of alien finfish in Asian inland aquaculture

Asia dominates global aquaculture production accounting for over 80% of the total and the mainstay in Asian aquaculture is finfish. Over the years, Asia has experienced a number of inter‐continental and intra‐continental transfers/introductions/translocation of finfish species, between nations and watersheds, beyond their natural range of distribution, primarily for aquaculture development. In this article all such species are referred to as alien species. An attempt is made to evaluate the importance of the production of alien species in selected Asian nations, using statistics of the Food and Agriculture Organization. Also, negative effects, if any, based on literature surveys, of alien species in relation to displacement of indigenous species, and on biodiversity and/or genetic diversity together with associated pathogen transfers are evaluated. The major alien species, based on their significance to Asian inland aquaculture considered, are the tilapias, catfish, Chinese and Indian major carps and common carp. It is estimated that currently alien species account for nearly 12% of the cultured finfish production (2.6 million tonnes) in Asia, valued at US$ 2.59 billion, and the contribution exceeds 40% when Asian countries excluding China are taken into consideration. Inland finfish aquaculture in some Asian nations, such as Indonesia and the Philippines, is predominated by alien species, and in some others, e.g. Bangladesh and India, the contribution from alien species has been increasing steadily. It is suggested that overall alien finfish species have done little ecological harm to native flora and fauna. However, in the wake of increasing anthropogenic development taking place in watersheds the resulting environments are often made unconducive to indigenous species but not to some alien species, thereby potentially and indirectly making the latter invasive.     

The effect of dietary protein level on pond water quality and feed utilization efficiency of pacúPiaractus mesopotamicus (Holmberg, 1887)

The effect of supplemental feeds with different levels of crude protein on pond water quality and food utilization efficiency by pacú (Piaractus mesopotamicus) was evaluated in a semi‐intensive culture system. Fish were stocked at a density of one individual per m², raised for 299 days, and fed isocaloric diets containing soybean meal, blood and bone meal, and yellow maize. Dietary treatments consisted of diets containing 25%, 35%, and 45% crude protein. Ponds receiving the two highest protein levels showed significantly higher values of alkalinity, conductivity and nitrites. High dietary protein diets resulted in no significant improvements in final weight (336.4±77.2, 308.2±92.6 and 368.4±82.2 g, mean±standard deviation, for 25%, 35% and 45% protein levels respectively). Moreover, fish carcass composition was not significantly different among treatments. Instead, significant augmentations in feed conversion ratio (1.36, 1.54 and 1.73 respectively) and reductions in protein retention (35.7%, 33.5% and 29.0% respectively) occurred as protein levels increased. Results indicate that at the lowest protein level, pacú growth rates and carcass composition were similar to the other experimental treatments, with a significant improvement in pond water quality and feed utilization efficiency.     

The diet of hybrid red tilapia Oreochromis niloticus (L.) Oreochromis mossambicus (Peters) reared in the freshwater ponds of north-eastern Brazil

To assess potential competition for food with indigenous species prior to their release into reservoirs in north-eastern Brazil, the diet of hybrid red tilapia, Oreochromis niloticus O. mossambicus, maintained without supplementary feed in monocultures in freshwater ponds, was studied. The stomach contents of 160 fish (140–220 mm total length), collected monthly from February to September 1993, were analysed. Fish of all size categories were found to be phytoplanktivores. A total of 40 microalgal species were observed in the stomach contents (17 species of Chlorophyceae, 11 species of Bacillariophyceae, eight species of Cyanophyceae, three species of Chrysophyceae and one of Euglenophyceae), together with a few rotifers and some organic material. In terms of cell numbers, the overall composition of the diet was 70% Chlorophyceae, 21% Bacillariophyceae, 3% Chrysophyceae, 2% Cyanophyceae, 1% Euglenophyceae and 3% organic matter. Neither diet composition nor stomach fullness varied with fish size. However, fish had relatively fuller stomachs, with higher proportions of Chlorophyceae, Bacillariophyceae and Cyanophyceae, during the rainy season. Hybrid red tilapia appear unlikely to compete for food with a native species and so may have a role in aquaculture or for deliberate release into reservoirs in north-eastern Brazil.     

