Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

This review provides a contemporary account of knowledge on aspects of introductions of non-native fish species and includes issues associated with introduction pathways, ecological and economic impacts, risk assessments, management options and impact of climate change. It offers guidance to reconcile the increasing demands of certain stakeholders to diversify their activities using non-native fishes with the long-term sustainability of native aquatic biodiversity. The rate at which non-native freshwater fishes have been introduced worldwide has doubled in the space of 30 years, with the principal motives being aquaculture (39%) and improvement of wild stocks (17%). Economic activity is the principal driver of human-mediated non-native fish introductions, including the globalization of fish culture, whereby the production of the African cichlid tilapia is seven times higher in Asia than in most areas of Africa, and Chile is responsible for c. 30% of the world's farmed salmon, all based on introduced species. Consequently, these economic benefits need balancing against the detrimental environmental, social and economic effects of introduced non-native fishes. There are several major ecological effects associated with non-native fish introductions, including predation, habitat degradation, increased competition for resources, hybridization and disease transmission. Consideration of these aspects in isolation, however, is rarely sufficient to adequately characterize the overall ecological effect of an introduced species. Regarding the management of introduced non-native fish, pre-introduction screening tools, such as the fish invasiveness scoring kit (FISK), can be used to ensure that species are not introduced, which may develop invasive populations. Following the introduction of non-native fish that do develop invasive populations, management responses are typified by either a remediation or a mitigation response, although these are often difficult and expensive to implement, and may have limited effectiveness.

Current knowledge on non-native freshwater fish introductions

Captive breeding programs are increasingly being initiated to prevent the imminent extinction of endangered species and/or populations. But how well can they conserve genetic diversity and fitness, or re-establish self-sustaining populations in the wild? A review of these complex questions and related issues in salmonid fishes reveals several insights and uncertainties. Most programs can maintain genetic diversity within populations over several generations, but available research suggests the loss of fitness in captivity can be rapid, its magnitude probably increasing with the duration in captivity. Over the long-term, there is likely tremendous variation between (i) programs in their capacity to maintain genetic diversity and fitness, and (ii) species or even intraspecific life-history types in both the severity and manner of fitness-costs accrued. Encouragingly, many new theoretical and methodological approaches now exist for current and future programs to potentially reduce these effects. Nevertheless, an unavoidable trade-off exists between conserving genetic diversity and fitness in certain instances, such as when captive-bred individuals are temporarily released into the wild. Owing to several confounding factors, there is also currently little evidence that captive-bred lines of salmonids can or cannot be reintroduced as self-sustaining populations. Most notably, the root causes of salmonid declines have not been mitigated where captive breeding programs exist. Little research has also addressed under what conditions an increase in population abundance due to captive-rearing might offset fitness reductions induced in captivity. Finally, more empirical investigation is needed to evaluate the genetic/fitness benefits and risks associated with (i) maintaining captive broodstocks as either single or multiple populations within one or more facilities, (ii) utilizing cryopreservation or surrogate broodstock technologies, and (iii) adopting other alternatives to captive-rearing such as translocations to new habitats. Management recommendations surrounding these issues are proposed, with the aim of facilitating meta-analyses and more general principles or guidelines for captive-breeding. These include the need for the following: (i) captive monitoring to involve, a priori, greater application of hypothesis testing through the use of well-designed experiments and (ii) improved documentation of procedures adopted by specific programs for reducing the loss of genetic diversity and fitness.

/pdf/how-well-can-captive-breeding-programs-conserve-biodiversity-1aewr6iig6.pdf

How well can captive breeding programs conserve biodiversity? A review of salmonids

Riskperceptionsareimportanttothepolicyprocess,butthereisoftenawell-established pattern of small risks being over assessed. This is also true with the issue of non-native freshwater fish introductions, where a great majority of research focuses on the few negativecases.Theattitudetowards‘non-natives’isacontinuallyevolvingprocessand varies according to current societal values. Here I show that on the global scale, the majority of freshwater fish introductions are not identified as having an ecological impact while having great societal benefits. Case studies from the African lakes are discussed in order to illustrate contrasting outcomes following fish introductions. Looking into the future, the environmental changes that freshwater ecosystems may encounter will have inevitable implications on the distribution of our native freshwater fish species and the need to rely on non-native introductions may become a growing reality. Aquaculture production is regularly increasing and our dependence on it is likely to become greater as it provides an important substitute for the declining production of capture fisheries. With it the number of freshwater fish introductions will increase and a more realistic attitude, albeit controversial, will need to be debated. This would mean protecting some introductions that present beneficial outcomes for biodiversity alongside a more systematic ban of species or families of fish presenting a higher historical ecological risk. The public perception of risk is something which cannotbeignoredbyanygovernmentorrulingbody,butinordertogainpublicsupport in the fight for conservation of freshwater fish biodiversity, the message needs to be clear, detailed and educational.

