An aquaculture system including, at least one grow-out tank; a fluid treatment system including a fluid treatment device, a recirculation pump and fluid connections to each of said at least one grow-out tanks for circulating fluid from each of the at least one grow-out tanks through the fluid treatment device; and at least one fluid delivering device which is connected to the fluid treatment system for delivering said circulated treated fluid to said at least one grow-out tank, which fluid delivering device includes an outlet which can be provided in a position within the at least one grow-out tank such that the treated fluid delivered out from the outlet will be delivered along a bottom of said at least one grow-out tank wherein the outlet of the at least one fluid delivering device is configured such that it can be rotated in order for delivering the fluid in different directions along the bottom of the grow-out tank, wherein the at least one fluid delivering device is configured for delivering the treated fluid to substantially the whole bottom of said at least one tank at a velocity which is enough for resuspending sedimented particles, wherein said fluid treatment system is connected to and is serving said at least one grow-out tank intermittently with time constraints which are based on cultivation conditions for an aquaculture in said at least one grow-out tank.

An apparatus for cleaning nets underwater formed from a propeller housing with a centrally disposed axis with a plurality of blades extending therefrom. An outer perimeter ring secured to an outer tip of each blade with a plurality of knuckles secured to the outer perimeter ring. Each knuckle including a curved surface constructed and arranged to be forcefully presented to the aquaculture net upon rotation of said blades for removal of growth by impact and shaking of the aquaculture net. An elastomeric hub prevents spike loads.

An apparatus for cleaning nets underwater formed from a propeller housing with a centrally disposed axis with a plurality of blades extending therefrom. An outer perimeter ring secured to an outer tip of each blade with a plurality of knuckles secured to the outer perimeter ring. Each knuckle including a curved surface constructed and arranged to be forcefully presented to the aquaculture net upon rotation of said blades for removal of growth by impact and shaking of the aquaculture net. An elastomeric hub prevents spike loads.

A tank for water has a bottom and a surrounding wall with an inside and an outside. In a lower portion, the wall is provided with a hatch casing positioned in a hatch opening extending through the wall for access by personnel from the outside to the inside of the tank. The hatch casing is provided with a hatch with an inside and an outside. The hatch in a closed position closes the hatch opening in a liquid-tight manner. The inside of the hatch is flush with the inside of the wall when the hatch is in the closed position. A method for giving personnel access to the tank through the hatch opening is also described.

An abundance of specific species of phytoplankton in a phytoplankton group in which a plurality of kinds coexists is calculated in a simple manner. Based on a reference sample intensity ratio r.sub.0, a reference sample total fluorescence intensity I.sub.0, and an existing quantity K.sub.0 of specific species of phytoplankton, an intensity ratio r.sub.d of other species of plankton is calculated. An analysis sample that is expected to have similarity with the reference sample is irradiated with the excitation light, an intensity of fluorescence emitted from the analysis sample is measured in each of wavelength bands A and B, and an intensity ratio r is calculated. A total fluorescence intensity I is measured, and an existing quantity K of the specific species of the phytoplankton is calculated based on the intensity ratio r.sub.d of other species of plankton, the intensity ratio r, and the total fluorescence intensity I.

A water tank cleaning tool comprising an underwater air vacuum with separate air and water exhaust channels, allowing the user to vacuum and clean the tank substrate without removing water from the tank.

A water tank cleaning tool comprising an underwater air vacuum with separate air and water exhaust channels, allowing the user to vacuum and clean the tank substrate without removing water from the tank.

A tool for cleaning a structure is provided. The tool includes an extension pole having a length, the extension pole including three or more cylindrical segments having different respective diameters, the segments being arranged in a telescoping configuration to permit the length of the extension pole to be adjusted to a desired length; locking nuts structured to releasably lock adjacent ones of the segments to one another; a grip provided on a most proximal one of the segments; and an attachment member provided on a most distal one of the segments, the attachment member being structured to removably attach at least one cleaning accessory.

The present disclosure provides a method for artificial rearing of porcupine pufferfish fries in indoor cement ponds. The method includes the following steps: nursery pond preparation, ponding of newly hatched prelarvae, feeding strategies at fry rearing stages, water quality management during fry rearing, separate ponding of fries, and emergence of fries. Compared with the prior art, the method realizes large-scale production of artificial rearing of porcupine pufferfish fries through a strict control of the water quality and environmental conditions of a nursery pond, along with scientific and reasonable feeding and operation management based on biological characteristics and nutrient requirements of the porcupine pufferfish at different fry breeding stages.

The present disclosure provides a method for artificial rearing of porcupine pufferfish fries in indoor cement ponds. The method includes the following steps: nursery pond preparation, ponding of newly hatched prelarvae, feeding strategies at fry rearing stages, water quality management during fry rearing, separate ponding of fries, and emergence of fries. Compared with the prior art, the method realizes large-scale production of artificial rearing of porcupine pufferfish fries through a strict control of the water quality and environmental conditions of a nursery pond, along with scientific and reasonable feeding and operation management based on biological characteristics and nutrient requirements of the porcupine pufferfish at different fry breeding stages.