Fish Ecology, Fisheries, and Aquaculture

CHAPTER 23 Fish Ecology, Fisheries, and Aquaculture

Introduction

• Much of the economic impetus for protecting freshwaters arises from the maintenance of productive sport and commercial fisheries.

• Fishes dominate many freshwater food webs as the top predator in streams and lakes.

• Fishes are good indicators of water quality and serve as model organisms for physiological and behavioral research.

• Understanding fish ecology and traits is crucial for effective fish conservation (Angermeier, 1995).

• This chapter examines fish community biogeography, factors affecting fish growth, survival, reproduction, population dynamics, fisheries management, and aquaculture methods in light of freshwater ecology principles.

Biogeographical and Environmental Determinants of Fish Assemblage Diversity

• Fisheries biologists are increasingly focused on managing species beyond those traditionally harvested for recreation or food.

• Conservation efforts have expanded to include non-game species, biodiversity restoration, and protection of endangered species.

• Fishery yield typically increases with species diversity within communities (Brooks et al., 2016).

• Factors influencing fish diversity and distribution are explored from general patterns to specific cases.

Patterns of Fish Diversity

• Current estimates indicate comparable species numbers in freshwater and marine systems, though all species are not yet described.

• Notably, the Amazon Basin features more known fish species than the Atlantic Ocean despite marine fish having a longer evolutionary history.

• Geographical isolation in continental waters increases reproductive isolation and speciation potential:

  • Speciation largely occurs within drainage basins.

  • Larger drainage basins exhibit greater species diversity (Oberdorff and Hugueny, 1995; Guégan et al., 1998).

  • Islands generally have lower fish diversity due to small watersheds, consistent with island biogeography theory from Chapter 11.

• Fish species richness is higher in tropical regions compared to temperate zones:

  • Data by Matthews (1998) indicates that approximately 7% of sampling attempts in both tropical and temperate streams yielded no fish, signifying areas unsuitable for fish.

  • Tropical streams can have a maximum biodiversity significantly higher than temperate streams, with upwards of 50 species in many tropical samples.

  • Various factors contributing to higher diversity in tropics include:

  • Glaciation led to extirpation of fish species in higher latitudes.

  • Longer evolutionary timescales allow for more generations of fish per year in the tropics.

  • Greater terrestrial net productivity linked to fish diversity in tropical regions (Oberdorff and Hugueny, 1995; Guégan et al., 1998).

• In North America, there are about 740 fish species, with approximately 300 species in the Mississippi basin, where extensive evolutionary history and higher productivity likely led to higher fish diversity. Lack of glaciation contributes to this diversity.

Effects of Habitat on Fish Diversity

• Fish diversity generally increases with distance from headwater streams:

  • Smaller streams are more vulnerable to drying, debris torrents, and catastrophic flooding.

  • Floodplains of larger rivers feature diverse habitats (e.g., wetlands, oxbows).

• Habitat structure significantly influences where fish congregate:

  • Key habitats include cut banks, woody debris, and deep pools.

  • Dams can disrupt fish populations by obstructing migratory routes.

• Pollution affects fish diversity; heavily polluted waters often support low or no fish populations.

Importance of Amazonian Fish Assemblages

• The Amazon River's annual flooding allows fish access to riparian forests and temporary connection to small ponds, promoting biodiversity.

• The total number of fish species in the Amazon is estimated to be between 2,500 and 3,000.

  • Some species migrate from the main river into tributaries to spawn, facilitating local fishery practices.

  • Ichthyochory (seed dispersal by fish), particularly prevalent in South America, illustrates mutualistic relationships between fishes and riparian plants, enhancing biodiversity and connecting aquatic and terrestrial ecosystems.

Physiological Aspects Influencing Growth, Survival, and Reproduction

• Energetics underpin the growth, survival, and reproduction of fishes. Environmental extremes drain energy, affecting fish success.

• Energy requirements vary based on external conditions:

  • Survival requires energy, growth demands additional energy, and reproduction is the most energy-intensive process.

Osmoregulation in Freshwater Fishes

• Osmoregulation is vital for freshwater fishes since they are hypertonic relative to their environment, necessitating the regulation of internal ion concentrations.

• Kidneys are crucial for excreting excess water, with certain species (diadromous) adapting to varying salinities in different environments.

• Fishes in dilute waters may have specialized transport mechanisms for ion retention.

Temperature and Its Effects on Fish Physiology

• Temperature impacts fish metabolism:

  • At low temperatures, metabolic rates decline, with increased viscosity of water requiring more energy for swimming (22% decrease in viscosity and doubled metabolic rate from 13°C to 23°C).

  • High temperatures can lead to stress or death in fishes, along with limits to thermal adaptation.

• Physiological responses and adaptations influence thermal tolerance among various fish species:

  • Studies by Comte and Olden (2017) indicate that higher thermal tolerances may lead to reduced physiological plasticity, limiting adaptation potential.

