Sexing and reproductive habits of abalone with a special emphasis on Omani abalone

Abalones are dioecious (separate male and female sex) as abalones develop their eggs and sperm in gonads located under the soft skin visible between the foot and the shell.

There is no sexual dimorphism of the shell structure and so the sexing of abalone cannot be done based on the external differentiation and is only determined through the visual inspection of gonads which could be seen if the foot and mantle are forced away from the right side.

Male gonads tend to be from white to creamy beige in color while females’ ovaries are usually darker. The photos in this post belong to Omani abalone, Haliotis mariae in which male gonads (left) are creamy white, while females have greyish-green gonads (right). However, in spent females, the color of gonads may fade.

Like all abalones, Omani abalones are broadcast spawners where both male and female release their gametes directly in the water whereas egg fertilization and embryonic development take place.

Omani abalone (male gonads) Omani abalone (female gonads)

 

 

 

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Historic information- Herring fishery in London during 1935 and before

Source: The heart of England        by: Ivor Brown       year:1935

The description related to the photos reads: East Anglian chronicles are written, so to speak, in herring-bone. Herring were once currency on those shores; rents were paid in them and international affrays followed the Dutchmen’s pursuit of the shoals into English waters. “The fishery”, wrote Nashe of herrings in 1567, “is a great nursery for seamen and brings more ships to Yarmouth than assembled at Troy to fetch back Paris. That town had forty brewers in employ for thirsty fishers. But now the herring-trade, though great, does not suffice its workers. Appeals are made to Parliament and public for remedy; the first must act, the second must eat, that Yarmouth and many similar harbours, closely dependent on the herring, may be saved.

The caption for the two photos reads: “The herring fleet, in action and repose”

London - herring fleet (01) London - herring fleet (02)

 

 

Permanent link to this article: https://fishconsult.org/?p=10408

Recovery plan of the European eel, Anguilla anguilla in the Guadalquivir River basin, Spain

Credit: Glenda Vélez Calabria (Colombia)

The photos show a part of the program carried out in the University of Cordoba, Spain. The university program contributes to the EU-funded program on the recovery plan for the European eel in the Guadalquivir River basin. This project component includes two stages which are namely, field trips and determination of the pigmentation stages of glass eels. The main objective was to review the creels or traps that had been placed previously in the Doñana National and Natural Park and the Guadiamar Green Corridor, in order to keep track of the biological conditions of adult eels that start their migration process towards the sea. It may worth mentioning that the European eel (Anguilla anguilla) was listed as ‘critically endangered’ by the International Union for the Conservation of Nature (IUCN). One of the photos shows the glass eel while the second photo shows the adult European eel.

European eels - adult eel European eels - glass eel

 

 

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Fish trapping in the Northen lakes in Egypt

The two photos show tapping of fish using wire traps. Fish trapping is used in any of the four northen lakes in Egypt which are namely: Manzala, Burullus, Edku and Maryut. Water shallowness, and the spread of aquatic weeds favor the use of fish traps especially the cost of these traps is very low. Most of fishermen can construct these traps themselves. Based on fishery statistics, tilapias are the major species caught in these traps. Usually, fishermen place these traps in locations expected to have rich fishery stocks.

The mesh size of traps determines the size of fish trapped. Therefore, fishery regulations usually determine the permissible mesh size of these traps. The same is true in regard the locations of these traps. It may be of interest to know that fishery regulations in Egypt limited the length of the fishing boats to be longer than 6 meters which cannot reach shallow and vegetative areas which serve as nurseries for  small fish.

Fish trapping in northen lakes (01) Fish trapping in northen lakes (02)

 

Permanent link to this article: https://fishconsult.org/?p=10398

Culture of crawfish, Procambarus clarkia in Louisiana, USA

The main farmed crawfish species are red swamp crawfish (Procambarus clarkii) or white river crawfish (Procambarus acutus). The essential elements in crawfish farming include traps and baits.

The photo which was taken in a crawfish farm in Louisiana, USA during 1980s show a type of traps which was in use during 1980s.

Trapping: Bait trapping is the only harvesting method of crawfish. Even though there are many styles and sizes of traps that are used in the trapping of crawfish, their efficiency is judged by their trapping capacity of the target size of crawfish. Factors involved include trap shape, mesh size and mesh shape (square or diagonal). In general, about 12-g average size is the minimum marketable size of crawfish.

Baits: Bait, depending on its type and quantity used is the single highest expense in crawfish production. Bits are either natural fish or formulated baits. Traditional bait for traps has been some type of oily fish such as gizzard shad, salmon trimmings or carp. Fish are cut into pieces and dropped daily into the trap. Beef melt and chicken parts have been also used.