Reproductive Biology of Puntius sarana, an indigenous species, and Tilapia rendalli (melanopleura), an exotic, in an Ancient Man-Made Lake in Sri Lanka

Investigations on the reproductive biology of Puntius sarana an indigenous species and Tiiapia remialli (melanopleura) an exotic, in an ancient man-made lake, Parakrama Sarnudra (Sea of Parakrama), in Sri Lanka, carried out from February 1978 to May 1979 are presented. The overall female to male ratio in T. rendalli and P. sarana were 1.1:1.0 and 1.5:1.0, respectively. Considerable deviation from the mean ratio was observed and are attributed to their spawning behaviour and migrations. In the larger size groups in T. rendalti males were dominant while the reverse was observed in P. sarana. Both species were found to breed through out the year, with well defined peaks in the case of P. sarana which were coincidental with the main rainy seasons. Both species are multiple spawners, fecundity ranging from 760 to 6160 in T. rendalli with length and weight varying from 18.8 to 25.8 cm and 126 to 380 g, respectively. In P. sarana. with a length of 23.8–38.0cm and a weight of 180–792 g, fecundity ranged between 16,000 and 290,000.     

Culture-based fisheries in small reservoirs in northern Vietnam: effect of stocking density and species combinations

This study was conducted in 20 reservoirs, ranging in size from 4 to 30 ha, in the mountainous, northern region of Vietnam, in ThaiNguyen and YenBai provinces, over two growth cycles in 2002/03 and 2003/04. The reservoirs are leased by farmers for fishery activities from the provincial administration, and the trials were managed by the lessee farmers. Three species combinations in ratios (by fingerling weight) of grass carp: silver carp: bighead carp: common carp: mrigal 1:2:1:1:3 (A), 1:3:1:1:2 (B) and 1:2:1:1:2 (C) were used as seed stock. The overall mean yield of stocked fish in 2002/03 and 2003/04 growth cycles in reservoirs in ThaiNguyen and YenBai provinces was 165 (±21) and 190 (39), and 287 (±22) and 325 (±24) kg ha^?1 respectively. The yield in reservoirs in both provinces, in both growth cycles and irrespective of the species combinations, increased in relation to stocking density. In reservoirs in ThaiNguyen Province, the species combination B gave the lowest yield (both growth cycles and overall), and differed significantly (P<0.05) from combinations A and C. The stocking efficiency (ratio of the yield of stocked fish in kg ha^?1 to the weight of the stocked fish in kg ha^?1) in reservoirs in ThaiNguyen Province ranged from 2.9 to 5.1 over the two growth cycles and that in YenBai from 2.8 to 3.9. There was no discernible trend between growth cycles and/or between species combinations. The major cost incurred was for fingerling procurement. In all instances, a net profit was accrued. The mean (±standard error (SE)) net profit ha^?1 (in 10³VN dong; approximately 15 500 VND=1 US$) was 885 (±270) and 864 (±214), and 1322 (±176) and 1600 (±150) for the growth cycles 2002/03 and 2003/04 for reservoirs in ThaiNguyen and YenBai provinces respectively. Between the two growth cycles, the net profit increased in eight and three reservoirs from YenBai and ThaiNguyen, respectively, the maximum increase being recorded in Khuan Gio (165%) and Dong Man (39%) reservoirs.     

Effects of replacement of animal protein by soybean meal on growth and carcass composition in juvenile Australian freshwater crayfish

A feed trial was conducted for 59 days with juvenile Cherax destructor, mean weight (se) 0.61 (0.01) g, reared communally and maintained on 16 isoenergetic diets containing crude protein levels of 15, 20, 25, and 30%. For each protein level the fish meal component was replaced by soybean meal to produce diets in which 0, 20, 40, or 60% of the protein originated from soybean meal. Mean percentage weight gain per day ranged from 2.98% (15% protein, 60% soybean meal diet), to 11.75% (30% protein, 40% soybean meal diet). When soybean meal was included at a level of 40–60%, growth rate was reduced relative to that achieved with control diets at 15% and 20% protein levels. In no case did a 20% substitution significantly affect growth over that achieved with controls. A two-way interaction occurred between dietary protein and the level of dietary soybean meal. Feeds of higher protein content appeared to permit higher soybean meal inclusion levels without significantly affecting growth. Increases of 5% protein produced a significant improvement in growth when soybean meal contributed from 40–60% of the total protein. This effect was less pronounced in the control diets and the 20% soybean meal series. The percentages of protein increased and lipid decreased in the carcass as the level of dietary protein increased. A similar effect occurred by increasing the soybean meal substitution level to 60%. An obvious trend in carcass moisture, energy, and ash did not occur. A protein requirement of 30% is apparent when fish meal and soybean meal are included in diets at levels of 20% and 24% respectively. A maximum weight of 14.13 g was recorded for an individual fed the 30% protein, 20% soybean meal diet.     