https://www.fws.gov/southwest/sjrip/pdf/WBM_Gozlan_2008_Introduction_non-native_fish%20is_it_all_bad.pdf

Introduction of non-native freshwater fish: is it all bad

The introduction into Lake Kivu of the planktivorous fish Limnothrissa miodon at the end of the 1950s raised major concern about the fate of mesozooplankton, but few data were available to assess the impact of predation. In this study, we followed zooplankton variations in Lake Kivu for 3.5 years. Present Lake Kivu mesozooplankton is dominated by cyclopoid copepods (Thermocyclops consimilis, Mesocyclops aequatorialis and Tropocyclops confinis), but cladocerans and rotifers are also present. Each year, total crustacean abundance in the plankton increased to a distinct seasonal maximum following a rise of phytoplankton production associated with a deep epilimnetic mixing in the dry season (August-September). This dependence on phytoplankton resource suggests that mesozooplankton dynamics in Lake Kivu is mainly bottom-up controlled, contrary to expectations from the food web structure. However, measurements of body size indicate that sardine predation affects the cladoceran Diaphanosoma excisum, whereas the larger copepods may efficiently escape predation by migration in the deep mixolimnion at daytime. Total biomass of mesozooplankton in Lake Kivu is lower than in lakes Tanganyika and Malawi. This may be related to the disappearance of a large grazer that existed before the sardine introduction, whereas the large lakes of the same region have a more complex pelagic food web, with piscivorous fish, and with calanoid copepods, which can more efficiently exploit phytoplankton production.

/pdf/zooplankton-of-lake-kivu-east-africa-half-a-century-after-gtxt6cj5g9.pdf

Zooplankton of Lake Kivu, East Africa, half a century after the Tanganyika sardine introduction

An aquatic fern, Azolla microphylla (strain 175 MI, Catholic University of Louvain, Belgium), a natural source of protein, was used in this study to produce low-cost feeds for the omnivorous-phytoplanktonophagous tilapia, Oreochromis niloticus L. Fish were grown in a recirculating system and fed with six different diets in triplicate groups. Diets were formulated with approximately similar total protein, ranging from 27.25 to 27.52% dry weight (dw), gross energy content ranging from 85.1 to 96.5 MJ kg(-1) dw, and with different levels of dry meal Azolla (0, 15, 20 30 40, 45% diet dw). All diet levels with incorporated Azolla meal exhibited weight gain, thus it can be assumed that Azolla in good combination with local products can be used to promote fish culture development. The Azolla-free diet and the diet containing 15%Azolla produced the same growth performance. However, the least expensive diet containing 45%Azolla also exhibited growth and can be used as a complementary diet for tilapia raised in fertilized ponds.

Use of a natural aquatic fern, Azolla microphylla, as a main component in food for the omnivorous-phytoplanktonophagous tilapia, Oreochromis niloticus L.

Etude des populations piscicoles de l'Ubangui et tentatives de sélection et d'adaptation de quelques espèces à l'étang de pisciculture

Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand-fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g−1) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by-products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P 0.05). In experiment 2, three stocking densities, 1, 3 and 5 m−2, were assigned to three treatments T1, T2 and T3 respectively. Fish were hand-fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day−1), the specific growth rate (1.90–2.20% day−1) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P 0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are−1 and 28.79 ± 3.66 to 101.42 ± 7.48 kg are−1 year−1, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m−2 produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m−2 with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.

/pdf/effects-of-stocking-density-on-growth-yield-and-4wzotlxz26.pdf

Jean-Claude Micha

Papers

Zooplankton of Lake Kivu, East Africa, half a century after the Tanganyika sardine introduction

Use of a natural aquatic fern, Azolla microphylla, as a main component in food for the omnivorous-phytoplanktonophagous tilapia, Oreochromis niloticus L.

Etude des populations piscicoles de l'Ubangui et tentatives de sélection et d'adaptation de quelques espèces à l'étang de pisciculture

Effects of stocking density on growth, yield and profitability of farming Nile tilapia, Oreochromis niloticus L., fed Azolla diet, in earthen ponds

Modeling trophic interactions in Lake Kivu: What roles do exotics play?