Formulated crawfish baits, are commercially produced and often made mainly of cereal grains, supplemental with fish oils, commercial flavoring agents and a binder. These baits are easier to handle and store compared to fish bait.

Harvesting: Crawfish growers may come to each trap daily and dump the crawfish into a holding container. Harvested crawfish is taken to holding facility for further processing. It is assumed and based on the mesh size of the traps; nearly all of the crawfish caught in traps are of marketable size. As shown in the photo, growers may use boats which can operate in shallow waters during the harvesting. Usually, harvested traps are baited during the same visit. The time of harvesting takes into consideration the market demand as well as the environmental factors; no harvesting takes place if pond water is iced or if the cold water temperature inhibits crawfish movement.

Crawfish trap (01) Crawfish harvesting (02)

 

 

 

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Enumeration of plankton using Sedgewick-Rafter chamber

This 2-slide information bite addresses the use and specifications of the chamber. The procedures of filling the chamber and so the microscopic examination has been addressed in details.

http://fishconsult.org/wp-content/uploads/2014/02/Enumeration-of-plankton-using-a-Sedgewick-Rafter-chamber.pdf

 

 

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Establishing a Station for the production of commercial and native fish seed in the municipality of Armer, Tolima, Colombia – in Spanish

This project proposal has been developed by a group who participated in Fish Culture Development training course in 2007 under the supervision of Dr. Abdel Rahman El Gamal.

This project addresses the establishment of seed production station for five commercial and native fish species in Tolima, Colombia for the purpose of meeting the demand of fish farms in Tolima. In addition to seed production, the project offers the opportunity to conduct applied research towards developing valid and appropriate technologies as well as conducting training programs for rural communities.

The project document includes technical details and physical requirements supported by images and illustrations whenever needed.  The project budget as well as the economic analysis has been covered.

Cachama blanca (Piaractus brachypomus), Tilapia (Oreochromis sp.), bocachico (Prochilodus magdalenae), moncholo (Hoplias malabaricus) y nicuro (Pimelodus blochii)

The participatory approach between fish farmers and the scientists in the Department of Tolima has been emphasized.

http://fishconsult.org/wp-content/uploads/2014/02/Estación-de-Alevinaje-en-la-Granja-del-Municipio-de-Armero-Tolima-Colombia.pdf

Permanent link to this article: https://fishconsult.org/?p=10379

Sampling of subsurface water in fish ponds

This 2-slide bite explains the sampling of subsurface water in a fish pond.The water sampler has been covered and illustrated and so the procedures in obtaining water samples at a specified water depth in an earthen pond.

[gview file=”http://fishconsult.org/wp-content/uploads/2014/02/Sampling-of-subsurface-water-in-fish-ponds.pdf”]

 

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Historic information – conservation measures of snails in Ahafo, Ghana

Source of the text: Pageant of Ghana    By: Freda Wolfson      Year: 1958

Snails are valuable protein source among the forest people. In the district of Ahafo (Ghana), lies one of the richest areas for snail catching in Ghana. During the snail hunting season, whole villages –men, women and children –migrate into the forest, leaving only the old to look after their homes. Everyone goes out each morning, returning late in the evening with their baskets with their catch of live snails. Women carry out the processing of collected snails including smashing, drying and smoking.

The old men and chiefs in Ahafo are in charge of the conservation of snail stocks. These measures are represented in fixing the hunting season and giving permissions for strangers to collect snails on payment. The conservation includes taking the tough decisions whenever required. For example, the old men and chiefs in Ahafo decided to ban the snail-catching in 1924 for three years based on their fear of the possibility of the complete destruction of the snail stocks.

Ghana (conservation of snail population)

 

 

Permanent link to this article: https://fishconsult.org/?p=10372

Global fish trade in the early 1900s

The information in this 2-slide bite has been distilled from the document of the United Nations conference which was held in Hot Springs, Virginia, USA during the period May 18 – June 3, 1943. Fish trade has been focused upon in the bite especially in related to salted fish. The prices of salted fish in relation to World War II has been addressed in the bite including actions taken by producing countries (e.g. subsidies). The outlook of fresh and frozen fish trade in relation to the development of cooling and freezing systems during storage and transport has been also addressed.

http://fishconsult.org/wp-content/uploads/2014/02/Global-fish-trade-during-the-early-1900s.pdf

Permanent link to this article: https://fishconsult.org/?p=10364

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