8123

• UCREFRP Catalog Number: 8123
• Author: Wydoski, R. S.
• Title: Coordinated Hatchery Facility Plan
• USFW Year: 1994.
• USFW - Doc Type: Need for Captive-Reared Endangered Fish and Propagation Facilities.
• Copyright Material: NO

Oxygen. Fishes differ in their requirement for dissolved oxygen. The
oxygen content of water is affected chiefly by water temperature and
the partial pressure of the gas. However, respiration of the fish and ,
biological oxygen demand of metabolic wastes are also important. As
the temperature increases from 50 F (10 C) to 77 F (25 C), the
metabolic rate of the endangered Colorado River fishes increases
proportionally. The loading rate of fish and the feeding rate are
critical in oxygen consumption by fish and the biological oxygen
demand of metabolic wastes that are influenced by water temperature
and pH. The proposed minimum dissolved oxygen in parts per million (=
milligrams per liter) is 4.0 for inflow water to rear the endangered
Colorado River fishes. The water flow required with different inflow
dissolved oxygen levels per pound of food fed to fish daily is '
summarized in Table 8.
Nitrogen. Dissolved nitrogen is not a problem to fish if the level is
at 100% saturation or below. However, when the level rises above
100%, the fish may be affected by gas bubble disease. Even at levels
as low as 102%, gas bubble disease may be a problem. When water is
supersaturated with nitrogen gas, fish blood tends to become '
supersaturated with nitrogen as well. When the gas pressure is
decreased or the water temperature is increased, nitrogen is released
from the bloodstream in the form of bubbles. The bubbles (emboli)
lodge in blood vessels forming restrictions to circulation that result
in gas bubble disease (similar to the bends in human divers). The
bubbles occur in the gills, fin rays, under the skin, and pressure, in
severe cases, may cause the eyes to bulge from their sockets (Rucker
1972). Gas bubble disease in fish generally results in death by
asphyxiation. Water drawn from deep wells, water heated from snow
melt, water that has plunged over waterfalls, and water that is
aerated by a water pump can be supersaturated with nitrogen gas.
Various methods are available to remove excess nitrogen by passing
water through sealed columns, oxygen injection, etc. that are
summarized in a series of papers (Owsley 1981; Visscher and Dwyer
1990; Westers et al. 1991).
Ammonia. One of the chief by-products of fish metabolism is ammonia.
Some of the ammonia dissolves in water to form ammonium ions and the
remzAv der \ s presea?. as va?oo?Zed a oa?a. ?o?oa?teb a ??a t5 ?o???.
to fish and increases with higher pH values and warmer water
temperature (see Table 9 for the relation between these variables).
Unionized ammonia levels become toxic to fish when they exceed 0.0125
parts per million (milligrams per liter). Therefore, as the water pH
and temperature increase, more water flow is required per pound of ,
food that is fed to fishes to avoid toxicity problems (Table 9).
Flow. A minimum flow of 6 gallons per minute is required per pound of '
food that is fed daily to reduce the concentration of unionized
ammonia. This flow recommendation is based on the assumption that the
pH is between 7.5 and 8.0. Less flow is required for pH values that
are 7.5 or less. More flow is required for pH values that are above
8.0. The flow required at various dissolved oxygen levels per pound
of food used in indoor facilities is summarized in Tables 8 and 9.
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