Abstract
Mud eel (Monopterus cuchia) is threatened as well as commercially important fish species of
Bangladesh. It has growing demand in the export market and capture from wild is the only source for
export since artificial propagation, fry production and culture techniques have not yet been developed
for mud eel. Knowledge on reproductive biological parameters of any species is a prerequisite for
developing its artificial propagation, fry production and culture techniques. Therefore, this research
was conducted with the following objectives: (i) to explore indigenous traditional knowledge (ITK)
connected with biology and reproduction of mud eel; (u) to identify the peak breeding season of mud
eel through gonadosomatic index (GSI) and gonad histology; (iii) to establish reference haematological
values for mud eel in relation to sex and seasonality; (iv) to develop captive breeding and larval rearing
protocols; and (v) to examine early gonadal development, sex differentiation, intersexuality and sex
change in mud eel. The study was conducted at the Faculty of Fisheries, Bangladesh Agricultural
University, Mymensingh, Bangladesh. For ITK documentation, semi-directive interviews and
questionnaire survey were conducted with experienced mud eel harvesters followed by Participatory
Rural Appraisal (PRA), workshops and personal observation in three sub-districts under Mymensingh
district. ITK data on feeding, nesting, breeding, ecology, etc. of mud eel were useful for this research
towards designing induced breeding programs in captivity. Information on different reproductive biology parameters were obtained through laboratory investigations. Studies of length-weight relationships obtained the mean values of b' to be less than 3.0 (2.27 for male and 2.29 for female)
indicating negative allometric growth of mud eel in the Mymensingh region. The GSI values of both
sexes were found to increase from December to May; the highest in May (6.69±0.31) and the lowest in
November (0.90±0.37). The highest absolute fecundity of 1234 and the lowest of 182 were obtained.
Gonad histology was carried out by applying routine histology prpotocols, followed by haematoxylene
eosin staining. Histo-snaps of gonads indicated the months of April-May-June to be the spawning
capable phase of mud eel. The calculated GSI for these three months were also high compared to other
months of the year. The months of July-August-September were observed as regressing phase,
October-November-December as regenerating phase and January-February-March as developing
phase of gonads for both the sexes. This study also measured blood parameters of adult mud eel
following standard protocols and established year-round reference values for blood glucose,
hemoglobin concentration, total red blood cell count, total white blood cell count, haematocrit and
erythrocyte indices. Production of mud eel fry in captivity was one of the key objectives of this
research. This study has successfully produced mud eel fry in captivity for the first time in Bangladesh
and elsewhere. Trials undertaken for fry production were different forms of 'environmental
manipulation' in the earthen ponds, polyethylene pits, netted pits, cement cisterns and cement ponds.
Again, different materials like mud, mud with organic matters, pipes, aquatic hydrophytes, etc. were
used to mimic the natural environment for breeding. Through an experiment in earthen pit, 5,530 fries
were collected from six pits comprising an area of 57 m². Other trials for fry production in earthen
ponds/pits also became successful with some limitations. Pit dike composed of mud-organic matter
inside the cement cistern successfully produced a total of 1787 mud eel fry from six 4 m² sized cisterns.
Breeding trials in cement ponds had a limited success. Induced breeding trials using exo-hormone (PG
and HCG) failed. After feeding a combination of egg yolk and zooplankton for the first week, a ration
composed of earthworm smash and zooplankton performed best as 'first feed' for one month of
nursing. This research revealed that stocking density of 50 mud eel fry/m² in plastic drums of 0.25 m²,
feeding with earthworm smash at 30% body weight and providing with small diameter pipes as
shelter with sufficient aeration and water exchange might bring the best success in mud eel fry nursing.
Gonad histology of mud eel fry between the lengths of 4 to 18 cm was conducted to investigate
gonadal development and sex differentiation during the early stages of mud eel. It was observed that
gonads of mud eel fry remained histologically undifferentiated below the length of 9 cm. Gonads were
histologically identifiable from the length of 9 cm and between 9 to 11.9 cm, all the gonads were
identified as testicular gonads. From the size of 12 cm, both testicular and intersex gonads were
evident, indicating that some gonads continued as testes and others might be differentiated to form
ovaries. In adult individuals, there were evidences of intersexuality as identified in very few captive
and wild fishes; six out of 360 adult fishes from captivity and wild were identified as intersex gonads.
Histological evidences of intersexuality of gonads indicate sex change in some adult individuals of
mud eel. The sex change took place between regressing and regenerating phases of gonadal development. First hand information on early gonadal development, sexual differentiation,
intersexuality and sex change in developing and adult mud eel has been revealed through this
research. This research produced mud eel fry in captivity for the first time. First feed and fry nursing techniques were also developed through this research.