• Optimal temperature ranges vary among species, influencing growth, survival, and reproduction:

  • Temperature requirements for spawning can be more stringent than growth requirements.

Dissolved Oxygen Requirements

• Dissolved oxygen levels are critical for fish respiratory functions; oxygen demand increases with temperature.

• Fish can exhibit stress responses to low oxygen, increasing ventilation rates, which consumes additional energy.

Nutrition and Dietary Needs

• Dietary composition impacts fish growth, survival, and reproduction:

  • Fish diets consist of proteins, carbohydrates, lipids, vitamins, and minerals.

  • High-quality food can mitigate lower energy content from poor-quality options, and dietary adaptations vary by feeding strategy (e.g., piscivores vs. herbivores).

Population Dynamics of Fishes

• Key characteristics of fish population dynamics encompass population size, growth rates, recruitment, mortality, and reproductive output (fecundity).

• Understanding size and age class distributions is essential for managing fish populations:

  • Most fishes exhibit indeterminate growth and can increase in size as they age if energy needs are met.

  • Length is typically easier to measure than mass, as mass is logarithmically related to length.

Age and Size Class Analysis

• Indices like Relative Stock Density (RSD) assist in assessing population structures:

  • RSD is the percentage of fish within a specific length relative to the total population size, giving insights on overall fish health and fishery quality.

Age Determination Techniques

• Length frequency analysis and hard structures (e.g., scales, otoliths) are common methods for aging fish populations:

  • Growth marks on otoliths indicate yearly growth patterns.

Life Tables for Population Management

• Life tables aid in understanding recruitment and mortality rates among size classes, impacting fish population management strategies.

Regulating Exploitation of Fish Stocks

• Effective management practices are necessary to ensure sustainable fish stocks and mitigate the risk of overexploitation, commonly described by the tragedy of the commons.

• Maximum Sustainable Yield (MSY) is calculated based on the number of adult fish against their reproductive potential, though its usage has waned due to inherent limitations.

Management Techniques for Sustainable Fisheries

• Management may involve regulations concerning the number and size of fish harvested:

  • Seasonal limits, creel limits, and size limits are common regulatory measures.

  • Strategies may extend to slot limits to improve the growth rates of fish populations.

  • Protecting spawning periods can mitigate the vulnerability of fish during critical life stages.

Stocking for Fisheries

• Stocking strategies aim to maintain sustainable fisheries:

  • Introductions of new or native species can support management initiatives and help recover certain populations.

  • The rate of fish introductions has drastically increased, especially for aquaculture and natural stock improvement (Gozlan et al., 2010).

Potential Risks of Stocking Programs

• Potential issues from stocking include:

  • Competition, predation, and hybridization with native populations.

  • Genetic diversity concerns and disease transmission risks.

  • Whirling disease and other pathogens stemming from human stocking practices illustrate these risks.

Aquaculture

• Aquaculture, which includes the cultivation of fish, crustaceans, and mollusks, serves as a significant food source for many globally.

• Sustainable practices, disease control, and ecological understanding are paramount within aquaculture frameworks.

• Various species and methods have evolved, relying on extensive traditional knowledge and ecological practices, especially in regions like Southeast Asia where polyculture systems have been successful.

Challenges in Aquaculture

• Aquaculture faces difficulties such as disease management and environmental impacts of nutrient loading.

• Innovations focused on algal production for biofuels are emerging within the broader aquaculture context.

Here is a list of key terms and their definitions from the provided notes:

• Ichthyochory: Seed dispersal by fish, illustrating mutualistic relationships between fishes and riparian plants, enhancing biodiversity and connecting aquatic and terrestrial ecosystems.

• Hypertonic: A state where freshwater fishes have a higher internal ion concentration relative to their environment, requiring osmoregulation to maintain balance.

• Diadromous species: Fish species that adapt to varying salinities as they move between freshwater and marine environments.

• Indeterminate growth: A characteristic of most fishes, meaning they can continue to increase in size as they age if sufficient energy is available.

• Relative Stock Density (RSD): An index used to assess fish population structures, calculated as the percentage of fish within a specific length range relative to the total population size.

• Otoliths: Hard structures in fish (ear bones) used in age determination, as they display growth marks indicating yearly patterns.

• Maximum Sustainable Yield (MSY): A concept for fisheries management calculated based on the number of adult fish against their reproductive potential, aiming to ensure sustainable harvest rates.

• Slot limits: A fisheries management strategy involving regulations on a range of fish sizes that can be harvested, often to improve growth rates of fish populations.

• Whirling disease: A pathogen that can be transmitted through stocking practices, illustrating a risk to native fish populations.

• Aquaculture: The cultivation of fish, crustaceans, and mollusks, serving as a significant global food source.