The dietary protein requirements of young tilapia and an evaluation of the least cost dietary protein levels

In this study our goal was to establish the most economical dietary protein content for tilapia culture. To this end we assessed the relationship of growth, measured as percent average daily gain (% ADG), food conversion ratio (FCR) and protein efficiency ratio (PER) of young of four tilapiine species, Oreochromis mossambicus, O. niloticus, O. aureus and Tilapia zillii, for which experimental growth data were available, in relation to body weight and dietary protein content (% protein).

The relationship of % ADG to % protein in young tilapia weighing less than 1 g or 1–5 g was found to be a second order polynomial quadratic function whereas FCR and PER were linearly related to % protein. % ADG, FCR and PER were correlated better to body weight (curvilinearly) than % protein in both size groups, and multiple regressions were derived between the above parameters.

The most economical dietary protein content was evaluated from the polynomial quadratic function utilizing 95% confidence limits and also from the multiple regressions incorporating FCR and % ADG for a set of nearly isocaloric diets (gross energy) of different protein content ranging from 12% to 44%. Data derived from the foregoing approaches showed that young tilapia weighing between 1 and 5 g require 28% of the diet as protein. This dietary protein content, however, is considerably less than the protein level which supports maximum growth, namely 34%.     

Genetic variability in four hatchery strains of coho salmon, Oncorhynchus kisutch (Walbaum), in Chile

Coho salmon, Oncorhynchus kisutch (Walbaum), is intensively cultured in Chile. An increasing proportion of the eggs necessary to sustain the culture are locally produced by some hatcheries. However, there is no information about the origin or the genetic variability in these strains. The present study analysed allozymic variability and its distribution within and between some commercial strains of coho salmon in southern Chile. The genetic variability was estimated using horizontal starch gel electrophoresis. Samples of coho salmon were obtained randomly from four Chilean hatcheries. Twenty‐five enzymatic systems were examined, representing 51 enzymatic loci. Eight loci showed variability in at least one strain, which represented a total polymorphism (P) of 15.7%. Only the PGM‐1* locus was variable in all strains. The remaining loci were fixed in at least one strain. Total heterozygosity (H_T) and within population heterozygosity (H_S) were 0.35% and 0.36% respectively. The index of genetic diversity (G_ST) was 1.5%. The results confirm previous reports of low genetic variability in cultured strains of coho salmon in Chile, below that observed in their native range, which suggests loss of the genetic variability caused by genetic drift or other causes in these strains.     

Breeding performance of Malaysian mahseer, Tor tambroides and T. douronensis broodfish in captivity

Tor tambroides and T. douronensis are highly valued freshwater cyprinids. Owing to their cultural and economic importance, and concerns over their conservation status, a captive artificial propagation programme was established in Sarawak, Malaysia, to produce seedstock for conservation and aquaculture purposes. This paper describes work that followed the initial breakthrough in artificial propagation of captive, pond‐reared broodfish of the two Tor species, primarily on the overall breeding performance of broodfish over a 3‐year period. Breeding performance generally increased through the study period, indicating an overall improvement in husbandry and breeding techniques since commencing breeding trials. Spawning was induced in most months of the year. Seasonal patterns in spawning performance were not clear, but nevertheless the influence of monsoonal climate patterns was evident as higher breeding performance indicators were observed during the northeast monsoon. Some individual broodfish were injected and stripped up to 11 times during the study, and there were as little as 30 days between successful strippings. Considerable variability was observed in each of the breeding performance indicators with successive hypophysation, although in T. tambroides, there were signs of an increase in some of these indicators with successive hypophysation attempts. Multiple injection of Ovaprim, and repeated stripping of eggs, does not appear to reduce breeding performance, at least for T. tambroides.     

Modelling growth in cultures of Oreochromis niloticus (L.) and Cyprinus carpio L. in Pernambuco, Brazil

Different growth models in cultures of Oreochromis niloticus (L.) and Cyprinus carpio L. were compared in Pernambuco, Brazil. The Chapman–Richards growth model was shown to be the most appropriate for Oreochromis niloticus, while Silva's model best expressed growth for Cyprinus carpio.